1
00:00:01,733 --> 00:00:04,033
>> Earth--a unique planet--

2
00:00:04,335 --> 00:00:06,535
restless and dynamic

3
00:00:09,534 --> 00:00:12,469
Continents shift and clash.

4
00:00:12,537 --> 00:00:16,273
Volcanoes erupt, glaciers grow

5
00:00:16,374 --> 00:00:18,742
and recede.

6
00:00:18,810 --> 00:00:20,243
Titanic forces that are

7
00:00:20,278 --> 00:00:22,445
constantly at work, leaving

8
00:00:22,547 --> 00:00:24,181
a trail of geological mysteries

9
00:00:24,282 --> 00:00:26,917
behind.

10
00:00:26,984 --> 00:00:29,619
This episode explores Yosemite

11
00:00:29,720 --> 00:00:32,355
Valley, a magnificent

12
00:00:32,456 --> 00:00:35,826
3,000-foot-deep canyon.

13
00:00:35,893 --> 00:00:37,460
Traveling through time,

14
00:00:37,528 --> 00:00:39,629
scientists are unlocking deep

15
00:00:39,730 --> 00:00:41,965
Secrets trapped inside these

16
00:00:41,999 --> 00:00:44,634
granite walls.

17
00:00:44,702 --> 00:00:47,637
These rocks have literally been

18
00:00:47,705 --> 00:00:50,607
to hell and back, frozen,

19
00:00:50,641 --> 00:00:52,876
drenched, and battered by

20
00:00:52,910 --> 00:00:54,911
earth-shattering forces.

21
00:00:54,979 --> 00:00:56,880
One more chapter in the

22
00:00:56,914 --> 00:00:57,815
incredible story of...

23
00:00:57,816 --> 00:01:02,416
<font color=#FFFF00>Yosemite</font>
Original Air Date on December 22, 2009

24
00:01:02,453 --> 00:01:05,355
-- Sync, corrected by <font color=#00FF00>elderman</font> --
-- for addic7ed.com ---

25
00:01:06,524 --> 00:01:07,991
In the foothills of the mighty

26
00:01:08,059 --> 00:01:09,960
Sierra Nevada, California, lies

27
00:01:09,994 --> 00:01:11,695
a valley like no other on

28
00:01:11,729 --> 00:01:15,799
earth--Yosemite, a 7-mile-long,

29
00:01:15,900 --> 00:01:18,802
one-mile-wide granite canyon.

30
00:01:18,903 --> 00:01:20,537
Here lie some of the most

31
00:01:20,605 --> 00:01:22,539
awe-inspiring geological

32
00:01:22,607 --> 00:01:24,507
features on the planet:

33
00:01:24,542 --> 00:01:26,243
Half Dome--America's most

34
00:01:26,344 --> 00:01:29,446
iconic peak; Yosemite Falls--

35
00:01:29,513 --> 00:01:31,314
the highest unbroken waterfall

36
00:01:31,349 --> 00:01:33,516
on the continent;

37
00:01:33,584 --> 00:01:35,518
And El Capitan--one of the

38
00:01:35,586 --> 00:01:37,153
biggest sheer cliffs in the

39
00:01:37,221 --> 00:01:39,789
world.

40
00:01:39,857 --> 00:01:41,524
The europeans discovered this

41
00:01:41,626 --> 00:01:43,627
astonishing valley only 150

42
00:01:43,694 --> 00:01:45,695
years ago.

43
00:01:45,763 --> 00:01:47,797
>> These sheer walls and granite

44
00:01:47,865 --> 00:01:49,299
cliffs and high waterfalls were

45
00:01:49,333 --> 00:01:52,168
a marvel to them as it is to us.

46
00:01:52,236 --> 00:01:54,070
>> Ever since it shot to fame,

47
00:01:54,171 --> 00:01:55,872
Yosemite has been shrouded in

48
00:01:55,940 --> 00:01:57,874
mystery.

49
00:01:57,875 --> 00:01:59,709
>> It's almost as if there was

50
00:01:59,777 --> 00:02:01,144
a higher power at work that

51
00:02:01,245 --> 00:02:02,312
basically said, "that looks

52
00:02:02,346 --> 00:02:04,247
really good right about there,

53
00:02:04,248 --> 00:02:05,248
and let's just put a little bit

54
00:02:05,316 --> 00:02:06,716
of grass right there, and some

55
00:02:06,784 --> 00:02:08,118
oak, like, an oak woodland right

56
00:02:08,152 --> 00:02:09,886
through there, and that's it!

57
00:02:09,987 --> 00:02:11,254
That's perfect!" because it

58
00:02:11,322 --> 00:02:12,255
doesn't seem like anything was

59
00:02:12,323 --> 00:02:14,157
haphazard. It seems like this

60
00:02:14,258 --> 00:02:16,126
was designed to overwhelm and

61
00:02:16,160 --> 00:02:18,795
then leave people awestruck.

62
00:02:18,863 --> 00:02:20,864
>> Yosemite's unique design has

63
00:02:20,932 --> 00:02:22,699
intrigued scientists for

64
00:02:22,767 --> 00:02:24,701
centuries.

65
00:02:24,769 --> 00:02:25,502
>> I think when you see

66
00:02:25,603 --> 00:02:26,403
something that is this

67
00:02:26,437 --> 00:02:27,337
dramatic, you just have

68
00:02:27,405 --> 00:02:28,505
questions, and the question is,

69
00:02:28,572 --> 00:02:30,040
how did this happen? How do you

70
00:02:30,074 --> 00:02:31,408
get monoliths, these huge

71
00:02:31,475 --> 00:02:33,677
stone structures that are just

72
00:02:33,778 --> 00:02:35,412
rising thousands of feet off the

73
00:02:35,513 --> 00:02:36,746
valley floor? How does that come

74
00:02:36,781 --> 00:02:38,248
to pass? And for over a hundred

75
00:02:38,316 --> 00:02:39,516
years, people have been trying

76
00:02:39,583 --> 00:02:43,420
to answer that question.

77
00:02:43,521 --> 00:02:45,588
>> The story begins in 1870,

78
00:02:45,690 --> 00:02:47,691
when amateur geologist John Muir

79
00:02:47,792 --> 00:02:49,859
went hunting for the answer.

80
00:02:49,927 --> 00:02:52,228
Founder of the Sierra Club, he

81
00:02:52,330 --> 00:02:53,863
funded his obsession with the

82
00:02:53,965 --> 00:02:55,699
valley by herding sheep and

83
00:02:55,766 --> 00:02:58,501
writing articles about Yosemite.

84
00:02:58,569 --> 00:03:00,770
He wrote that "no temple made

85
00:03:00,871 --> 00:03:03,239
with hands can compare with

86
00:03:03,307 --> 00:03:07,777
Yosemite."

87
00:03:07,845 --> 00:03:10,146
Muir scoured the landscape for

88
00:03:10,247 --> 00:03:12,215
clues as to how this unusual,

89
00:03:12,249 --> 00:03:15,218
box-shaped canyon formed

90
00:03:15,319 --> 00:03:17,387
and came up with a radical,

91
00:03:17,421 --> 00:03:20,223
seemingly far-fetched theory.

92
00:03:20,291 --> 00:03:21,324
He believed that the world's

93
00:03:21,392 --> 00:03:23,026
climate was once extremely

94
00:03:23,060 --> 00:03:24,861
different, and the lush canyon

95
00:03:24,929 --> 00:03:26,429
where the Merced River flows was

96
00:03:26,497 --> 00:03:28,665
filled by a gigantic glacier

97
00:03:28,699 --> 00:03:31,034
thousands of feet thick.

98
00:03:31,102 --> 00:03:32,936
Muir proposed that as this river

99
00:03:32,970 --> 00:03:34,871
of ice slowly flowed downhill,

100
00:03:34,972 --> 00:03:36,673
over thousands of years, it

101
00:03:36,774 --> 00:03:38,842
gouged a deep canyon and sliced

102
00:03:38,876 --> 00:03:40,610
vertical cliffs into the granite

103
00:03:40,678 --> 00:03:43,580
walls. But that controversial

104
00:03:43,681 --> 00:03:45,148
idea brought him into conflict

105
00:03:45,216 --> 00:03:46,783
with a fearsome opponent--

106
00:03:46,851 --> 00:03:48,485
the admired California state

107
00:03:48,586 --> 00:03:50,587
geologist, professor Josiah

108
00:03:50,654 --> 00:03:53,223
Whitney.

109
00:03:53,290 --> 00:03:54,591
>> Josiah Whitney did not have

110
00:03:54,692 --> 00:03:56,593
much respect for John Muir

111
00:03:56,694 --> 00:03:58,395
because Josiah Whitney was the

112
00:03:58,496 --> 00:03:59,863
State geologist, and at that

113
00:03:59,930 --> 00:04:02,832
time, John Muir was herding

114
00:04:02,867 --> 00:04:05,201
sheep. Certainly he's thinking,

115
00:04:05,236 --> 00:04:07,470
what does this man know about

116
00:04:07,505 --> 00:04:10,106
this range? How dare he?

117
00:04:10,141 --> 00:04:11,574
>> Whitney believed that this

118
00:04:11,675 --> 00:04:13,676
unusually square, steep-sided

119
00:04:13,744 --> 00:04:14,944
valley could only have been

120
00:04:15,012 --> 00:04:17,213
formed by a sudden, cataclysmic

121
00:04:17,314 --> 00:04:20,116
event. He was adamant that giant

122
00:04:20,217 --> 00:04:21,751
cracks in the earth caused the

123
00:04:21,786 --> 00:04:23,386
valley to pull apart and

124
00:04:23,487 --> 00:04:26,456
dranatically sink...

125
00:04:26,490 --> 00:04:29,092
cleaving steep cliffs as it

126
00:04:29,126 --> 00:04:31,394
fell.

127
00:04:31,495 --> 00:04:33,296
This bitter Whitney-Muir

128
00:04:33,397 --> 00:04:35,465
conflict raged on for decades,

129
00:04:35,499 --> 00:04:37,734
but now scientists are hoping to

130
00:04:37,768 --> 00:04:39,469
figure out this complex puzzle

131
00:04:39,503 --> 00:04:42,472
once and for all. The first

132
00:04:42,506 --> 00:04:43,940
stage of the investigation is to

133
00:04:44,008 --> 00:04:45,508
understand how the rocks

134
00:04:45,576 --> 00:04:47,844
themselves were created. The

135
00:04:47,912 --> 00:04:50,213
canyon is made almost entirely

136
00:04:50,314 --> 00:04:52,315
of Yosemite granite, one of the

137
00:04:52,383 --> 00:04:54,951
hardest rocks in the world.

138
00:04:55,019 --> 00:04:56,853
To understand how this formed,

139
00:04:56,954 --> 00:04:59,122
scientists must travel back in

140
00:04:59,223 --> 00:05:03,593
time to the beginning.

141
00:05:03,661 --> 00:05:07,130
It's 250 million years ago, and

142
00:05:07,198 --> 00:05:10,033
the landscape is very different.

143
00:05:10,101 --> 00:05:12,402
Dinosaurs roam the land and

144
00:05:12,470 --> 00:05:15,305
dominate the skies.

145
00:05:15,372 --> 00:05:17,207
[dinosaurs screeching]

146
00:05:17,308 --> 00:05:19,676
An incredibly rare remnant of

147
00:05:19,743 --> 00:05:21,277
that time has been discovered

148
00:05:21,312 --> 00:05:23,012
Northwest of the valley at

149
00:05:23,047 --> 00:05:25,482
Mount Hoffman.

150
00:05:25,549 --> 00:05:27,283
This patch of softer, reddish

151
00:05:27,318 --> 00:05:30,286
rock is the oldest in the park.

152
00:05:30,321 --> 00:05:32,722
It's sandstone, and it once

153
00:05:32,756 --> 00:05:35,458
covered the entire region.

154
00:05:35,459 --> 00:05:37,760
>> This rock is very different

155
00:05:37,828 --> 00:05:38,561
than most of the rock in

156
00:05:38,629 --> 00:05:39,963
Yosemite. It's much darker in

157
00:05:40,030 --> 00:05:41,931
color, got a different texture.

158
00:05:41,932 --> 00:05:42,832
This was originally a

159
00:05:42,933 --> 00:05:43,933
sedimentary rock that was

160
00:05:44,001 --> 00:05:46,469
deposited in layers.

161
00:05:46,570 --> 00:05:48,471
>> On an ancient shore, sand and

162
00:05:48,539 --> 00:05:51,040
sludge compacted together and,

163
00:05:51,108 --> 00:05:52,475
over millions of years, formed

164
00:05:52,576 --> 00:05:55,645
this sandstone. This tranquil

165
00:05:55,679 --> 00:05:57,714
landscape was transformed by an

166
00:05:57,748 --> 00:05:59,482
earth-shattering event deep

167
00:05:59,583 --> 00:06:01,184
below the surface, and the

168
00:06:01,218 --> 00:06:04,654
evidence lies here in the rock.

169
00:06:04,722 --> 00:06:05,922
>> Here we have this older,

170
00:06:06,023 --> 00:06:07,924
layered sedimentary rock, and

171
00:06:07,992 --> 00:06:09,926
you see that many layers and

172
00:06:10,027 --> 00:06:12,128
banding, which continues across

173
00:06:12,196 --> 00:06:14,731
over in here. But, strangely,

174
00:06:14,765 --> 00:06:16,399
yhis section of granite has cut

175
00:06:16,467 --> 00:06:17,300
tight through the sedimentary

176
00:06:17,401 --> 00:06:19,002
rock and split this section

177
00:06:19,036 --> 00:06:22,605
in two.

178
00:06:22,673 --> 00:06:24,674
>> How this unusual rock

179
00:06:24,742 --> 00:06:26,743
formation formed can be

180
00:06:26,844 --> 00:06:28,578
explained by a simple experiment

181
00:06:28,646 --> 00:06:30,713
using sand and wax.

182
00:06:30,748 --> 00:06:32,815
>> This red wax here represents

183
00:06:32,850 --> 00:06:34,717
the granite, the sand represents

184
00:06:34,752 --> 00:06:37,287
sedimentary rock, and right now

185
00:06:37,354 --> 00:06:38,288
I'm heating it to see what's

186
00:06:38,389 --> 00:06:39,255
going to happen when the wax

187
00:06:39,290 --> 00:06:42,192
melts. Actually I start to hear

188
00:06:42,259 --> 00:06:43,493
some--oh, here it goes. We're

189
00:06:43,527 --> 00:06:45,328
actually getting a little bit of

190
00:06:45,362 --> 00:06:47,497
the wax pushing up through the

191
00:06:47,531 --> 00:06:49,899
sand. And the molten wax is

192
00:06:49,967 --> 00:06:52,068
lighter, and so it's pushing its

193
00:06:52,136 --> 00:06:53,803
way up through the sand, which

194
00:06:53,871 --> 00:06:55,438
represents the sedimentary rock.

195
00:06:55,539 --> 00:06:57,907
Yep, here's some more.

196
00:06:57,975 --> 00:06:59,809
>> It proves the only way

197
00:06:59,877 --> 00:07:01,177
granite could have cut through

198
00:07:01,245 --> 00:07:02,946
this sandstone is if it was

199
00:07:02,980 --> 00:07:04,881
originally molten and able to

200
00:07:04,982 --> 00:07:07,584
flow like a liquid.

201
00:07:07,618 --> 00:07:09,586
>> molten rock forms deep within

202
00:07:09,687 --> 00:07:11,221
the earth, rises up through the

203
00:07:11,255 --> 00:07:13,323
crust, in this case, forced its

204
00:07:13,390 --> 00:07:15,658
way through a crack, expanding

205
00:07:15,759 --> 00:07:18,127
it open, and then cooling and

206
00:07:18,195 --> 00:07:19,729
solidifying to form this band

207
00:07:19,763 --> 00:07:21,197
of granite.

208
00:07:21,232 --> 00:07:22,365
>> This band of granite tells

209
00:07:22,399 --> 00:07:23,766
scientists that Yosemite's

210
00:07:23,834 --> 00:07:25,835
cliffs were once molten and

211
00:07:25,869 --> 00:07:27,737
heated to 1,800 degrees

212
00:07:27,771 --> 00:07:29,639
fahrenheit.

213
00:07:29,673 --> 00:07:31,040
>> 95% percent of the rock in

214
00:07:31,108 --> 00:07:33,042
Yosemite is granite, and I can

215
00:07:33,110 --> 00:07:34,544
see with the naked eye all the

216
00:07:34,578 --> 00:07:36,279
crystals in here. They're fairly

217
00:07:36,313 --> 00:07:37,647
large, and that tells me that

218
00:07:37,681 --> 00:07:39,382
this rock cooled very slowly.

219
00:07:39,450 --> 00:07:40,917
>> Scientists were now on the

220
00:07:40,951 --> 00:07:42,485
hunt for what was generating all

221
00:07:42,586 --> 00:07:45,588
this molten rock.

222
00:07:45,656 --> 00:07:47,957
The investigation led them to

223
00:07:48,025 --> 00:07:50,126
Mount Gibbs, another unusually

224
00:07:50,227 --> 00:07:51,661
colored mountain in the northern

225
00:07:51,729 --> 00:07:54,831
reaches of the park.

226
00:07:54,932 --> 00:07:57,834
It lies above a layer of granite

227
00:07:57,901 --> 00:07:59,769
and is made from reddish-gray

228
00:07:59,837 --> 00:08:03,072
rock.

229
00:08:03,173 --> 00:08:05,141
Strangely, these rocks were

230
00:08:05,209 --> 00:08:06,743
also once molten.

231
00:08:06,844 --> 00:08:08,111
>> Here I have a rock from Mount

232
00:08:08,212 --> 00:08:10,280
Gibbs, and I can see that most

233
00:08:10,314 --> 00:08:11,581
of the crystals are very, very

234
00:08:11,649 --> 00:08:12,849
small. Most of them I can't

235
00:08:12,916 --> 00:08:14,017
even see.

236
00:08:14,118 --> 00:08:15,485
>> These small crystals tell

237
00:08:15,552 --> 00:08:18,021
an incredible story. When molten

238
00:08:18,088 --> 00:08:19,722
rock cools quickly in the open

239
00:08:19,757 --> 00:08:21,457
air, crystals don't have time

240
00:08:21,492 --> 00:08:23,259
to grow.

241
00:08:23,294 --> 00:08:24,294
>> What that tells me is that

242
00:08:24,361 --> 00:08:25,928
this is a volcanic rock that was

243
00:08:25,996 --> 00:08:29,766
spewed out at the surface.

244
00:08:29,833 --> 00:08:32,835
>> It is 200 million years ago.

245
00:08:32,936 --> 00:08:34,804
Volcanoes shatter the tranquil

246
00:08:34,838 --> 00:08:37,473
West coast. The earth explodes

247
00:08:37,574 --> 00:08:40,476
with molten rock. For the next

248
00:08:40,577 --> 00:08:42,945
100 million years, lava pours

249
00:08:43,013 --> 00:08:44,914
thick and fast onto the land,

250
00:08:44,948 --> 00:08:46,549
covering the sandstone in

251
00:08:46,583 --> 00:08:51,120
volcanic rock 10,000 feet high.

252
00:08:51,188 --> 00:08:54,023
It stretches for 400 miles along

253
00:08:54,124 --> 00:08:56,659
the coast.

254
00:08:56,760 --> 00:08:58,294
North America's greatest

255
00:08:58,395 --> 00:08:59,829
mountain chain--the mighty

256
00:08:59,897 --> 00:09:02,031
Sierra Nevada--is forming, and

257
00:09:02,099 --> 00:09:03,533
the area that would become

258
00:09:03,567 --> 00:09:05,268
Yosemite is caught right in the

259
00:09:05,302 --> 00:09:07,737
middle of it.

260
00:09:07,838 --> 00:09:10,073
But some of this rising, molten

261
00:09:10,107 --> 00:09:11,574
rock never makes it to the

262
00:09:11,642 --> 00:09:13,843
surface. Trapped beneath the

263
00:09:13,911 --> 00:09:15,645
blanket of mountains, it cools

264
00:09:15,713 --> 00:09:18,281
slowly, creating a giant chamber

265
00:09:18,349 --> 00:09:20,283
full of solidifying granite

266
00:09:20,351 --> 00:09:23,453
two miles below the surface.

267
00:09:23,487 --> 00:09:26,723
400 miles long, 60 miles wide,

268
00:09:26,757 --> 00:09:29,092
and 5 miles deep, it stretches

269
00:09:29,159 --> 00:09:31,094
along the entire spine of the

270
00:09:31,161 --> 00:09:33,262
Sierra Nevada mountain range.

271
00:09:33,297 --> 00:09:34,931
Yosemite's immense granite

272
00:09:34,998 --> 00:09:37,100
monoliths were forged in a fiery

273
00:09:37,201 --> 00:09:40,470
furnace two miles below ground.

274
00:09:40,537 --> 00:09:42,071
>> A hundred million years ago,

275
00:09:42,106 --> 00:09:43,806
I would have been standing in a

276
00:09:43,841 --> 00:09:46,109
vast chamber of molten rock,

277
00:09:46,210 --> 00:09:47,910
with rock rising thousands of

278
00:09:48,011 --> 00:09:51,481
feet above me.

279
00:09:51,548 --> 00:09:53,883
>> Scientists investigating how

280
00:09:53,951 --> 00:09:55,518
the rocks at Yosemite formed

281
00:09:55,586 --> 00:09:58,721
have found...

282
00:09:58,789 --> 00:10:01,057
bands of granite--evidence

283
00:10:01,158 --> 00:10:02,325
Yosemite's rocks were once

284
00:10:02,426 --> 00:10:04,327
molten...

285
00:10:04,428 --> 00:10:06,696
and volcanic rocks--proof that

286
00:10:06,797 --> 00:10:08,331
the granite formed deep beneath

287
00:10:08,399 --> 00:10:10,433
the earth.

288
00:10:10,501 --> 00:10:11,801
But scientists were still

289
00:10:11,869 --> 00:10:14,237
mystified. Yosemite granite is

290
00:10:14,304 --> 00:10:16,572
so strong, it's unlike granite

291
00:10:16,607 --> 00:10:18,775
anywhere else on earth.

292
00:10:18,809 --> 00:10:20,343
For hundreds of years, they

293
00:10:20,444 --> 00:10:21,978
tried to solve the mystery,

294
00:10:22,012 --> 00:10:23,946
while the answer was actually

295
00:10:23,981 --> 00:10:26,221
staring them in the face.

296
00:10:30,436 --> 00:10:32,370
>> 250 million years ago,

297
00:10:32,438 --> 00:10:34,105
Yosemite's landscape was a

298
00:10:34,173 --> 00:10:38,610
peaceful coastal plain.

299
00:10:38,644 --> 00:10:40,178
Now the investigation moves to

300
00:10:40,279 --> 00:10:42,280
100 million years ago.

301
00:10:42,348 --> 00:10:43,348
The land that would become

302
00:10:43,416 --> 00:10:45,717
Yosemite is in turmoil.

303
00:10:45,785 --> 00:10:47,485
Volcanoes dot the skyline,

304
00:10:47,520 --> 00:10:49,287
spilling mountains of lava onto

305
00:10:49,321 --> 00:10:52,057
the land.

306
00:10:55,061 --> 00:10:57,495
And entombed beneath two miles

307
00:10:57,563 --> 00:10:59,597
of volcanic rock lies Yosemite's

308
00:10:59,665 --> 00:11:01,599
molten granite.

309
00:11:01,667 --> 00:11:03,601
The next ten million years is a

310
00:11:03,669 --> 00:11:05,036
critical period for the rocks

311
00:11:05,137 --> 00:11:06,738
of Yosemite.

312
00:11:06,772 --> 00:11:08,306
Something unique is happening to

313
00:11:08,407 --> 00:11:10,208
the granite, making it tough

314
00:11:10,242 --> 00:11:12,410
enough to hold up cliffs 3,000

315
00:11:12,478 --> 00:11:16,681
feet high.

316
00:11:16,749 --> 00:11:18,049
The search for the secret of

317
00:11:18,117 --> 00:11:19,517
Yosemite granite's immense

318
00:11:19,585 --> 00:11:21,319
strength led scientists to the

319
00:11:21,387 --> 00:11:23,388
biggest steep-sided granite

320
00:11:23,422 --> 00:11:26,057
block in the world--the mighty

321
00:11:26,125 --> 00:11:28,760
El Capitan.

322
00:11:33,466 --> 00:11:35,033
Twice the height of the Empire

323
00:11:35,101 --> 00:11:37,669
State building, over 3 billion

324
00:11:37,736 --> 00:11:40,672
cubic feet of rock rises into

325
00:11:40,739 --> 00:11:46,478
the air.

326
00:11:46,512 --> 00:11:48,279
>> El Capitan is the largest

327
00:11:48,314 --> 00:11:49,781
Granite monolith in Yosemite

328
00:11:49,849 --> 00:11:51,683
National Park--3,000 feet of

329
00:11:51,784 --> 00:11:54,185
pure granite. It's one of the

330
00:11:54,220 --> 00:11:55,820
biggest cliffs in the world.

331
00:11:55,855 --> 00:11:57,055
When I look up at something like

332
00:11:57,123 --> 00:11:58,323
this, I really want to hang onto

333
00:11:58,390 --> 00:11:59,491
the rock because I feel like I'm

334
00:11:59,592 --> 00:12:00,758
going to fall backwards with

335
00:12:00,826 --> 00:12:03,862
vertigo. Amazing.

336
00:12:12,638 --> 00:12:14,873
>> El Capitan is the ultimate

337
00:12:14,940 --> 00:12:17,775
"big wall" climb. Once

338
00:12:17,843 --> 00:12:19,043
considered impossible to

339
00:12:19,111 --> 00:12:20,578
conquer, it's a treacherous

340
00:12:20,679 --> 00:12:22,480
ascent up a vertical, near

341
00:12:22,581 --> 00:12:25,016
featureless rock face, with only

342
00:12:25,050 --> 00:12:26,384
a handful of routes to the

343
00:12:26,418 --> 00:12:27,952
summit.

344
00:12:28,020 --> 00:12:30,021
Sheer granite walls are normally

345
00:12:30,122 --> 00:12:32,123
unstable and over time get

346
00:12:32,191 --> 00:12:34,559
pulled down by erosion, so it

347
00:12:34,593 --> 00:12:36,294
was a mystery how rocks could

348
00:12:36,395 --> 00:12:39,130
hold up cliffs this big.

349
00:12:39,198 --> 00:12:41,566
[rhythmic tapping]

350
00:12:41,634 --> 00:12:43,201
Scientists are sampling the

351
00:12:43,269 --> 00:12:45,136
rocks to find out, but the

352
00:12:45,204 --> 00:12:47,138
Yosemite granite doesn't give in

353
00:12:47,206 --> 00:12:49,307
without a fight.

354
00:12:49,408 --> 00:12:52,043
>> Whew! These Yosemite granites

355
00:12:52,111 --> 00:12:53,478
are really hard. You can work up

356
00:12:53,579 --> 00:12:54,679
quite a sweat trying to collect

357
00:12:54,747 --> 00:13:00,218
a bagful of this stuff.

358
00:13:00,286 --> 00:13:02,020
>> Buried within this rock is

359
00:13:02,121 --> 00:13:04,756
the secret to Yosemite granite's

360
00:13:04,823 --> 00:13:07,458
success.

361
00:13:07,493 --> 00:13:12,630
>> Oh, finally.

362
00:13:12,631 --> 00:13:14,399
Well, one clue to why these

363
00:13:14,466 --> 00:13:15,767
rocks are so tough is given by

364
00:13:15,834 --> 00:13:18,203
this sample right here.

365
00:13:18,204 --> 00:13:21,306
These are really large crystals.

366
00:13:21,373 --> 00:13:23,474
Large crystals make a rock

367
00:13:23,576 --> 00:13:24,475
really strong and they kind of

368
00:13:24,543 --> 00:13:25,643
weld together and they're

369
00:13:25,678 --> 00:13:27,011
flawless and they give a rock

370
00:13:27,079 --> 00:13:28,179
a lot of strength.

371
00:13:28,214 --> 00:13:29,480
>> But it was a mystery how

372
00:13:29,548 --> 00:13:31,082
these tough crystals got so

373
00:13:31,116 --> 00:13:33,384
large and created such flawless

374
00:13:33,485 --> 00:13:36,588
rocks.

375
00:13:36,655 --> 00:13:38,356
This is in contrast to normal

376
00:13:38,390 --> 00:13:40,191
granite, which, when it cools,

377
00:13:40,259 --> 00:13:42,493
forms a hard rock with a fatal

378
00:13:42,561 --> 00:13:45,129
flaw.

379
00:13:45,197 --> 00:13:46,931
Riddled with cracks, these rocks

380
00:13:46,999 --> 00:13:49,400
are vulnerable to erosion.

381
00:13:49,468 --> 00:13:50,935
>> If you take anything and it's

382
00:13:51,003 --> 00:13:52,103
very hot and you cool it

383
00:13:52,171 --> 00:13:55,373
quickly, it'll shatter.

384
00:13:55,441 --> 00:13:56,941
Granite bodies that cool

385
00:13:57,009 --> 00:13:58,543
quickly form a lot of cracks

386
00:13:58,577 --> 00:14:00,011
that weaken the rock body and

387
00:14:00,112 --> 00:14:01,913
make it unable to support

388
00:14:02,014 --> 00:14:03,748
3,000-foot cliffs.

389
00:14:03,849 --> 00:14:05,483
If you walk up to a typical

390
00:14:05,551 --> 00:14:06,718
granite and look at it, you'll

391
00:14:06,752 --> 00:14:08,453
find cracks a foot apart, two

392
00:14:08,487 --> 00:14:10,722
feet apart. If you walk up to

393
00:14:10,756 --> 00:14:11,889
El Capitan, you might have to

394
00:14:11,924 --> 00:14:13,625
go a hundred feet or more

395
00:14:13,659 --> 00:14:16,761
between cracks in the rock.

396
00:14:16,829 --> 00:14:18,263
>> Clearly, something different

397
00:14:18,297 --> 00:14:20,398
happened here 100 million years

398
00:14:20,466 --> 00:14:22,300
ago.

399
00:14:22,368 --> 00:14:24,569
>> El Capitan is really just one

400
00:14:24,670 --> 00:14:27,438
large, uniform, essentially

401
00:14:27,473 --> 00:14:29,474
faultless piece of granite, and

402
00:14:29,575 --> 00:14:31,009
that makes it very difficult for

403
00:14:31,076 --> 00:14:33,177
erosion to deal with.

404
00:14:33,212 --> 00:14:34,345
>> For many years, it was

405
00:14:34,380 --> 00:14:35,647
a puzzle what had caused

406
00:14:35,748 --> 00:14:37,348
Yosemite granite to form so

407
00:14:37,383 --> 00:14:39,617
differently. But the secret had

408
00:14:39,652 --> 00:14:41,386
been staring scientists in the

409
00:14:41,453 --> 00:14:43,021
face.

410
00:14:43,088 --> 00:14:44,188
>> One of the things you can see

411
00:14:44,256 --> 00:14:46,157
is a clue as to how this

412
00:14:46,191 --> 00:14:48,626
landscape formed in that dark,

413
00:14:48,661 --> 00:14:52,297
diagonal splotch.

414
00:14:52,364 --> 00:14:53,998
That's called the North American

415
00:14:54,066 --> 00:14:55,633
wall because that dark blob

416
00:14:55,668 --> 00:14:57,468
looks like, with some

417
00:14:57,569 --> 00:14:59,203
imagination, a map of North

418
00:14:59,271 --> 00:15:01,272
America and you can kind of see

419
00:15:01,373 --> 00:15:02,807
Baja California sticking down on

420
00:15:02,908 --> 00:15:04,742
the left side there and Alaska

421
00:15:04,843 --> 00:15:06,377
up to the northwest.

422
00:15:06,445 --> 00:15:07,845
And it's made up of a much

423
00:15:07,913 --> 00:15:09,480
darker, finer-grained rock

424
00:15:09,548 --> 00:15:10,815
like this.

425
00:15:10,916 --> 00:15:12,450
>> This dark granite is not just

426
00:15:12,551 --> 00:15:14,452
a map of North America.

427
00:15:14,553 --> 00:15:17,021
It's a window into the unique

428
00:15:17,089 --> 00:15:18,656
events that happened inside the

429
00:15:18,724 --> 00:15:20,458
Yosemite granite, when it was

430
00:15:20,559 --> 00:15:22,727
buried deep beneath the earth.

431
00:15:22,828 --> 00:15:24,195
>> And it's a younger body of

432
00:15:24,296 --> 00:15:26,464
granitic rock that filled a

433
00:15:26,532 --> 00:15:29,200
crack within the main body of

434
00:15:29,268 --> 00:15:31,903
El Capitan granite.

435
00:15:31,970 --> 00:15:34,472
>> 100 million years ago, the

436
00:15:34,540 --> 00:15:36,374
main body of granite cools and

437
00:15:36,475 --> 00:15:37,909
begins to harden beneath the

438
00:15:38,010 --> 00:15:40,511
earth.

439
00:15:40,546 --> 00:15:42,914
But then fresh, molten rock

440
00:15:42,981 --> 00:15:44,982
invades a crack and injects it

441
00:15:45,017 --> 00:15:46,918
with a blast of heat.

442
00:15:47,019 --> 00:15:49,153
The granite now takes ten times

443
00:15:49,188 --> 00:15:52,623
longer to cool. Huge, robust

444
00:15:52,725 --> 00:15:55,059
crystals form and reseal the

445
00:15:55,094 --> 00:15:57,695
defective cracks. Time after

446
00:15:57,730 --> 00:15:59,997
Time, fresh molten rock invades

447
00:16:00,099 --> 00:16:02,200
old, re-melting and welding

448
00:16:02,267 --> 00:16:04,635
the Yosemite granite, creating

449
00:16:04,703 --> 00:16:06,904
gigantic, shatterproof blocks

450
00:16:06,972 --> 00:16:08,806
which now tower thousands of

451
00:16:08,874 --> 00:16:11,642
feet into the air.

452
00:16:11,710 --> 00:16:13,611
>> Given that these are

453
00:16:13,645 --> 00:16:15,646
obviously very strong rocks,

454
00:16:15,714 --> 00:16:17,281
it puts the Whitney-Muir

455
00:16:17,349 --> 00:16:18,716
controversy in an interesting

456
00:16:18,784 --> 00:16:20,818
light, because Whitney wanted

457
00:16:20,886 --> 00:16:22,620
the rocks to have broken and for

458
00:16:22,721 --> 00:16:24,255
the valley to have fallen down

459
00:16:24,356 --> 00:16:26,457
in between a couple of major

460
00:16:26,558 --> 00:16:28,359
cracks. Muir wanted the whole

461
00:16:28,427 --> 00:16:30,461
thing to be carved by glaciers.

462
00:16:30,529 --> 00:16:31,462
And both of those seem really

463
00:16:31,530 --> 00:16:33,531
difficult, given how strong

464
00:16:33,599 --> 00:16:35,533
these rocks are, and yet behind

465
00:16:35,601 --> 00:16:36,934
me here is a 3,000-foot-deep

466
00:16:37,035 --> 00:16:39,637
valley. Something carved it.

467
00:16:46,178 --> 00:16:48,012
>> In the search to understand

468
00:16:48,113 --> 00:16:49,947
why Yosemite granite is so

469
00:16:50,015 --> 00:16:54,018
strong, scientists have found...

470
00:16:54,086 --> 00:16:56,220
large granite crystals welded

471
00:16:56,288 --> 00:16:57,855
together to form a tough,

472
00:16:57,923 --> 00:17:00,491
flawless rock, and the North

473
00:17:00,559 --> 00:17:02,260
America wall--evidence that

474
00:17:02,294 --> 00:17:03,928
Yosemite granite was reheated

475
00:17:03,996 --> 00:17:06,531
time after time, creating huge,

476
00:17:06,565 --> 00:17:09,300
faultless blocks.

477
00:17:09,401 --> 00:17:10,835
100 million years ago,

478
00:17:10,936 --> 00:17:12,904
Yosemite's granite lies buried

479
00:17:12,938 --> 00:17:14,539
beneath a volcanic mountain

480
00:17:14,573 --> 00:17:17,074
range two miles high.

481
00:17:17,109 --> 00:17:18,943
Rivers slice into this soft

482
00:17:19,011 --> 00:17:20,945
volcanic roof, gouging and

483
00:17:21,013 --> 00:17:22,847
washing it away.

484
00:17:22,915 --> 00:17:25,850
Then, 60 million years ago, when

485
00:17:25,918 --> 00:17:27,652
Dinosaurs are no more, the

486
00:17:27,719 --> 00:17:29,487
featureless lump of Yosemite

487
00:17:29,555 --> 00:17:31,389
granite is finally exposed to

488
00:17:31,490 --> 00:17:33,491
the elements.

489
00:17:33,559 --> 00:17:35,193
But Yosemite's ultra-tough

490
00:17:35,260 --> 00:17:37,295
granite defies attack.

491
00:17:37,396 --> 00:17:39,630
For another 50 million years,

492
00:17:39,665 --> 00:17:42,300
it remains unscathed.

493
00:17:42,367 --> 00:17:44,469
It would take a catastrophic

494
00:17:44,570 --> 00:17:47,472
event to chisel the 3,000-foot

495
00:17:47,573 --> 00:17:48,906
Canyon out of one of the

496
00:17:48,941 --> 00:17:51,556
toughest rocks on earth.

497
00:17:55,654 --> 00:17:57,021
>> Yosemite's Merced River

498
00:17:57,122 --> 00:18:00,925
meanders in a 3,000-foot canyon.

499
00:18:00,993 --> 00:18:03,928
But 250 million years ago,

500
00:18:03,996 --> 00:18:08,299
no vast canyon stood here.

501
00:18:08,367 --> 00:18:10,735
Yosemite is a flat coastal

502
00:18:10,802 --> 00:18:12,837
plain. It is blasted by

503
00:18:12,938 --> 00:18:14,939
volcanoes, and its granite is

504
00:18:15,007 --> 00:18:16,807
buried beneath two miles of

505
00:18:16,842 --> 00:18:19,277
volcanic rock.

506
00:18:19,378 --> 00:18:20,645
When the Yosemite granite is

507
00:18:20,746 --> 00:18:22,513
finally exposed, it is

508
00:18:22,648 --> 00:18:23,915
a shallow, run-of-the-mill

509
00:18:23,982 --> 00:18:25,516
river valley.

510
00:18:25,584 --> 00:18:27,618
For a staggering 50 million

511
00:18:27,719 --> 00:18:29,887
years, it defies the destructive

512
00:18:29,955 --> 00:18:32,256
powers of erosion.

513
00:18:32,324 --> 00:18:33,891
If scientists were going to

514
00:18:33,959 --> 00:18:35,159
solve the mystery of how

515
00:18:35,260 --> 00:18:36,961
Yosemite valley formed, they'd

516
00:18:37,062 --> 00:18:38,596
have to investigate the pivotal

517
00:18:38,630 --> 00:18:40,898
moment 7 million years ago when

518
00:18:40,966 --> 00:18:43,501
a 3,000-foot canyon was suddenly

519
00:18:43,535 --> 00:18:45,870
chiseled into the granite, one

520
00:18:45,971 --> 00:18:48,506
of the toughest rocks on earth.

521
00:18:48,607 --> 00:18:50,675
A clue to what almighty force

522
00:18:50,709 --> 00:18:52,610
overpowered the Yosemite granite

523
00:18:52,711 --> 00:18:54,211
lies high up on the exposed

524
00:18:54,246 --> 00:18:57,782
cliffs--strange, deep cracks

525
00:18:57,849 --> 00:18:59,317
running for hundreds of feet

526
00:18:59,351 --> 00:19:01,786
through the rock.

527
00:19:01,887 --> 00:19:03,120
>> Yosemite's granites are

528
00:19:03,155 --> 00:19:04,221
strong, but they're not always

529
00:19:04,256 --> 00:19:06,424
strong. I'm standing on a fin of

530
00:19:06,491 --> 00:19:08,693
rock between two deep fissures.

531
00:19:08,694 --> 00:19:10,328
These cracks run right across

532
00:19:10,429 --> 00:19:12,597
the Yosemite landscape, and they

533
00:19:12,664 --> 00:19:14,198
clearly formed after the

534
00:19:14,266 --> 00:19:15,733
granite formed.

535
00:19:15,734 --> 00:19:16,634
And if I look at their

536
00:19:16,668 --> 00:19:18,669
orientation...

537
00:19:18,770 --> 00:19:23,274
they all go to the northeast.

538
00:19:23,308 --> 00:19:25,209
>> Strangely, Yosemite valley is

539
00:19:25,277 --> 00:19:27,311
also oriented along the same

540
00:19:27,379 --> 00:19:28,946
northeast-southwesterly

541
00:19:29,014 --> 00:19:31,015
direction.

542
00:19:31,116 --> 00:19:32,717
Perhaps these cracks were the

543
00:19:32,751 --> 00:19:34,285
remnants of a cataclysmic

544
00:19:34,386 --> 00:19:35,853
rock-splitting event, as

545
00:19:35,921 --> 00:19:38,489
Josiah Whitney had predicted.

546
00:19:38,557 --> 00:19:40,458
A respected, Yale-educated

547
00:19:40,492 --> 00:19:41,759
scientist, he passionately

548
00:19:41,827 --> 00:19:44,095
believed titanic forces beneath

549
00:19:44,129 --> 00:19:45,830
Yosemite had pulled the land

550
00:19:45,931 --> 00:19:47,832
apart, causing it to collapse

551
00:19:47,933 --> 00:19:49,400
along gigantic fault-line

552
00:19:49,468 --> 00:19:51,669
cracks.

553
00:19:51,737 --> 00:19:53,204
Could it be that the argument

554
00:19:53,271 --> 00:19:54,672
was swinging in the bombastic

555
00:19:54,740 --> 00:19:56,641
Whitney's favor, and Muir's

556
00:19:56,675 --> 00:19:58,476
glacial theory was the rambling

557
00:19:58,543 --> 00:19:59,910
of an ignorant shepherd after

558
00:19:59,945 --> 00:20:02,680
all? Scientists searching for

559
00:20:02,714 --> 00:20:03,881
the answers as to how these

560
00:20:03,982 --> 00:20:06,517
giant cracks formed used modern

561
00:20:06,618 --> 00:20:08,085
technology to take a closer

562
00:20:08,153 --> 00:20:09,954
look at the ground beneath the

563
00:20:09,988 --> 00:20:11,689
Sierra Nevada.

564
00:20:11,723 --> 00:20:12,857
They did not find evidence of

565
00:20:12,891 --> 00:20:14,625
Whitney's cataclysmic rifting

566
00:20:14,726 --> 00:20:16,360
valley, but discovered

567
00:20:16,428 --> 00:20:18,529
a catastrophic event which had

568
00:20:18,597 --> 00:20:20,598
ramifications on a far greater

569
00:20:20,632 --> 00:20:22,667
scale.

570
00:20:22,734 --> 00:20:24,301
Seismic evidence has revealed

571
00:20:24,369 --> 00:20:25,870
that the earth's crust is made

572
00:20:25,937 --> 00:20:28,105
of layers. The lighter outer

573
00:20:28,140 --> 00:20:30,141
shell forms the land, but

574
00:20:30,208 --> 00:20:32,309
fastened beneath is a dense

575
00:20:32,411 --> 00:20:34,845
anchor of sturdy rock.

576
00:20:34,913 --> 00:20:36,414
And beneath the Sierra Nevada,

577
00:20:36,481 --> 00:20:38,049
scientists discovered something

578
00:20:38,116 --> 00:20:40,685
extraordinary--a huge section of

579
00:20:40,752 --> 00:20:43,554
this lower crust, 200 miles long

580
00:20:43,655 --> 00:20:47,291
and 40 miles wide, is missing.

581
00:20:47,325 --> 00:20:49,927
>> This model represents the

582
00:20:49,961 --> 00:20:51,762
Sierra Nevada as it looked ten

583
00:20:51,830 --> 00:20:52,830
million years ago.

584
00:20:52,831 --> 00:20:54,231
So the top here represents the

585
00:20:54,299 --> 00:20:55,666
mountain range. The bottom

586
00:20:55,767 --> 00:20:57,501
there, it represents the lower

587
00:20:57,569 --> 00:20:58,569
crust.

588
00:20:58,570 --> 00:21:00,037
Sometime in the past ten million

589
00:21:00,138 --> 00:21:02,373
years, part of that lower crust

590
00:21:02,407 --> 00:21:03,841
disconnected from the mountain

591
00:21:03,909 --> 00:21:07,411
range and dropped away.

592
00:21:07,479 --> 00:21:09,914
The end result is that there was

593
00:21:09,948 --> 00:21:11,282
uplift of the Sierra Nevada

594
00:21:11,316 --> 00:21:12,216
because they were being held

595
00:21:12,284 --> 00:21:14,118
down by those dense rocks. So

596
00:21:14,186 --> 00:21:15,286
there was uplift of the Sierra

597
00:21:15,320 --> 00:21:16,554
Nevada, but because most of the

598
00:21:16,588 --> 00:21:18,089
root fell away to the east, the

599
00:21:18,123 --> 00:21:19,557
whole mountain range, rather

600
00:21:19,591 --> 00:21:21,292
than bobbing straight up, tilted

601
00:21:21,359 --> 00:21:23,494
to the west.

602
00:21:23,562 --> 00:21:25,730
>> 7 million years ago, a huge

603
00:21:25,764 --> 00:21:27,298
chunk of the lower crust

604
00:21:27,399 --> 00:21:29,133
suddenly drops away.

605
00:21:29,201 --> 00:21:31,302
The entire mountain chain snaps

606
00:21:31,369 --> 00:21:32,770
along its spine and tilts

607
00:21:32,838 --> 00:21:35,773
upward. Finally, here is a force

608
00:21:35,841 --> 00:21:37,675
capable of overcoming Yosemite's

609
00:21:37,743 --> 00:21:42,113
ultra-tough granite.

610
00:21:42,214 --> 00:21:44,381
As it snaps, the enormous

611
00:21:44,483 --> 00:21:45,916
pressure cracks the solid

612
00:21:45,951 --> 00:21:47,852
granite along the entire length

613
00:21:47,953 --> 00:21:49,954
of the mountain range.

614
00:21:50,021 --> 00:21:51,555
But it was a mystery how these

615
00:21:51,656 --> 00:21:53,190
cracks could give rise to

616
00:21:53,225 --> 00:21:55,860
a 3,000-foot-deep canyon.

617
00:21:55,927 --> 00:21:58,262
Scientists realized some other

618
00:21:58,296 --> 00:21:59,930
force must have attacked the

619
00:22:00,031 --> 00:22:02,199
weakened, vulnerable granite.

620
00:22:02,300 --> 00:22:03,934
The hunt was on for an

621
00:22:04,002 --> 00:22:06,537
accomplice...

622
00:22:06,571 --> 00:22:08,205
and 5 miles downstream of

623
00:22:08,273 --> 00:22:10,641
Yosemite, at El Portal, they

624
00:22:10,675 --> 00:22:14,311
find it.

625
00:22:14,379 --> 00:22:18,482
Rapids.

626
00:22:18,550 --> 00:22:21,218
Here, Yosemite's meandering

627
00:22:21,286 --> 00:22:23,287
Merced River has transformed

628
00:22:23,355 --> 00:22:26,757
Into a raging torrent.

629
00:22:26,825 --> 00:22:29,894
At times, 1,000 cubic feet of

630
00:22:29,928 --> 00:22:31,228
water gush through this narrow

631
00:22:31,296 --> 00:22:34,298
gorge every second, creating

632
00:22:34,366 --> 00:22:36,667
treacherous waves and turbulent

633
00:22:36,735 --> 00:22:40,805
eddies.

634
00:22:40,839 --> 00:22:42,940
>> So this is the Merced River,

635
00:22:43,008 --> 00:22:44,542
about 5 miles downstream of

636
00:22:44,576 --> 00:22:45,843
Yosemite valley.

637
00:22:45,911 --> 00:22:47,845
It's extremely powerful. It's

638
00:22:47,913 --> 00:22:50,748
a series of rapids and cascades

639
00:22:50,849 --> 00:22:52,483
over these boulders, and there's

640
00:22:52,551 --> 00:22:54,285
a lot of energy being expended

641
00:22:54,352 --> 00:22:55,986
by this river right now.

642
00:22:56,021 --> 00:22:57,621
>> Scientists realized this

643
00:22:57,656 --> 00:22:59,723
ferocious force, combined with

644
00:22:59,758 --> 00:23:01,559
the rock-weakening cracks, even

645
00:23:01,626 --> 00:23:03,194
had the power to cut into

646
00:23:03,261 --> 00:23:04,829
Yosemite's granite.

647
00:23:04,896 --> 00:23:06,030
>> The erosion of the river is

648
00:23:06,097 --> 00:23:07,364
focused right along the river

649
00:23:07,465 --> 00:23:09,733
bed, and so it will cut down

650
00:23:09,835 --> 00:23:12,203
like a saw blade into the rock,

651
00:23:12,270 --> 00:23:13,838
about the width of the river.

652
00:23:13,905 --> 00:23:15,105
So as it does that, it will come

653
00:23:15,173 --> 00:23:16,841
down and steepen the valley

654
00:23:16,942 --> 00:23:19,276
walls. Those walls will become

655
00:23:19,344 --> 00:23:21,378
unstable, and there will be

656
00:23:21,446 --> 00:23:22,646
landslides into the river.

657
00:23:22,747 --> 00:23:23,647
The river will wash away the

658
00:23:23,715 --> 00:23:25,649
material, and you'll be back to

659
00:23:25,750 --> 00:23:27,384
that "V" shape.

660
00:23:27,452 --> 00:23:29,186
>> Scientists realized, if the

661
00:23:29,287 --> 00:23:30,988
Merced River created this deep,

662
00:23:31,022 --> 00:23:33,290
V-shaped canyon, then it could

663
00:23:33,358 --> 00:23:35,426
also have cut a deep Yosemite

664
00:23:35,460 --> 00:23:37,995
Valley.

665
00:23:43,468 --> 00:23:45,369
7 million years ago, as the

666
00:23:45,470 --> 00:23:47,571
Sierra Nevada tilts upwards, the

667
00:23:47,639 --> 00:23:49,707
mountain slope gets 3 times

668
00:23:49,741 --> 00:23:51,642
steeper, and the western-flowing

669
00:23:51,710 --> 00:23:53,177
Merced River surges with

670
00:23:53,278 --> 00:23:55,246
a torrent of water.

671
00:23:55,280 --> 00:23:57,381
Like a saw blade, it zigzags

672
00:23:57,449 --> 00:23:59,183
along the path of weakened,

673
00:23:59,284 --> 00:24:01,252
cracked granite.

674
00:24:01,286 --> 00:24:03,087
In less than 5 million years,

675
00:24:03,154 --> 00:24:05,723
it cuts a 3,000-foot, v-shaped

676
00:24:05,824 --> 00:24:07,625
canyon running straight through

677
00:24:07,726 --> 00:24:10,995
the heart of Yosemite.

678
00:24:11,062 --> 00:24:13,097
Scientists investigating how

679
00:24:13,198 --> 00:24:14,899
Yosemite's deep canyon formed

680
00:24:15,000 --> 00:24:17,101
have discovered...

681
00:24:17,168 --> 00:24:20,004
strange cracks in the rock--

682
00:24:20,105 --> 00:24:21,805
proof that the up-lifting Sierra

683
00:24:21,840 --> 00:24:24,742
Nevada weakened the granite...

684
00:24:24,809 --> 00:24:27,378
and rapids downstream--evidence

685
00:24:27,445 --> 00:24:28,646
that the Merced River cut a

686
00:24:28,713 --> 00:24:31,982
deep, V-shaped Yosemite canyon.

687
00:24:32,017 --> 00:24:33,550
But one part of the riddle

688
00:24:33,618 --> 00:24:36,887
remained unsolved...

689
00:24:36,922 --> 00:24:39,290
Yosemite's unique, box-like

690
00:24:39,357 --> 00:24:41,892
shape.

691
00:24:41,927 --> 00:24:44,328
Some other extraordinary force

692
00:24:44,362 --> 00:24:45,996
had caused the canyon walls to

693
00:24:46,097 --> 00:24:47,998
collapse and the valley floor

694
00:24:48,099 --> 00:24:49,600
to flatten.

695
00:24:49,634 --> 00:24:51,368
The controversy about how this

696
00:24:51,436 --> 00:24:54,785
strange canyon formed raged on.

697
00:25:26,673 --> 00:25:28,608
>> Yosemite has had a turbulent

698
00:25:28,675 --> 00:25:32,044
past. 200 million years ago, its

699
00:25:32,145 --> 00:25:34,580
coastal plain is shattered by

700
00:25:34,648 --> 00:25:37,650
volcanoes. And then, 7 million

701
00:25:37,751 --> 00:25:39,552
years ago, the Merced River

702
00:25:39,653 --> 00:25:41,254
suddenly carves a deep,

703
00:25:41,288 --> 00:25:43,656
V-shaped Yosemite valley.

704
00:25:43,724 --> 00:25:45,524
For the next 4 million years,

705
00:25:45,559 --> 00:25:47,627
the river runs in this narrow

706
00:25:47,661 --> 00:25:51,297
canyon. But then, Yosemite is

707
00:25:51,365 --> 00:25:55,735
radically transformed again.

708
00:25:55,802 --> 00:25:57,336
>> About two and a half million

709
00:25:57,371 --> 00:25:58,871
years ago, when our ancestors

710
00:25:58,972 --> 00:26:00,206
Were beginning to evolve in

711
00:26:00,274 --> 00:26:02,842
Africa, the v-shaped valley that

712
00:26:02,843 --> 00:26:04,911
was here began to evolve into

713
00:26:04,978 --> 00:26:06,812
the present valley floor, which

714
00:26:06,914 --> 00:26:08,881
Is flat, and is bounded by these

715
00:26:08,882 --> 00:26:10,516
vertical, sheer rock walls

716
00:26:10,550 --> 00:26:12,018
on its side.

717
00:26:12,085 --> 00:26:13,653
>> It was during this second

718
00:26:13,720 --> 00:26:15,354
extraordinary stage of cliff

719
00:26:15,455 --> 00:26:17,189
formation that the most iconic

720
00:26:17,291 --> 00:26:19,158
rock in America formed--

721
00:26:19,192 --> 00:26:21,928
Half Dome.

722
00:26:21,995 --> 00:26:23,696
This natural wonder's unique

723
00:26:23,730 --> 00:26:25,431
shape has intrigued people for

724
00:26:25,465 --> 00:26:27,266
centuries.

725
00:26:27,367 --> 00:26:29,735
Its enormous granite dome is

726
00:26:29,803 --> 00:26:31,904
over 3 billion cubic feet in

727
00:26:32,005 --> 00:26:35,174
size, as large as 1,000 football

728
00:26:35,242 --> 00:26:37,543
stadiums, and its striking

729
00:26:37,644 --> 00:26:40,179
northwest face is a 2,000-foot

730
00:26:40,280 --> 00:26:43,549
vertical drop.

731
00:26:43,617 --> 00:26:46,719
In 1870, amateur geologist John

732
00:26:46,820 --> 00:26:48,521
Muir had a radical theory about

733
00:26:48,555 --> 00:26:50,523
how Half Dome and Yosemite's

734
00:26:50,557 --> 00:26:52,892
other vast cliffs formed.

735
00:26:52,993 --> 00:26:54,460
He believed that thousands of

736
00:26:54,528 --> 00:26:55,695
years ago, the earth's

737
00:26:55,729 --> 00:26:57,196
temperature had plummeted and

738
00:26:57,264 --> 00:26:58,331
the valley had been filled with

739
00:26:58,398 --> 00:27:00,199
ice.

740
00:27:00,200 --> 00:27:01,233
>> You know, one thing that's

741
00:27:01,301 --> 00:27:02,435
important to keep in mind about

742
00:27:02,502 --> 00:27:04,971
John Muir, he didn't come up

743
00:27:04,972 --> 00:27:06,839
with this idea overnight. He was

744
00:27:06,873 --> 00:27:08,574
trekking, hiking, walking, going

745
00:27:08,608 --> 00:27:09,709
up to the tops of mountains. And

746
00:27:09,776 --> 00:27:10,943
the entire time he was doing

747
00:27:10,978 --> 00:27:12,311
this, he was listening, he was

748
00:27:12,346 --> 00:27:13,412
seeing, he was feeling, he was

749
00:27:13,513 --> 00:27:15,247
touching. And so he was slowly,

750
00:27:15,315 --> 00:27:17,583
letter by letter, word by word,

751
00:27:17,684 --> 00:27:19,318
learning the language of

752
00:27:19,386 --> 00:27:22,221
Yosemite.

753
00:27:22,322 --> 00:27:24,056
>> Muir knew from research in

754
00:27:24,124 --> 00:27:25,691
the european Alps that glaciers

755
00:27:25,792 --> 00:27:27,159
were capable of gouging out

756
00:27:27,227 --> 00:27:29,128
solid rock.

757
00:27:29,229 --> 00:27:30,763
As these great rivers of ice

758
00:27:30,864 --> 00:27:32,698
flow downhill, they press down

759
00:27:32,766 --> 00:27:34,133
on the canyon walls with a

760
00:27:34,201 --> 00:27:36,569
weight equal to 200 trucks per

761
00:27:36,603 --> 00:27:39,305
square yard, ripping out chunks

762
00:27:39,339 --> 00:27:41,307
of rock and causing the valley

763
00:27:41,341 --> 00:27:43,976
walls to get steeper.

764
00:27:44,044 --> 00:27:45,745
>> In general, glaciers

765
00:27:45,779 --> 00:27:48,047
transform a v-shaped valley that

766
00:27:48,115 --> 00:27:49,315
we see as characteristic of a

767
00:27:49,416 --> 00:27:51,784
river into a u-shaped valley

768
00:27:51,852 --> 00:27:54,286
by focusing their erosion on the

769
00:27:54,321 --> 00:27:56,389
valley walls, rather than on the

770
00:27:56,423 --> 00:27:58,858
valley bottom, until it has

771
00:27:58,925 --> 00:28:00,626
reached this "u" shape, at which

772
00:28:00,694 --> 00:28:02,762
point it can then continue to

773
00:28:02,829 --> 00:28:04,964
erode as that "u" shape.

774
00:28:05,032 --> 00:28:06,599
>> Muir knew that as a glacier

775
00:28:06,666 --> 00:28:08,467
flows, it grinds and polishes

776
00:28:08,502 --> 00:28:10,669
the bedrock with rough shards

777
00:28:10,737 --> 00:28:13,305
of rock lodged at its base.

778
00:28:13,373 --> 00:28:15,207
As they melt and disappear,

779
00:28:15,242 --> 00:28:17,576
glaciers leave behind u-shaped

780
00:28:17,644 --> 00:28:19,979
valleys and distinctiv

781
00:28:20,013 --> 00:28:24,183
scratch marks.

782
00:28:24,284 --> 00:28:26,185
Muir proposed that giant rivers

783
00:28:26,253 --> 00:28:28,187
of ice also once flowed through

784
00:28:28,288 --> 00:28:30,456
Yosemite valley.

785
00:28:30,557 --> 00:28:32,191
He hunted high and low for

786
00:28:32,259 --> 00:28:33,826
evidence of glacial scratch

787
00:28:33,927 --> 00:28:35,661
marks and eventually found a

788
00:28:35,729 --> 00:28:38,197
small, 20-foot square patch of

789
00:28:38,265 --> 00:28:40,332
rock 30 feet from the valley

790
00:28:40,367 --> 00:28:42,368
floor.

791
00:28:42,469 --> 00:28:44,336
>> The granite has scratches on

792
00:28:44,371 --> 00:28:46,439
its surface. Each one of these

793
00:28:46,473 --> 00:28:48,340
scratches is associated with

794
00:28:48,375 --> 00:28:50,009
a rock embedded in the sole

795
00:28:50,110 --> 00:28:52,978
of a glacier. I can imagine Muir

796
00:28:53,013 --> 00:28:55,514
claiming that this is

797
00:28:55,549 --> 00:28:57,083
irrefutable evidence of glacial

798
00:28:57,184 --> 00:28:59,251
occupation of the valley floor.

799
00:28:59,286 --> 00:29:00,820
>> But if glaciers ploughed down

800
00:29:00,921 --> 00:29:02,488
the valley, why weren't there

801
00:29:02,556 --> 00:29:04,090
millions of scratch marks on

802
00:29:04,157 --> 00:29:06,158
the cliffs?

803
00:29:06,193 --> 00:29:08,894
If Muir was correct, this is

804
00:29:08,995 --> 00:29:11,730
a picture of what happened.

805
00:29:11,798 --> 00:29:13,199
Two and a half million years

806
00:29:13,266 --> 00:29:15,634
ago, the temperature plummets.

807
00:29:15,702 --> 00:29:17,803
Yosemite valley fills to the

808
00:29:17,904 --> 00:29:20,639
brim with a gigantic glacier.

809
00:29:20,740 --> 00:29:22,541
Only the tallest mountains peek

810
00:29:22,642 --> 00:29:25,244
above the sea of ice.

811
00:29:25,278 --> 00:29:26,712
For thousands of years, the

812
00:29:26,813 --> 00:29:28,347
glacier grinds away at the

813
00:29:28,381 --> 00:29:30,449
granite walls, scratching the

814
00:29:30,517 --> 00:29:32,151
cliffs and undercutting a peak

815
00:29:32,185 --> 00:29:34,153
that will become Half Dome.

816
00:29:34,187 --> 00:29:36,188
When it retreats, the glacier

817
00:29:36,256 --> 00:29:37,990
leaves precarious slabs of

818
00:29:38,058 --> 00:29:40,159
overhanging rock.

819
00:29:40,193 --> 00:29:41,527
The unstable rock face crashes

820
00:29:41,628 --> 00:29:47,633
to the valley floor...

821
00:29:47,734 --> 00:29:50,102
cleaving the great northwest

822
00:29:50,170 --> 00:29:53,706
face of Half Dome.

823
00:29:53,740 --> 00:29:55,341
In the same way, subsequent

824
00:29:55,375 --> 00:29:57,009
smaller glaciers cut away at

825
00:29:57,077 --> 00:29:58,444
the base of the valley for two

826
00:29:58,545 --> 00:30:02,281
million years, cleaving sheer,

827
00:30:02,315 --> 00:30:04,250
vertical cliffs and removing all

828
00:30:04,284 --> 00:30:07,720
traces of glacial scratch marks.

829
00:30:07,787 --> 00:30:09,421
But there was still one

830
00:30:09,456 --> 00:30:11,457
glaringly obvious problem with

831
00:30:11,525 --> 00:30:13,726
Muir's theory, and arch enemy

832
00:30:13,793 --> 00:30:15,261
geologist Josiah Whitney

833
00:30:15,328 --> 00:30:17,163
pounced on it.

834
00:30:17,230 --> 00:30:18,898
If glaciers had carved the

835
00:30:18,965 --> 00:30:21,367
valley, why was Yosemite

836
00:30:21,434 --> 00:30:24,069
uniquely box-shaped and not

837
00:30:24,137 --> 00:30:25,704
U-shaped, like a classic

838
00:30:25,805 --> 00:30:27,907
glacial valley?

839
00:30:27,974 --> 00:30:29,909
Whitney attacked Muir's theory

840
00:30:29,976 --> 00:30:31,443
and stubbornly declared this

841
00:30:31,511 --> 00:30:33,245
square, flat-bottomed valley

842
00:30:33,280 --> 00:30:35,347
could only have formed if the

843
00:30:35,415 --> 00:30:38,350
bottom had fallen out.

844
00:30:38,418 --> 00:30:40,619
>> Whitney hypothesized that

845
00:30:40,720 --> 00:30:42,988
instead of being carved by

846
00:30:43,056 --> 00:30:44,223
glaciers that this was a

847
00:30:44,257 --> 00:30:46,358
fault-bounded valley with the

848
00:30:46,426 --> 00:30:48,327
valley walls being faults down

849
00:30:48,361 --> 00:30:51,163
which the block in between the

850
00:30:51,264 --> 00:30:55,634
valley walls has dropped.

851
00:30:55,702 --> 00:30:57,403
In Whitney's theory, the flat

852
00:30:57,437 --> 00:30:58,871
valley floor would be the top

853
00:30:58,905 --> 00:31:02,341
of the down-dropped block.

854
00:31:02,409 --> 00:31:04,343
>> Iin the quest to unravel the

855
00:31:04,444 --> 00:31:05,711
mystery of Yosemite's

856
00:31:05,812 --> 00:31:07,980
flat-bottomed canyon, scientists

857
00:31:08,048 --> 00:31:09,615
are investigating the valley

858
00:31:09,683 --> 00:31:12,785
floor.

859
00:31:12,886 --> 00:31:14,720
>> The kind of sediment that I

860
00:31:14,788 --> 00:31:17,156
see in this cut bank are coarse

861
00:31:17,224 --> 00:31:19,325
grains, pebbles, and sand--the

862
00:31:19,359 --> 00:31:21,126
same kind of rocks and sediment

863
00:31:21,161 --> 00:31:22,895
that the present stream can

864
00:31:22,963 --> 00:31:26,065
carry. In contrast to that, the

865
00:31:26,166 --> 00:31:31,403
deposit I see at my feet...

866
00:31:31,438 --> 00:31:33,539
is very fine-grained.

867
00:31:33,607 --> 00:31:35,808
>> Light, fine grained sediment

868
00:31:35,875 --> 00:31:37,776
like this is easily carried by

869
00:31:37,811 --> 00:31:40,145
flowing water. But when a river

870
00:31:40,247 --> 00:31:42,147
hits a body of still water, its

871
00:31:42,215 --> 00:31:44,049
energy levels slump, and it

872
00:31:44,084 --> 00:31:45,985
dumps its load.

873
00:31:46,052 --> 00:31:47,253
>> This the kind of sediment

874
00:31:47,354 --> 00:31:48,854
that we would expect to see on

875
00:31:48,888 --> 00:31:51,156
the floor of a lake.

876
00:31:51,224 --> 00:31:52,791
>> Further research has found

877
00:31:52,892 --> 00:31:54,693
similar strange sediments all

878
00:31:54,761 --> 00:31:56,528
over Yosemite.

879
00:31:56,596 --> 00:31:59,064
It's proof that 10,000 years

880
00:31:59,165 --> 00:32:01,133
ago, an ancient lake drowned

881
00:32:01,167 --> 00:32:03,769
this entire valley.

882
00:32:03,803 --> 00:32:04,770
Starting at the head of the

883
00:32:04,804 --> 00:32:07,072
canyon, it stretched for 5 miles

884
00:32:07,140 --> 00:32:09,408
through the landscape.

885
00:32:09,442 --> 00:32:11,043
But it was a mystery how Lake

886
00:32:11,077 --> 00:32:13,245
Yosemite had formed.

887
00:32:13,346 --> 00:32:14,980
Scientists scoured the valley

888
00:32:15,048 --> 00:32:16,849
looking for answers, and near

889
00:32:16,883 --> 00:32:18,784
the base of El Capitan at the

890
00:32:18,852 --> 00:32:20,519
farthest end of the valley,

891
00:32:20,620 --> 00:32:21,854
they stumbled upon an

892
00:32:21,888 --> 00:32:24,156
insignificant-looking ridge.

893
00:32:24,224 --> 00:32:26,525
It's an important clue to how

894
00:32:26,593 --> 00:32:28,160
Lake Yosemite and the valley

895
00:32:28,228 --> 00:32:31,497
formed. This mound is made of an

896
00:32:31,531 --> 00:32:33,499
unusual collection of rocks,

897
00:32:33,600 --> 00:32:35,668
And it runs from one side of

898
00:32:35,702 --> 00:32:39,238
the valley to the other.

899
00:32:39,306 --> 00:32:41,674
>> Given this arc of a ridge is

900
00:32:41,708 --> 00:32:43,976
just down from El Cap, one might

901
00:32:44,044 --> 00:32:45,110
expect that it could have been

902
00:32:45,145 --> 00:32:46,679
caused from a rock fall.

903
00:32:46,780 --> 00:32:50,983
But if you look around...

904
00:32:51,051 --> 00:32:53,585
that's not the case. Clearly,

905
00:32:53,620 --> 00:32:55,321
even in this local area, we have

906
00:32:55,388 --> 00:32:57,056
rocks that came from at least

907
00:32:57,123 --> 00:32:59,325
3 different places, no doubt, up

908
00:32:59,426 --> 00:33:01,060
the valley. This pink rock came

909
00:33:01,127 --> 00:33:02,594
from one portion of the valley,

910
00:33:02,696 --> 00:33:04,863
this gray granite came from

911
00:33:04,964 --> 00:33:06,765
another place. And this

912
00:33:06,866 --> 00:33:09,335
particular one, we can see the

913
00:33:09,402 --> 00:33:12,504
distinctive feldspars associated

914
00:33:12,605 --> 00:33:13,672
with the cathedral peaks

915
00:33:13,707 --> 00:33:15,407
granite.

916
00:33:15,475 --> 00:33:17,343
>> This strange distribution of

917
00:33:17,410 --> 00:33:19,311
rocks means that the ridge could

918
00:33:19,412 --> 00:33:20,612
not have formed from a

919
00:33:20,680 --> 00:33:22,781
catastrophic rock fall.

920
00:33:22,849 --> 00:33:25,317
Something else just as epic

921
00:33:25,385 --> 00:33:27,753
must have created it.

922
00:33:27,787 --> 00:33:30,956
This is a glacial moraine, the

923
00:33:31,057 --> 00:33:32,858
remnants of a glacier which once

924
00:33:32,926 --> 00:33:34,927
filled the valley. It's the

925
00:33:34,961 --> 00:33:36,595
conclusive evidence Muir had

926
00:33:36,663 --> 00:33:38,764
hoped for.

927
00:33:38,832 --> 00:33:41,500
Moraines form as glacial ice

928
00:33:41,601 --> 00:33:43,335
rips fragments of rock from the

929
00:33:43,403 --> 00:33:45,304
valley walls, carries them like

930
00:33:45,338 --> 00:33:46,972
a conveyor belt several miles

931
00:33:47,040 --> 00:33:49,241
downstream, and dumps the rubble

932
00:33:49,309 --> 00:33:51,944
at the mouth of the glacier.

933
00:33:52,011 --> 00:33:54,880
Scientists realized this ridge

934
00:33:54,948 --> 00:33:57,149
was also key to solving the

935
00:33:57,217 --> 00:33:59,284
mystery of how Lake Yosemite and

936
00:33:59,319 --> 00:34:01,120
the flat-bottomed valley floor

937
00:34:01,221 --> 00:34:02,955
formed.

938
00:34:03,056 --> 00:34:05,591
It wasn't just a moraine, it was

939
00:34:05,658 --> 00:34:08,394
a giant dam.

940
00:34:13,032 --> 00:34:14,500
It's two and a half million

941
00:34:14,567 --> 00:34:17,035
years ago, and glaciers grind

942
00:34:17,103 --> 00:34:19,772
through the valley. 10,000 years

943
00:34:19,873 --> 00:34:21,507
ago, the temperature rises and

944
00:34:21,574 --> 00:34:23,041
the glacier retreats.

945
00:34:23,109 --> 00:34:25,043
A huge moraine is dumped at the

946
00:34:25,145 --> 00:34:27,146
valley mouth, damming back the

947
00:34:27,213 --> 00:34:28,781
icy melt water.

948
00:34:28,848 --> 00:34:30,582
The entire valley floods,

949
00:34:30,650 --> 00:34:32,851
creating an enormous Lake

950
00:34:32,919 --> 00:34:34,420
Yosemite.

951
00:34:34,487 --> 00:34:36,755
Mountain streams spill into this

952
00:34:36,856 --> 00:34:38,657
still water and dump ton after

953
00:34:38,691 --> 00:34:41,293
ton of fine sediment.

954
00:34:41,327 --> 00:34:43,095
The lake chokes with silt,

955
00:34:43,163 --> 00:34:45,731
creating Yosemite's distinctive

956
00:34:45,832 --> 00:34:48,167
flat-bottomed valley floor.

957
00:34:48,201 --> 00:34:50,102
>> We know from seismic evidence

958
00:34:50,203 --> 00:34:51,970
collected in the 1930s that it's

959
00:34:52,005 --> 00:34:53,972
2,000 feet thick. That's enough

960
00:34:54,007 --> 00:34:55,607
sediment to cover New York City

961
00:34:55,642 --> 00:34:58,377
by a foot.

962
00:34:58,445 --> 00:35:00,279
>> And beneath this lake of

963
00:35:00,346 --> 00:35:01,747
sediment, they found the

964
00:35:01,815 --> 00:35:03,715
evidence that had always eluded

965
00:35:03,817 --> 00:35:06,618
Muir--a u-shaped basin, the

966
00:35:06,653 --> 00:35:08,821
hallmark of a classic glacial

967
00:35:08,888 --> 00:35:11,623
valley. It was indisputable

968
00:35:11,691 --> 00:35:13,559
evidence that Muir's intuitive

969
00:35:13,626 --> 00:35:15,260
Observations and seemingly

970
00:35:15,361 --> 00:35:16,962
far-fetched theory were

971
00:35:16,996 --> 00:35:19,898
correct, and the final nail in

972
00:35:19,999 --> 00:35:21,533
the coffin for Whitney's theory

973
00:35:21,634 --> 00:35:25,637
of a cataclysmic rifting valley.

974
00:35:25,705 --> 00:35:27,372
Scientists trying to understand

975
00:35:27,440 --> 00:35:28,807
how the steep cliffs and

976
00:35:28,908 --> 00:35:30,342
flat-bottomed valley formed

977
00:35:30,376 --> 00:35:32,544
have found...

978
00:35:32,645 --> 00:35:34,446
scratch marks--evidence that the

979
00:35:34,514 --> 00:35:35,781
sheer cliffs were carved by

980
00:35:35,815 --> 00:35:37,883
glaciers,

981
00:35:37,917 --> 00:35:39,785
and a glacial moraine--proof

982
00:35:39,819 --> 00:35:41,420
that an ancient Lake Yosemite

983
00:35:41,521 --> 00:35:42,788
filled with sediment and

984
00:35:42,856 --> 00:35:46,158
created the flat valley floor.

985
00:35:46,226 --> 00:35:47,926
For over two million years,

986
00:35:47,961 --> 00:35:49,428
the glaciers whittle away at

987
00:35:49,496 --> 00:35:52,865
Yosemite. Then 10,000 years ago,

988
00:35:52,966 --> 00:35:54,867
the glaciers retreat for good,

989
00:35:54,934 --> 00:35:56,502
Leaving the one-mile-wide

990
00:35:56,569 --> 00:35:58,871
Canyon we know today.

991
00:35:58,972 --> 00:36:00,672
But strange, dangerous forces

992
00:36:00,773 --> 00:36:02,508
are still exerting their power

993
00:36:02,609 --> 00:36:04,409
on Yosemite's landscape, with

994
00:36:04,477 --> 00:36:06,946
catastrophic consequences.

995
00:36:15,972 --> 00:36:17,172
>> Yosemite valley has been

996
00:36:17,240 --> 00:36:19,174
sculpted by torrential water and

997
00:36:19,242 --> 00:36:21,944
thick slabs of ice, but today

998
00:36:21,978 --> 00:36:23,979
another hidden force is shaping

999
00:36:24,080 --> 00:36:26,515
this magnificent landscape.

1000
00:36:26,616 --> 00:36:28,884
[loud rumbling]

1001
00:36:28,952 --> 00:36:33,622
It's 6:52 pm, July 10, 1996.

1002
00:36:33,690 --> 00:36:35,124
Yosemite is hit by

1003
00:36:35,158 --> 00:36:39,161
a catastrophic rock fall.

1004
00:36:39,262 --> 00:36:42,030
Within minutes, a huge dust

1005
00:36:42,065 --> 00:36:44,433
cloud of pulverized rock engulfs

1006
00:36:44,501 --> 00:36:47,236
the valley. News spreads that

1007
00:36:47,337 --> 00:36:49,304
Happy isles, the busiest trail

1008
00:36:49,339 --> 00:36:50,806
In the valley, has been

1009
00:36:50,874 --> 00:36:53,609
decimated. Yosemite is in

1010
00:36:53,710 --> 00:36:55,878
a state of emergency.

1011
00:36:55,879 --> 00:36:57,946
>> When I got here, the

1012
00:36:57,981 --> 00:37:00,516
devastation was really in full

1013
00:37:00,583 --> 00:37:03,252
force. I saw trees that were

1014
00:37:03,253 --> 00:37:04,686
just everywhere. There were

1015
00:37:04,754 --> 00:37:07,523
ambulances, and chaos just was

1016
00:37:07,624 --> 00:37:08,757
everywhere. People were running

1017
00:37:08,792 --> 00:37:10,325
around screaming, and the whole

1018
00:37:10,427 --> 00:37:12,261
area looked like a bomb had

1019
00:37:12,328 --> 00:37:13,796
gone off.

1020
00:37:13,897 --> 00:37:15,697
>> 80,000 tons of rock had

1021
00:37:15,799 --> 00:37:17,499
suddenly dislodged from the

1022
00:37:17,534 --> 00:37:19,067
cliff face.

1023
00:37:19,169 --> 00:37:20,936
>> The weight of 1,600 trucks

1024
00:37:20,970 --> 00:37:24,072
basically fell down. It hit and

1025
00:37:24,140 --> 00:37:26,842
then exploded, and it created

1026
00:37:26,876 --> 00:37:28,043
a windblast.

1027
00:37:28,144 --> 00:37:29,511
>> As strong as a tornado,

1028
00:37:29,579 --> 00:37:31,480
the wind blast uprooted trees a

1029
00:37:31,514 --> 00:37:33,482
half-mile away from the impact

1030
00:37:33,516 --> 00:37:34,850
zone.

1031
00:37:34,884 --> 00:37:36,685
>> We can have about 3,000

1032
00:37:36,786 --> 00:37:39,254
people go up and down that trail

1033
00:37:39,322 --> 00:37:42,224
in one day, and so we did not

1034
00:37:42,325 --> 00:37:43,759
know how many people were

1035
00:37:43,793 --> 00:37:45,961
trapped under the trees. And,

1036
00:37:46,062 --> 00:37:48,063
tragically, a young man was

1037
00:37:48,164 --> 00:37:50,466
pinned by a tree and was killed,

1038
00:37:50,533 --> 00:37:52,234
and a young woman was trapped

1039
00:37:52,268 --> 00:37:56,872
under a tree and is paralyzed.

1040
00:37:56,906 --> 00:37:59,441
>> A deadly, mysterious force is

1041
00:37:59,509 --> 00:38:01,910
continually at work in Yosemite,

1042
00:38:01,978 --> 00:38:03,345
causing the surface layers of

1043
00:38:03,446 --> 00:38:05,247
the ultra-tough Yosemite granite

1044
00:38:05,281 --> 00:38:08,550
to peel away in huge chunks.

1045
00:38:08,618 --> 00:38:10,452
One large rock fall occurs every

1046
00:38:10,553 --> 00:38:12,888
week in the park, and yet up to

1047
00:38:12,989 --> 00:38:15,257
4 million people visit Yosemite

1048
00:38:15,358 --> 00:38:17,159
each year, getting perilously

1049
00:38:17,260 --> 00:38:18,594
close to these potentially

1050
00:38:18,628 --> 00:38:21,797
unstable cliffs.

1051
00:38:21,865 --> 00:38:23,999
To discover what's causing

1052
00:38:24,067 --> 00:38:25,734
Yosemite's incredibly tough

1053
00:38:25,802 --> 00:38:27,436
granite to fall down,

1054
00:38:27,537 --> 00:38:28,904
researchers have dotted

1055
00:38:28,972 --> 00:38:30,372
vibration sensors and

1056
00:38:30,440 --> 00:38:32,007
solar-powered seismic stations

1057
00:38:32,075 --> 00:38:33,942
all over Yosemite's cliffs,

1058
00:38:33,977 --> 00:38:35,811
enabling them to listen to the

1059
00:38:35,912 --> 00:38:37,346
rocks.

1060
00:38:37,413 --> 00:38:39,181
>> This computer allows me to

1061
00:38:39,249 --> 00:38:40,549
see what's going on all the

1062
00:38:40,617 --> 00:38:41,984
time.

1063
00:38:41,985 --> 00:38:44,419
For example, if I throw this

1064
00:38:44,454 --> 00:38:50,425
rock at the cliff over there...

1065
00:38:50,426 --> 00:38:52,427
I just created a mini-rock fall,

1066
00:38:52,462 --> 00:38:54,363
and take a look. And these

1067
00:38:54,430 --> 00:38:55,531
spikes are the rock hitting the

1068
00:38:55,632 --> 00:38:56,999
cliff and then tumbling down.

1069
00:38:57,066 --> 00:38:58,267
This is a mini rock fall that

1070
00:38:58,334 --> 00:38:59,635
happened right here.

1071
00:38:59,702 --> 00:39:00,636
So the station will pick up

1072
00:39:00,703 --> 00:39:01,603
rock falls that happen that are

1073
00:39:01,638 --> 00:39:02,971
small right here, but it'll pick

1074
00:39:03,072 --> 00:39:05,774
up larger ones in other places.

1075
00:39:05,808 --> 00:39:07,442
>> This seismic listening device

1076
00:39:07,544 --> 00:39:09,311
has pinpointed a recent rock

1077
00:39:09,345 --> 00:39:11,780
fall behind Half Dome.

1078
00:39:11,814 --> 00:39:13,982
It's a chance for Valerie Zimmer

1079
00:39:14,083 --> 00:39:16,151
to investigate why Yosemite's

1080
00:39:16,185 --> 00:39:18,887
rocks are falling down, and all

1081
00:39:18,988 --> 00:39:20,789
the evidence indicates another

1082
00:39:20,857 --> 00:39:26,528
cataclysmic event has occurred.

1083
00:39:26,596 --> 00:39:30,699
>> Oh, look at this.

1084
00:39:30,767 --> 00:39:31,900
All these trees have been

1085
00:39:31,968 --> 00:39:32,801
knocked over like they're

1086
00:39:32,869 --> 00:39:33,969
toothpicks.

1087
00:39:34,037 --> 00:39:35,871
These rocks range from the size

1088
00:39:35,905 --> 00:39:38,407
of a house to just dust.

1089
00:39:38,441 --> 00:39:40,309
>> Analysis of the seismic data

1090
00:39:40,410 --> 00:39:42,144
shows this was a massive rock

1091
00:39:42,211 --> 00:39:44,012
fall, one of the biggest in the

1092
00:39:44,047 --> 00:39:46,582
last 20 years. It shook the

1093
00:39:46,649 --> 00:39:48,116
ground so hard, it was the

1094
00:39:48,184 --> 00:39:50,319
equivalent of a magnitude 2.4

1095
00:39:50,386 --> 00:39:52,220
earthquake.

1096
00:39:52,322 --> 00:39:53,855
>> If you look up on that

1097
00:39:53,923 --> 00:39:55,090
mountain, the amount of rocks

1098
00:39:55,124 --> 00:39:56,291
that came down, you know, you

1099
00:39:56,326 --> 00:39:57,326
look up high, it doesn't look

1100
00:39:57,393 --> 00:39:58,727
like a big area, but it's

1101
00:39:58,761 --> 00:40:00,862
deceivingly large. It's probably

1102
00:40:00,930 --> 00:40:03,298
the size of maybe 40 houses

1103
00:40:03,399 --> 00:40:05,100
all together.

1104
00:40:05,134 --> 00:40:07,235
>> Strangely, immediately above

1105
00:40:07,303 --> 00:40:09,037
the scarred rock face, a new

1106
00:40:09,138 --> 00:40:11,673
dome is forming.

1107
00:40:15,845 --> 00:40:18,213
Mysterious domes are forming all

1108
00:40:18,314 --> 00:40:20,115
over the valley, the most

1109
00:40:20,216 --> 00:40:22,584
famous--Half Dome.

1110
00:40:22,652 --> 00:40:24,453
Glaciers cleaved its vertical

1111
00:40:24,554 --> 00:40:26,855
face, but its domed top has been

1112
00:40:26,956 --> 00:40:29,291
shrouded in mystery.

1113
00:40:29,392 --> 00:40:31,193
A strange underlying force is

1114
00:40:31,227 --> 00:40:32,928
sculpting these peaks into

1115
00:40:33,029 --> 00:40:35,197
domes, causing the rocks to

1116
00:40:35,298 --> 00:40:37,899
tumble down.

1117
00:40:41,471 --> 00:40:43,438
North of Yosemite, on the dome

1118
00:40:43,506 --> 00:40:45,340
at Olmstead Point, it's possible

1119
00:40:45,375 --> 00:40:46,608
to get close enough to

1120
00:40:46,643 --> 00:40:48,243
investigate why the surface

1121
00:40:48,277 --> 00:40:49,511
layers of granite are

1122
00:40:49,545 --> 00:40:50,979
shattering.

1123
00:40:51,080 --> 00:40:52,280
>> These domes are all over the

1124
00:40:52,348 --> 00:40:54,282
place. You see these layers

1125
00:40:54,350 --> 00:40:56,351
running parallel to the surface.

1126
00:40:56,452 --> 00:40:57,719
They're almost like the layers

1127
00:40:57,820 --> 00:41:00,155
on an onion, and the layers are

1128
00:41:00,189 --> 00:41:01,456
starting to peel off. In fact,

1129
00:41:01,524 --> 00:41:02,457
look right here. This one is

1130
00:41:02,525 --> 00:41:03,959
coming apart.

1131
00:41:03,993 --> 00:41:05,727
>> The outer surface of the rock

1132
00:41:05,795 --> 00:41:07,629
has fractured into layers,

1133
00:41:07,730 --> 00:41:09,064
running over the summit and down

1134
00:41:09,098 --> 00:41:13,602
the sides of the dome.

1135
00:41:13,636 --> 00:41:15,537
>> These are weaknesses in the

1136
00:41:15,605 --> 00:41:18,540
rock. It's obvious that there

1137
00:41:18,608 --> 00:41:20,809
must be some sort of force

1138
00:41:20,877 --> 00:41:22,411
that's causing the rock to break

1139
00:41:22,445 --> 00:41:24,913
in this way and peel apart

1140
00:41:24,981 --> 00:41:26,815
like an onion.

1141
00:41:26,883 --> 00:41:28,450
>> The only force capable of

1142
00:41:28,518 --> 00:41:29,985
fracturing the ultra-tough

1143
00:41:30,053 --> 00:41:31,820
Yosemite granite like this

1144
00:41:31,888 --> 00:41:33,522
originates deep within the

1145
00:41:33,623 --> 00:41:36,792
Earth.

1146
00:41:36,893 --> 00:41:38,994
100 million years ago, the

1147
00:41:39,062 --> 00:41:40,629
Yosemite granite is beginning

1148
00:41:40,697 --> 00:41:43,331
to form. Submerged beneath two

1149
00:41:43,366 --> 00:41:45,634
miles of volcanic rock, it's

1150
00:41:45,702 --> 00:41:47,703
squashed and squeezed from every

1151
00:41:47,770 --> 00:41:49,171
direction.

1152
00:41:49,272 --> 00:41:50,605
Over the next 40 million years,

1153
00:41:50,707 --> 00:41:53,709
the volcanic roof erodes away.

1154
00:41:53,776 --> 00:41:55,544
The immense downward pressure is

1155
00:41:55,611 --> 00:41:57,813
removed, leaving these titanic

1156
00:41:57,880 --> 00:41:59,948
forces out of balance.

1157
00:41:59,982 --> 00:42:01,349
The surface of the exposed

1158
00:42:01,417 --> 00:42:02,984
Yosemite granite is now an

1159
00:42:03,052 --> 00:42:04,419
avenue through which this

1160
00:42:04,520 --> 00:42:05,887
pent-up pressure can be

1161
00:42:05,988 --> 00:42:08,423
released.

1162
00:42:11,894 --> 00:42:13,061
>> The granite is still being

1163
00:42:13,162 --> 00:42:14,162
squeezed from the sides and from

1164
00:42:14,230 --> 00:42:15,764
the bottom, but at the surface

1165
00:42:15,798 --> 00:42:17,065
it's free to move.

1166
00:42:17,166 --> 00:42:18,433
What happens is these layers

1167
00:42:18,501 --> 00:42:20,402
start to open up parallel to

1168
00:42:20,436 --> 00:42:21,503
the surface.

1169
00:42:21,537 --> 00:42:22,671
>> The release of this ancient

1170
00:42:22,705 --> 00:42:24,172
pressure causes the surface of

1171
00:42:24,240 --> 00:42:25,807
the granite to fracture into

1172
00:42:25,875 --> 00:42:27,976
onion layers, which then peel

1173
00:42:28,077 --> 00:42:29,311
away.

1174
00:42:29,345 --> 00:42:30,445
>> And so, when the tops of

1175
00:42:30,513 --> 00:42:31,780
those mountains fall off, you're

1176
00:42:31,881 --> 00:42:32,981
left with rounded domes.

1177
00:42:33,082 --> 00:42:34,983
>> But it's not just the granite

1178
00:42:35,051 --> 00:42:36,518
peaks that are affected.

1179
00:42:36,619 --> 00:42:39,321
It's the cliffs, too.

1180
00:42:39,355 --> 00:42:40,622
>> These layers are also formed

1181
00:42:40,690 --> 00:42:41,990
if the ground surface is

1182
00:42:42,058 --> 00:42:43,792
vertical like a cliff, creating

1183
00:42:43,860 --> 00:42:45,894
vertical fractures alongside the

1184
00:42:45,962 --> 00:42:47,696
cliff. These vertical fractures

1185
00:42:47,764 --> 00:42:49,397
allow the rock to then slide out

1186
00:42:49,432 --> 00:42:52,167
and create rock falls, and this

1187
00:42:52,235 --> 00:42:53,502
is one of the major contributing

1188
00:42:53,536 --> 00:42:54,503
factors to rock falls

1189
00:42:54,604 --> 00:42:56,037
in Yosemite.

1190
00:42:56,072 --> 00:42:57,506
>> Yosemite's catastrophic rock

1191
00:42:57,607 --> 00:42:59,241
falls are the legacy of its

1192
00:42:59,308 --> 00:43:00,976
prehistoric birth beneath the

1193
00:43:01,043 --> 00:43:03,879
Earth, 100 million years ago.

1194
00:43:03,980 --> 00:43:06,214
The gradual release of this

1195
00:43:06,249 --> 00:43:07,949
ancient, pent-up pressure has

1196
00:43:07,984 --> 00:43:10,051
created an untamed and dynamic

1197
00:43:10,119 --> 00:43:12,220
landscape.

1198
00:43:12,255 --> 00:43:13,488
>> Rock fall is a natural

1199
00:43:13,523 --> 00:43:15,323
process and is part of the

1200
00:43:15,424 --> 00:43:17,325
ongoing evolution of Yosemite

1201
00:43:17,393 --> 00:43:19,427
National Park. I always get

1202
00:43:19,495 --> 00:43:21,396
a little bit tickled when people

1203
00:43:21,430 --> 00:43:23,665
ask me questions like, "what are

1204
00:43:23,699 --> 00:43:24,499
You going to do to prevent

1205
00:43:24,600 --> 00:43:26,067
future rock falls?"

1206
00:43:26,135 --> 00:43:27,402
It's a constant reminder that

1207
00:43:27,470 --> 00:43:29,471
this is a wild place and that

1208
00:43:29,539 --> 00:43:31,273
there's nothing we can do or

1209
00:43:31,307 --> 00:43:34,209
should do to tame it in any way,

1210
00:43:34,277 --> 00:43:35,677
shape, or form. But it's

1211
00:43:35,745 --> 00:43:37,445
something that, after I'm long

1212
00:43:37,480 --> 00:43:40,348
gone, will continue to happen.

1213
00:43:40,383 --> 00:43:43,018
>> For the last 150 years,

1214
00:43:43,119 --> 00:43:44,486
scientists have been figuring

1215
00:43:44,554 --> 00:43:46,555
out how this magnificent valley

1216
00:43:46,622 --> 00:43:47,923
formed.

1217
00:43:47,990 --> 00:43:49,658
They found...

1218
00:43:49,725 --> 00:43:51,726
volcanic rocks--proof that the

1219
00:43:51,761 --> 00:43:53,361
molten granite cooled deep

1220
00:43:53,396 --> 00:43:55,363
beneath the earth;

1221
00:43:55,398 --> 00:43:57,666
karge crystals--evidence that

1222
00:43:57,733 --> 00:43:59,534
Yosemite granite cooled slowly,

1223
00:43:59,569 --> 00:44:02,838
creating tough, faultless rock;

1224
00:44:02,939 --> 00:44:05,207
Rapids downstream show that

1225
00:44:05,274 --> 00:44:06,942
the Merced River cut a deep,

1226
00:44:07,009 --> 00:44:09,477
V-shaped canyon;

1227
00:44:09,545 --> 00:44:11,746
And rocks carried by a glacier--

1228
00:44:11,814 --> 00:44:13,582
conclusive evidence that ice

1229
00:44:13,649 --> 00:44:15,750
carved Yosemite's steep cliffs

1230
00:44:15,818 --> 00:44:19,621
and flattened its valley floor.

1231
00:44:22,725 --> 00:44:25,727
Yosemite, a valley of giants,

1232
00:44:25,828 --> 00:44:28,363
is a geological masterpiece.

1233
00:44:28,364 --> 00:44:30,198
The unique strength of its

1234
00:44:30,266 --> 00:44:32,000
near-perfect granite has created

1235
00:44:32,034 --> 00:44:33,735
some of the most imposing and

1236
00:44:33,803 --> 00:44:35,704
iconic landscapes on planet

1237
00:44:35,738 --> 00:44:38,573
Earth, one where the deep earth

1238
00:44:38,641 --> 00:44:40,208
forces that created it are

1239
00:44:40,276 --> 00:44:42,377
continuing to shape its future,

1240
00:44:42,478 --> 00:44:45,814
Living proof that the earth is

1241
00:44:45,848 --> 00:44:48,150
never at rest.

1242
00:44:48,184 --> 00:44:53,284
-- Sync, corrected by <font color=#00FF00>elderman</font> --
-- for addic7ed.com ---