TIME
When most people look at the Grand Canyon, they see the result of changes that took millions of years to occur. This EarthCache is centered on a change that took only hours.
DEBRIS vs MUD FLOWS
DEBRIS FLOW
A DEBRIS FLOW is a moving mass of loose mud, sand, soil, rock, water and air that travels down a slope under the influence of gravity. To be considered a debris flow, the moving material must be loose and capable of “flow”, and more than half of the solids in the mass must be larger than sand grains, including gravel, pebble, cobble and boulder sized material. The speed of a debris flow can reach of 100 miles per hour.
MUD FLOW
A MUD FLOW is a mass of water and fine-grained earth materials that flows down a stream, ravine, canyon, arroyo or gulch. A mud flow is a mass of water and sand-sized or smaller particles that can flow very rapidly. To be considered a mudflow, more than half of the particles must be sand sized or smaller. Mud flows are the sandy, more watery counterparts of debris flows.
CHARACTERISTICS
Debris and mud flows are a combination of fast moving water and a great volume of sediment and debris that surges down slope with tremendous force. The consistency is like that of pancake batter. They are similar to flash floods and can occur suddenly without time for adequate warning. When the drainage channel eventually becomes less steep, the liquid mass spreads out and slows down to form a part of a debris fan or a mud flow deposit. In the steep channel itself, erosion is the dominant process as the flow picks up more solid material.
WHY HERE?
On July 27, 1984, a thunderstorm centered on Monument Creek and dropped a torrential downpour. The creek quickly brimmed with raging water. Side washes, above the creek, filled with water and rushed over cliff edges, triggering an avalanche of rock, mud, and water that fell nearly 2,000 feet into the canyon. The creek turned into mud and rock slurry, flowing like freshly poured concrete with huge boulders bobbing on its surface. The slurry raced 3 miles to the creek mouth, spilling its load into the Colorado River and on Granite Rapid.
LOGGING REQUIREMENTS
In order to claim credit for this EarthCache, send answers to the following questions to me either through email or messaging from my profile page. Please DO NOT post the answers with your online log.
1: Was the event on July 27, 1984 a debris or mud flow?
2: What size (diameter and weight) were the boulders deposited by the flow in 1984?
3: Look around the canyon from the posted coordinates. Do you see any areas that could become a mud or debris flow? Please describe the materials that would be part of the flow and if it would be classified as a debris or mud flow.
4. Pictures are not required but are always appreciated. Please post a pic of you or your GPS at the posted coordinates with the canyon in the background.
NATIONAL PARK SERVICE POLICY
In accordance with National Park Service Policy review on "GPS-Based Recreational Activities in National Park areas" updated October 1, 2009, this EarthCache does NOT require or encourage participants to leave the marked trail, move, touch, or in any other manner disturb the natural environment. Please use caution and stay at least 6 feet away from the edge of the canyon at all times. EarthCaches are a type of geocache that may provide participants with a learning experience in the geosciences, and do not involve a physical cache.
This EarthCache was developed in cooperation with and with written permission from the Grand Canyon National Park.