Tuesday, September 29, 2009

Back in the Mountains- rock glaciers

My kids already know that I enjoy the finer things in life. The sun setting with palm trees in the foreground, fresh squeezed orange juice and rock glaciers. The San Juan mountains seem to have more than a few rock glaciers to observe and very few palm trees. These two examples are near Molas Pass on Highway 550. Hike south on the Colorado Trail and you will pass both within the first fifteen miles.

The basic ingredients to rock glaciers are pretty simple.
1. Lots of rocks! In both cases, the raw materials, talus, are made from the weathering of volcanic tuff. This volcanic rock is brittle and weathers easily into smaller chunks of rock. Mountains are great places for freeze-thaw weathering as almost every day of the year sees temperatures above and below 0 degrees C.

2. Frozen water. Within the pore space of these talus fields we find ice. Water has filtered between the rocks of the rock glacier and has frozen into place. Even though temperatures will rise above 0 C often, the insulating property of the rocks coupled with the lack of direct sunlight beneath the rocks keep the water frozen.

3. A slope. After even a small time hiking these mountains it is easy to see there is very little level ground. A slope is not hard to find.

Plenty of rock available. An obvious slope and we will assume some ice present under the surface layer of rock.
Notice the ribbing of rock. An ice glacier will exhibit similar crevasse fields from the movement of the mass.