Mt. Washington is a nearly extinct volcano in the Cascade Range of western Oregon. This peak is the remaining central plug of a highly eroded composite volcano with an estimated age of no more than a few 100,000 years. Thick basalt flows make up the base of the mountain while mixed flows and ash comprise the upper portions of the debris pile surrounding the main peak. During the late Pleistocene the flanks of the summit cone were excavated by valley glaciers which extended more than 12 kilometers east and west. Glaciers and the general instability of volcanoes have together eroded it to the state we see today.
Glaciated mountain regions exhibit a number of distinct features created by erosion such as cirques, horns, arêtes, U-shaped valleys, hanging valleys and truncated spurs.
| A cirque (from a French word for "arena"), corrie (from Scottish Gaelic coire meaning a pot or cauldron) or cwm (Welsh for "valley") is an amphitheatre-like valley head, formed at the head of a valley glacier by erosion. The concave amphitheatre shape is open on the downhill side corresponding to the flatter area of the stage, while the cupped seating section is generally steep cliff-like slopes down which ice and glaciated debris combine and converge from the three or more higher sides. The floor of the cirque ends up bowl shaped as it is the complex convergence zone of combining ice flows from multiple directions. |
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| Horns are pyramidal peaks which form when several cirques erode a mountain from three or more sides. Perhaps the most famous horn is the Matterhorn in Switzerland. |
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| An arête is a thin, almost knife-like, ridge of rock which is typically formed when two glaciers erode parallel U-shaped valleys. The arête is a thin ridge of rock that is left separating the two valleys. The edge is then sharpened by freeze-thaw weathering, and the slope on either side of the arête steepened through mass wasting events and the erosion of exposed, unstable rock. The word "arête" is actually French for edge or ridge. |
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| U-shaped valleys are valleys carved by glaciers becoming visible upon the recession of the glacier that forms it. When the ice recedes or thaws, the valley remains, often littered with small boulders that were transported within the ice. Floor gradient does not affect the valley's shape, it is the glacier's size that does. Continuously flowing glaciers – especially in the ice age – and large-sized glaciers carve wide, deep incised valleys. |
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| A hanging valley is a tributary valley with the floor at a higher relief than the main channel into which it flows. They are most commonly associated with U-shaped valleys when a tributary glacier flows into a glacier of larger volume. The main glacier erodes a deep U-shaped valley with nearly vertical sides while the tributary glacier, with a smaller volume of ice, makes a shallower U-shaped valley. Since the surfaces of the glaciers were originally at the same elevation, the shallower valley appears to be ‘hanging’ above the main valley. Bridal Veil Falls in Yosemite National Park is an example of a hanging valley. |
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| Truncated spurs are blunt-ended rock ridges which descend from the steep sides of a U-shaped valley and are often separated by hanging valleys. Valley glaciers tend to follow a straighter course than river channels and erode the interlocking spurs of the upper course valley, cutting through the projecting ridges. |
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To log this cache email me the answers to the following questions;
1) Observe Mt. Washington and the surrounding landscape and identify two features created by glaciation. All answers are subjective and there is no correct answer, simply state what you observed.
2) Two animals are pictured on the sign “Survival in a forest of trees”. What are they?
Glaciers are also responsible for many other formations and phenomena not directly related to the alpine environment. For more information please see the following references.
USGS
Wikipedia
Physical Geography
Not required for a log submission but highly encouraged, include a photo of yourself in front of Mt. Washington in your log.