This Earthcache will introduce you to some of the geological features at Tanyard Creek Nature Trail. Take the time check out the other great Earthcaches / Traditional Caches. Parking and Trailhead waypoints are provided.
As with all Earthcaches, there is no physical container to find here. TO LOG THIS EARTHCACHE, YOU MUST EMAIL ANSWERS TO THE QUESTIONS FOUND AT THE BOTTOM OF THIS PAGE. Found logs without emailed answers will be deleted!
What is Alluvium?
Alluvium is loose soil or sediment that has been eroded, reshaped by water in some form, and redeposited in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel. When this loose alluvial material is deposited it is called an alluvial deposit.
I'm a Fan of Alluvial
An alluvial fan is a fan or cone shaped deposit of sediment built up by flowing water. This flow comes from a single point source at the apex, or start of the fan. An alluvial fan is usually found where a canyon or restricted channel opens out onto a flat plain. In this case the source is spring water flowing from the cave. As the spring water flows along its path of least resistance the sediment fans out over time. Alluvial fans happen on all scales from tens of feet to kilometers, the largest fans are normally in arid climates where there is little vegetation to hold back erosion. The largest are called "Megafans", covering up to 15,000 square kilometers over thousands of years. In a humid climate like NW Arkansas the fans tend to be smaller and are affected by the steepness of the gradient where they are formed.
The diagram below is an example of an Alluvial Fan.
Out of this world bonus info!
NASA has discovered evidence of alluvial fans on the surface of Mars supporting the theory that liquid water was once present in some form on the Martian surface.
On Dec 8, 2020 Groundspeak announced Earthcaches including Planetary Geology on Earth. Coincidentally, when this cache was originally published in 2018 it included the connection to Mars and the link in the sources. I added the image below on Dec 2020.
The image below is from the Saheki Crater on Mars showing an Alluvial Fan.
Observations at the posted coordinates
At the posted coordinates you will find spring water flowing from a fissure cave. This is the discharge area for water that has collected from a series of underground passageways formed in the karst through chemical weathering. Near the entrance of the cave there is evidence of an Alluvial Fan where spring water deposited sediment. You will also find evidence of an old homestead. There are ruins of an old pump house foundation and pipes that were used to supply water to the home.
To qualify for this Earthcache send me an email or message via my geocaching profile with the answers to the following questions. Please include the name of the cache along with your answers.
Do not post the answers in your log. Photos are encouraged!
To answer the questions, it is not necessary to enter the cave or get wet.
- At the posted coordinates you will find the spring water flowing out of the Tanyard Spring cave, Provide the dimensions of the cave opening.
- According to the sign near the cave entrance, about how old is the alluvium deposit and what caused it?
- What kind of debris is in the alluvium deposit? Is it loose or compact?
- How could the housing at the top of the hill effect the spring water, cave, and alluvium deposit?
Sources
Wikipedia - Alluvium
Wikipedia - Alluvial Fan
National Geographic
NASA - Martian Alluvial Fan
