Thursday, August 30, 2007

Can You Solve the Mystery at the Alluvial Fan?

Since we spent 3 days in RMNP last summer, we wanted to do new things. Last year ds did an excellent, thorough job on the Junior Park Ranger activity booklet. When he turned it in to the ranger the day we left, he was sworn in as a junior ranger. This year upon arrival, I scoured the ranger store for ideas. On the shelf I found a little booklet called "Trouble in the Rubble," a mini-field trip guide teaching the geology of the RMNP alluvial fan.

The book had a story about kids trying to solve a mystery, and our kids were invited to join. The mystery was that a boy found a treasure map from 1884 locating gold near the alluvial fan. Historically, gold prospecting was successful in parts of Colorado. Was there any in RMNP? Was this map real?

When you look around you see lots of boulders laying around and felled trees. You see the water falling down the valley and the rapidly flowing stream. It continues downhill to Horseshoe Park and continues as Fall River into Estes Park. We learned how to measure our paces so we could mathematically count the steps from one large boulder to another.

Alluvial Fan RMNP 2007
Then we looked at the various shadings for each boulder on the map and learned about the type of rock of each: silver plume granite,

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pegmatite,

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mica schist, and gneiss (nice). The kids were already familiar with how each rock was formed. Granite and pegmatite are igneous rocks, having been formed by volcanic activity, which formed the Rocky Mountains. Schist and gneiss are metamorphic rocks, having been changed in compostion due to heat or stress. They were also familiar with the names because of our rock collection at home. But now they had the opportunity to apply that knowledge.
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There certainly were some shiny rocks. We concluded they were mica schist, a type of metamorphic rock which often fooled gold prospectors.

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Another clue was the gouged out part of the rock, gneiss. This is formed by turbulently swirling waters that are full of pebbles. The pebbles act like a drill, caused by the momentum of heavily swirling water. As the hole got bigger, bigger rocks got stuck in the swirling process, causing a bigger pothole, which this feature is called.

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Historically, this is a flood area. Above us in the alpine area, is Lawn Lake which used to be dammed. In 1982, that dam broke and within minutes the landscape was changed by a deluge of water. Boulders left in the higher altitudes of Lawn Lake by glaciers tumbled down, clearing the path of trees and forming a V shaped valley which now contains a water fall. The flood waters continued down Fall River into town. Unfortunately a few lives were lost. The resulting scar on the bottom of the mountainside was an alluvial fan.

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From a creationist viewpoint, this is a perfect example of how a flood can destroy things quickly. Water did not erode that pothole in millions of years, it happened in minutes. Awesome from a geological viewpoint!

From the activity we learned that these 4 rocks are the only 4 rock types in the entire park. Ah! We could actually drive around this year, knowing a little something! We spent about an hour climbing around looking at the alluvial fan with new eyes. We could appreciate the new plant life emerging from the destruction. Here is some Russet Buffaloberry...

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Changing leaves...

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Fireweed...
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Baby pine trees...

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Oh, and the mystery? One of the give away clues to the 1982 flood was the trapped logs under some of the boulders. No, this cannot be an accurate map, because this is not where the boulders were in 1884. Case solved!

1 comment:

  1. Sounds fun! I think I'll have my kids come read your blog today and count it as science. =)

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