Wednesday, August 25, 2010

Dying Glaciers and Fossilized Black Smokers


This post is about the geology of the Alpine Lakes wilderness, where I spent the last five days hiking from lake to lake, and observing the landscape.

Let's start with the glaciers. The most recent glaciation came to an end about 10,000 years ago. Of course, there are still a few remnants of this last ice age, but, as you will see, these are shrinking.

Glaciers have certainly left their
mark on the landscape, carving out innumerable lakes of picturesque quality, bordered with carefully smoothed granite benches.

Glacier Lake

They also did a lot of bulldozing, moving piles of rocks and boulders from place to place.

An erratic boulder stranded in the middle of a glacially smoothed surface. Chain Lakes.

A terminal moraine of some small glacier

I saw an active glacier, Hinman glacier. It, along with all actively monitored glaciers in the Northern Cascades, is retreating. I was there in the
late afternoon, and there was a thundering roar of water pouring out from beneath the ice.

Black Smokers

After hiking out, I hitched a ride to the nearest truck stop with a man who had been helping out with his friend's gem mining operation (on private property, just outside the border of the Alpine Lakes wilderness area). He told me an interesting story:

The man who owns the mine, Bob, had been a geology student, researching the geologic history of the Middle Fork Snoqualmie River Valley. He learned that the area contained fossilized black smokers, rich in mineral deposits. [Basically the roots of these undersea hydrothermal vents, which extend for many miles below the surface, are rich zones of mineralization due to the circulation of heated, acidic sea-water. They have since been uplifted and metamorphosed into the Cascade Range.]

So, one day Bob went for a walk in the area and found one of these structures, a black smoker root extending up a cliff face. He found a piece of quartz and pyrite. When he returned to the road, someone offered him 2,000 dollars for it and he's been (profitably) mining the area for gem quality crystals since then.

I saw a lot of quartz, no pyrite. I'm unsure what this one was...

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