GEOG 3251: MOUNTAIN GEOGRAPHY
SUMMER 2007 TERM A
Field trip: Adina Racoviteanu and Andrés Holz
FIELD TRIP TO ISABELLE LAKE, INDIAN PEAKS
June 29, 2007
MEET AT THE REC CENTER TURN AROUND AT 8 AM. WE WILL DEPART
PROMPTLY.
General Objectives: This field trip investigates the altitudinal variation of vegetation
and glacial geomorphology found in the Indian Peaks section of the Colorado Front
Range. As we walk along the trail, we will integrate all the concepts studied in class so
far, from mountain orogeny to mountain climate, and glacier landforms to alpine
vegetation patterns. After this fieldtrip
you should be able to:
o
o
o
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o
o
o
aretes
U-shaped valley
cirque
tarn
moraines
identify species present in the subalpine and alpine zone in Colorado
Describe how the vegetation relates to location (elevation) and climate.
explain how past climates are reconstructed from tree rings
Key Geographical Concepts addressed by this fieldtrip:
o
o
o
identify the major alpine
glacial landforms in
pictures or real life;
recognize alpine glacial
landforms on a
topographic map;
Describe how the
following alpine glacial
and periglacial landforms
are created:
landform identification
species identification
topographic map reading skills
Gear Requirements:
o
o
o
o
o
o
o
hiking boots (the trail is muddy in places and there is still some snow on
the ground)
raingear
sunblock
sunglasses
hat, gloves
warm layers (fleece)
notebook and pen to take notes
Activities:
o
o
locate and identify alpine glacial landforms on topographic maps and in
pictures
hands-on: drilling a tree core demo and practice- led by Andrés Holz,
Biogeography Lab, University of Colorado.
Time Requirements:
o
Approximately 5 hours total; It takes 45 minutes-1 hrs to drive one way.
We will be hiking for about 1 hr and spend time identifying landforms and
drilling tree cores for 45 min- 1 hrs. Estimated return time: 1 pm.
Access and Trail Description:
Lake Isabelle is reached on one of the more beautiful trails in the Front Range. It is a
steady climb from Long Lake but not particularly steep until you are very near Lake
Isabelle. The lake lies near timberline in a dramatic valley, offering views of high peaks
such as Navajo and Apache Peaks. The trail ends finally beside Isabelle Glacier in a very
steep-walled cirque basin framed by Shoshone, Apache and Navajo Peaks – due to time
constraints we will not be able to go to the glacier, but we can still observe the glacier
landforms from the lake.
Distance: 2.0 miles one-way
Lake elevation: 10,868 feet
Trailhead elevation: 10,480 feet
Net elevation gain: 388 feet
Long Lake Trailhead
Ending
point
Starting
point
An Introduction to the Indian Peaks.
Text adapted from Mike Ritter ( mritter@uwsp.edu )
GEOLOGY
Geologically speaking, the Front Range is bordered on the east by a series of narrow
sedimentary cuestas and hogbacks, locally known as the FlatIrons and tectonic
depressions to the west and south. The range itself is composed of a core of Precambrian
intrusives, themselves intruded by Tertiary plutons.
Looking west towards the Flat
Irons from Boulder, Colorado
(Photo credit Michael Ritter,
1984)
The Front Range rises from the high
plains near Denver, Colorado at
approximately 5,280 feet to an
elevation of over 13,500 feet. The
crestline of the range forms the
Continental Divide. The range
appears to slope gently to the east as
a series of broad benches, described by some as remnants of former erosion surfaces. The
topography of the Indian Peaks section has been carved by a combination of fluvial and
glacial activity. The surface has been deeply dissected, first by the cutting of river valleys
which were later modified by Pleistocene glaciation. Many areas were later affected by
Holocene glaciation as well.
Actually, glacial erosion has not advanced very far, so that the higher elevations represent
a balance between the steep glacial topography and broadly flowing uplands. Elevations
drop precipitously on the west of the continental divide.
Oblique aerial photograph taken from east of
Green Lakes Valley (left of center) and Niwot
Ridge (the broadening ridge running from center
to lower right of image) in July. (Photo used with
permission. http://culter.colorado.edu:1030/)
CLIMATE
The strong westerly winds exert an important
control over the character of the Front Range
environment. Interacting with topography, deposition and accumulation of snow occurs
on eastern, lee side situations yielding a predominance of cirque forms with easterly
orientations. A similar control is placed on the distribution of perennial and late-lying
snow banks affecting the distribution of plant communities.
VEGETATION
Four distinct ecosystems are found above the short grass prairie that lies at the base of the
range:
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the colline belt where Ponderosa Pine and Douglas fir dominate;
the montane forest which is subdivided into the lower montane with a
predominance of lodgepole pine and intermixed aspen and the upper montane of
Engelmann spruce,
subalpine fir and limber pine;
treeless alpine tundra.
Nival
Alpine
treeline
Subalpine
Montane
SNOW AND ICE
Isabelle Glacier
Isabelle Glacier is one of the smaller glaciers in the Front Range. Studies have shown that
this glacier seems to be in a state of equilibrium with its environment, neither expanding
Nor contracting much over time (Outcault and McPhail, 1965). Movement has taken
place, as crevasses are apparent on the surface of the glacier. Crevasses are cracks in the
ice created by differential movement or, expansion and contraction taking place within
the ice.
Figure 6.2 Crevasse on the surface of
Isabelle Glacier (Photo credit: N. C.
Heywood)
Figure 6.1 Isabelle Glacier from the air
CIRQUE:
a semicircular or amphitheatershaped bedrock feature created
as glaciers scour back into the
mountain. Under the weight of
accumulated snow and ice at the
head of a river valley, a mountain
glacier plucks away at the head of
the valley over several hundreds of
years sculpting the valley head into
a natural amphitheater. This is the
"headwaters“ of a glacier.
ARETE:
steep-sided, sharp-edged
bedrock ridge formed by
two glaciers eroding away
on opposite sides of the ridge
HORN:
a pyramid-shaped mountain peak created by several
glaciers eroding away at different sides
of the same mountain.
TARN:
a glacial lake produced by scouring. These
are often found in cirques.
PATTERNOSTER (STAIRCASE) LAKES
Paternoster, or staircase lakes, form by
carving out a valley bed of varying
resistance of rock to glacial erosion, or by
the damming effect of glacial deposits. In
the first case, as glaciers move down
valley from the zone of accumulation, they
erode the bed beneath the ice. Often, the
bed or valley is composed of different rock
types of varying resistance to erosion.
When the glacier encounters weaker rock,
it can erode more (deeper) than when it
encounters strong, more resistant rock. As a result, depressions are formed in the weak
rock, in which water accumulates after the glacier recedes upslope. The lakes are "strung
together" by a stream that runs between them.
GLACIER LANDSCAPE FEATURES OVERVIEW
Life in the snowpack: WATERMELON SNOW
No. it’s not a murder scene!