Williwaw Valley Photo

This photo was taken in October 1998, above Williwaw Valley in the Chugach mountains just east of Anchorage.

Cirques
A glacial cirque is a unique geographic feature formed at the head of alpine glaciers.  Glaciers often pluck out the bedrock that lies underneath the head of the glacier and carries the material down into the valleys below.  Holes of surprising depth, known as cirques, can be created in these locations.  Often these cirques fill with lakes, called tarns.  While the glaciers retreated from the Anchorage area almost 10,000 years ago, they often remained at high elevations such as this until only several hundred years ago.

Chugach Mountains
The Chugach Mountains are made of metamorphosed sediments that were deposited in the now extinct Border Ranges Trench, an ancient subduction zone.  The sediments had been washed off of a microcontinent known as Wrangellia.  About 50 million years ago, Wrangellia slammed into southern Alaska.  The Border Ranges Trench closed up in this collision and the material within it was uplifted as the Chugach Mountains, which form the bulk of southern Alaska as we know it today.  Wrangellia itself consisted of areas such as the Talkeetna Mountains, some of the Alaska Range and the bedrock underlying the Wrangell volcanoes.

Clouds
The fog in the mountains is created as warmer air rises above cooler air.  In this case warm air (or relatively warm, it's all pretty cool in October) from the Anchorage area is rises up the mountain slopes to higher elevations.  As the air cools, it reaches it's dew point and some of it's moisture content is released, causing clouds at higher altitudes.  In this case, the dew point is at a lower altitude than the highest mountain peaks, creating a beautiful and eerie landscape in the craggy peaks of the Chugach.

Tundra
The vegetation seen in the photo is alpine tundra.  While tundra is normally associated with the high arctic regions. It is also common at higher elevations in the subarctic and even more temperate regions.  The tiny, hardy plants are specially adapted to withstand cold weather for almost the entire year.  Trees need at least one month with an average temperature above 50 degrees F or so in order to inhabit an area.  This is an unusual photo in that the tundra is not already covered by snow.  It is very rare that there is no snow at this elevation by mid-October.

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