NH - Talus Deposits in Tuckerman’s Ravine EarthCache
Hidden : 7/20/2013
Difficulty:
2.5 out of 5
Terrain:
4.5 out of 5

Size: Size: other (other)

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Geocache Description:

Tuckerman Ravine is a cirque located on Mt. Washington in the White Mountains of northern New Hampshire. Mt. Washington is the highest peak in the northeastern United States. At 6,288 feet (1,916 meters), this mountain is notorious for rapidly changing weather and serious wind gusts (231 miles/hour - at one time the highest gust ever recorded). Tuckerman Ravine was formed as glaciers eroded rock during the Pleistocene epoch about two million years ago.


Talus
Talus is the name for rock piles formed at the edge of cliffs. It is a collection of broken rock fragments at the base of mountain cliffs, volcanoes or valley shoulders that has accumulated through periodic rockfall from adjacent cliff faces. Landforms associated with these materials are often called talus deposits. Talus deposits typically have an upwards facing form, while the maximum inclination corresponds to the angle of repose of the average debris size.

Formation of talus deposits results from physical and chemical weathering and erosion acting on a rock face. The processes that degrade a rock slope depend largely on the regional climate (temperature, rainfall, wind, etc.). Talus is commonly attributed to the formation of ice within mountain rock slopes. During the day, water can flow in joints and discontinuities in the rock wall. If the temperature drops sufficiently, for example with the onset of evening, this water may freeze. Water expands by 9% when it freezes so it can generate large forces that either create new cracks or wedge blocks into an unstable position. Freeze-and-thaw talus production is thought to be most common during the spring and fall, when the daily temperatures fluctuate around the freezing point of water, and snow melt produces ample free water.

There are four talus piles in this ravine, which formed as rocks broke from the main formations and toppled down the mountainside.


"Talus Site 1 is a linear feature that heads in the downvalley end of the upper cirque and spills over the scarp of the Little Headwall into the lower cirque. Most of this deposit lies at the foot of a buttress known as Lion Head. In the course of earlier, primarily reconnaissance-level research, Site 1 was thought to have derived from no less than three different geomorphic processes. Talus Sites 2 and 3 are located on the north wall and Site 4 is situated at the downvalley edge of the south wall of the upper cirque. Site 2 has a conical shape that is typical of talus deposits and Sites 3 and 4 are irregularly shaped due to the morphology of the cirque walls." From the article "Talus fabric in Tuckerman Ravine, New Hampshire: Evidence for a tongue-shaped rock glacier" by David Thompson.

Activity
1. At the coordinates for Ground Zero turn around if you are coming up Tuckerman's ravine and see the deposits to the north (#2 shown in the picture above) and south (#4). Note that they piled up in a specific pattern. Send me a message with the average dimensions of several of these rocks, as well as the patterns for each formating and your thoughts as to what caused them to form here in this way.
2. Identify your altitude at the spot of this Earthcache - estimate the altitude of Talus #2 and #4 at the peak and the bottom of the cliff and determine (best guess) the drop-off in feet
3. Send me an e-mail with the answers to #1 and #2
4. Optional: Take a photo of yourself with the Talus Site behind you

Additional Hints (No hints available.)



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