After our horseback ride and lunch, the weather suddenly turned cloudy and chilly. We put on our coats and set out to tour the Alluvial Fan.
Alluvial Field Guide for Children
The other day at the park ranger shop I had purchased a mini-field trip guide teaching the geology of the alluvial fan: Trouble in the Rubble.
In the booklet was a story about kids trying to solve a mystery and our kids were invited to join. The mystery was that the boy had found a treasure map from 1884 locating gold near the alluvial fan. Historically, gold prospecting was successful in different areas of Colorado, like Cripple Creek, which my kids and I visited in 2001.
Was there any gold in RMNP? Was this map real? My kids had lots of fun scrambling the rocks. We spent part of this afternoon until rain chased us away, and part of the next morning, working through the clues.
Clue: Obvious Destruction
Even if not doing this field guide for kids, everyone notices the triangular shaped area of huge boulders and felled trees. Also quite noticeable is the water tumbling down the valley into a rapidly flowing stream, that continues downhill to Horseshoe Park (where we had earlier ridden our horses) and on to Fall River into Estes Park.
We learned to measure our paces in such a way that we could mathematically count the steps from one large boulder to the next.
Types of Rock in RMNP
While we looked at the various shadings of color on each boulder, we learned the types of rock of each: silver plume granite, pegmatite, mica schist, and gneiss (pronounced like nice).
Already familiar with these types of rocks, we were excited to discover these are the four dominant types of rock found in the entire park. That will be easy to remember this week!
While analyzing these rocks, we focused on the glittery ones, which we knew to be mica schist, a metamorphic rock which often fools gold prospectors.
Clue: Gouged Rock
Another clue was the gouged-out part of this rock, gneiss. This was formed by turbulently swirling waters that are full of pebbles. The pebbles act like a drill, causing the momentum of the swirling water. As the hole got bigger, bigger rocks got stuck in the swirling process, causing a bigger pothole, which this feature is called.
1982 Lawn Lake Flood
Historically, this is a flood area from 1982 when the dam burst at Lawn Lake. Within minutes after the dam breaking, a deluge of water poured down into this area and the landscape was changed.
And now for the rest of the story:
Lawn Lake Dam, which was built in 1903 for irrigation, fell within the jurisdiction of Rocky National Park when it was established 12 years later.
Naturally a glacial-formed lake, Lawn Lake was set at 11,000’ from which the Roaring River meandered to Fall River in the valley below, to the nearby town of Estes Park.
In 1931 the dam was raised, which significantly increased the amount of water in the lake.
Despite being forewarned in several inspections from 1951 through 1978 of various issues needing attention, the difficulty in accessing the remote location resulted in postponing action.
Suddenly on July 15, 1982, between 5-6am, the dam burst, releasing a massive wall of water roaring down a vertical 2500’ drop over 4.5 miles via the Roaring River Channel that flooded the flat basin of Horseshoe Park.
Areas 50 feet deep were eroded, while a massive amount of boulders that ripped out trees created an Alluvial Fan over an area of 40 acres.
However the wall of water roared through the basin to the Cascade Dam, which the water overtopped at 17 feet high, destroying that dam and excessively enlarging the flood surge.
Flood waters filled the town of Estes Park, leaving water five feet high.
Alerted by an early morning garbage man, park personnel began emergency alerts. Three campers died. Damages totaled in the millions.
Rapid Flooding causes rapid destruction
From a Young Earth viewpoint, this is an example of how a flood can destroy things quickly. Water did not erode this area gently and slowly in millions of years, but forcefully in minutes.
The first several roadside stops on Trail Ridge Road afford mountaintop views of the Alluvial Fan.
Stay tuned for more of our journey on Trail Ridge Road, which took us to the tundra!
For more photos of the Alluvial Fan, check my Flickr set by clicking on any of the photos.
