Geog 3251: Mountain Geography

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  identify the major alpine glacial landforms in pictures or real life;

o  recognize alpine glacial landforms on a topographic map;

o  Describe how the following alpine glacial and periglacial landforms are created:

§  aretes

§  U-shaped valley

§  cirque

§  tarn

§  moraines

o  identify species present in the subalpine and alpine zone in Colorado

o  Describe how the vegetation relates to location (elevation) and climate.

o  explain how past climates are reconstructed from tree rings

Key Geographical Concepts addressed by this fieldtrip:

o  landform identification

o  species identification

o  topographic map reading skills

Gear Requirements:

o  hiking boots (the trail is muddy in places and there is still some snow on the ground)

o  raingear

o  sunblock

o  sunglasses

o  hat, gloves

o  warm layers (fleece)

o  notebook and pen to take notes

Activities:

o  locate and identify alpine glacial landforms on topographic maps and in pictures

o  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

An Introduction to the Indian Peaks.

Text adapted from Mike Ritter ( )

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:

·  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.

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.

CIRQUE:

a semicircular or amphitheater- shaped 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!