Photo Credit: Frank Kovalchek

Exploring the Kenai Mountains-Turnagain Arm National Heritage Area: Summit Lake Effects of Glaciation

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SUMMIT LAKE

Landforms Resulting from Persistent Post-glacial Ice

Location:    Approximately Mile 45: Summit Lake Pull-off

Pull off midway on Upper Summit Lake (south of lodge)

Short Description:          Benches above lake provide clues to a different type of glacial history.

Required Equipment:       None

Suggested Equipment:    None

Safety Consideration: Pull-off is adjacent to busy highway

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Inquiry Prompts:  What’s Going On Here?

Prompt students to consider the slope immediately rising up from the shore of the lake. Is there anything that is different about this slope? There are two visual clues that students need to focus upon:

  • Slight bench above Summit Lake (that disappears some ways after lake so therefore can be assumed to be associated with lake.
  • Faint alluvial fans coming down to bench.

At first glance it doesn’t seem too much of an issue; just a bench above the lake. But alas, trying to explain it might be a bit confounding. Glaciers have certainly had a profound effect in this valley (as evidenced by the classic glacier U-shape and the striations on the sides of mountains). Could this bench just be your run-of-the-mill glacial moraine? No, something else is happening here.

The Rest of the Story:

Indeed the bench and related alluvial fans are glacier-related. It was the end of the Naptown glaciation (some 12,000 years ago) that the glacier that once occupied this valley melted. The last remnants of that glacier was a shadow of its former self (the area of Summit Lake). The melting slowed and movement ceased— the ice persisted, Prior to melting entirely, rock loosen from above fell and formed a colluvial fan at the margins of this shrinking form that once was a proud and mighty glacier. The faint colluvial fans provide further evidence of this geologic phenomenon.

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