Geoscience Reference
In-Depth Information
Te ton Mountains
WEST
EAST
Grand Teton
13,770 ft.
Jackson Hole
Blacktail Butte
Mesozoic
Jackson
Quaternary
Precambrian
Paleozoic
sea level
0
10 km
0
10 mi
Fig. 15.4. Geologic structure of the teton Range and Jackson
Hole. continuing displacement along the teton fault has
created a mountain range without foothills. the Quaternary
deposits are mostly alluvium, often referred to as glacial out-
wash plains, deposited as the glaciers melted. Adapted from
Love et al. (2003).
about 80,000 years ago and reached its maximum extent
of what is now YnP and was about 4,000 feet thick above
the Yellowstone Lake basin. ice buried and subsequently
carved many mountains in the area, including Mount
Washburn and Mount Sheridan. the ice also dammed
the Yellowstone River, causing Yellowstone Lake to
expand and cover the area that today is Hayden Valley.
Fine-textured sediments deposited during that time in
the bottom of the lake now support extensive meadows.
Several thousand feet of ice also covered the north-
ciers flowing down the canyons of the tetons created
terminal moraines at the foot of the mountains, form-
ing lakes known today by the names of early explor-
ers—Jackson, Bradley, Jenny, Leigh, Phelps, and taggart.
Glaciers also shaped the jagged peaks and U-shaped val-
leys of the teton, Beartooth, and Wind River Mountains
(see fig. 2.6).
the glaciers began to shrink as the climate warmed,
about 20,000 years ago, leading to the gradual elimina-
tion of the vast Yellowstone ice field. evidence suggests
that a glacier persisted in Jackson Hole until as recently
as 9,000 years ago. it would have been witnessed by
some of the earliest native Americans as they entered
the valley. With rapid thawing of huge masses of ice,
rivers became swollen with water and sediment. Great
floods occurred as moraines and ice dams collapsed,
depositing large outwash plains (such as Antelope Flats)
and scouring stream bottoms. the extensive terraces
along the Snake River were formed during this time (see
fig. 15.3). Further evidence of the glaciers is apparent
in pothole topography. Also known as kettles, these
potholes were created by the melting of huge blocks
of ice buried in the moraines. Water-filled depressions
remained after the ice disappeared (see chapter 5).
Based on fossil pollen records from lake sediments,
paleoecologist cathy Whitlock and colleagues deter-
mined that tundra was prevalent in much of the GYe
engelmann spruce began to dot the tundra where a
more fertile substrate had developed from andesitic
rocks. Whitebark pine and subalpine fir joined the
spruce about 11,000 to 9,500 years ago, but the less fer-
tile rhyolitic soils of the Yellowstone Plateau remained
unforested during this period. the climate gradually
became warmer, though it was still cooler and more
humid than it is today. continued warming led to the
expansion of lodgepole pine throughout the region.
Whitlock's data indicate that limber pine was present at
low elevations and that Douglas-fir expanded to higher
elevations about 9,500 to 4,500 years ago. Subsequently,
the climate became cooler and wetter at high eleva-
tions, enabling spruce and fir to become more common,
along with lodgepole pine, as they are today. Douglas-fir
now grows at lower elevations.
today, the GYe spreads over fourteen mountain
ranges and is a major source of water for three major
river systems—the Green flowing into the colorado, the
Snake into the columbia, and the Yellowstone into the
forested, with lodgepole pine, engelmann spruce and
subalpine fir, and aspen dominating an estimated 20,
12, and 3 percent of the land, respectively. About 10
Search WWH ::
Custom Search