I. The Mecklenburg County Greenway System
The Mecklenburg County Greenway system is quickly becoming one of the finest in the country. Greenways are vegetated natural buffers that improve water quality, reduce the impacts of flooding, and provide wildlife habitat. Greenway trails provide recreation, transportation, fitness, and economic benefits for all to enjoy. There are over 35 miles of developed greenways in Mecklenburg County. [http://charmeck.org/mecklenburg/county/ParkandRec/Greenways/OpenGreenways/Pages/default.aspx]
Note: this Greenway floods easily after big rains. If the path is flooded, it’s best to wait for another day.
II. Clast sizes
[from http://www.scienceviews.com/geology/sedimentary.html]
Fragments produced by the the weathering of rock are called clasts, which come in different sizes (see chart). Sand is one of these sizes, but here’s the thing about sand (or any of the other clasts)--Sand is a size and not a composition! Think of sand as just tiny rocks.
The type of sand you see depends entirely on the surrounding rocks. The black sand beaches of Hawaii result from the weathering and erosion of basalt. The green sand beaches of Hawaii result from the weathering of rocks high in olivine, typically a green mineral. The dunes of Coral Pink Sand Dunes in Utah are composed of quartz weathered from the surrounding sandstones.
The rocks in the area drained by Six Mile Creek are predominantly igneous and metamorphic--rocks abundant in the minerals quartz and various feldspars (e.g. - orthoclase and plagioclase). A lot of Mecklenburg County is underlain by a 400 million year old granite, which is pinkish gray, massive to weakly foliated; and contains hornblende. [from http://mrdata.usgs.gov/geology/state/sgmc-unit.php?unit=NCDOg%3B6]
For a more complete list of rocks of Mecklenburg County, go to http://mrdata.usgs.gov/geology/state/fips-unit.php?code=f37119 or get ahold of the geologic map, “The Charlotte 1 degree X 2 degree Quadrangle, North Carolina and South Carolina.”
You have sand at your house, too. The salt in your salt shakers is sand-sized. Sugar is sand-sized. That cereal that got crushed and lies at the bottom of the bag is usually sand-sized (e.g. - Life Cereal sand). You can make your own sand--all it takes is a hammer, a little time, and, possibly, some anger.
III. A terrifying, true sand story
[from http://fun.familyeducation.com/images/colored_sand_000000758823_H.jpg]
A few years ago, I was at an outdoor festival and walked up to a vendor selling different colors of sand that could be put in small jars to make patterns. Being a big fan of sand, I said, “What kind of sand is this?”
The vendor responded, “It’s just sand.” Then I had to give a furious geo-lecture about how sand is a size and and not a composition.
Long story short: I’m not allowed back at that festival.
IV. Rough Sand Identification Guide to Minerals in This Area.
This Guide is based on the presence of many igneous and metamorphic rocks in the watershed drained by Six Mile Creek.
Black and flakey (peels into thin, paper-like sheets) = biotite, a type of mica.
Black and not flakey = hornblende.
Light colored and flakey = muscovite, another type of mica.
Tan to brown and not flakey = quartz.
White or pink and not flakey = various feldspars.
V. Why is the Sand There At GZ?
The sand pile at between the edge of pavement and the creek is part of a natural levee created by flooding.
When the creek floods after a big rain, sediment from the creek is deposited on the floodplain, the flat land beside the creek. Because sand is bigger than silt- and clay-sized clasts, the sand is not carried so far from the creek by the flood waters and is deposited closer to the creek building up a small ridge, or levee, on the creek bank.
If you look in the creek bed, you can see the pebble- and cobble-sized clasts, which are much tougher for the creek to transport, so rarely get picked up and deposited on the floodplain.
[from http://www.coolgeography.co.uk/GCSE/AQA/Water%20on%20the%20Land/Meanders/Landforms%20Meanders.htm]
VI. A Heads Up for Wheelchairs and Strollers
This Earthcache is wheelchair and stroller accessible along a flat, asphalt-and-boardwalk path until the final 20 feet to the top of the small levee. There is some sand at the edge of the pavement, so it’s possible to still do this Earthcache from a wheelchair if you can reach down to the ground. Keep in mind that the distance from the parking lot to GZ is almost a mile.
Questions/Tasks
Please give the name of this Earthcache when you send your answers.
1. Grab a handful of sand from the Creek bank. Sometimes the sand can be hard packed, so you may need some kind of sand digging tool--maybe a stick. Examine the sand carefully with your magnifying glass.
2. List the minerals you see in your sand.
3. Give the percentage of each mineral that composes the sand you have in your hand. For example, Hawaiian beach sand might be Pyroxene = 70%, Olivine = 25%, and Coralline Algae = 5%.
4. What size clasts would you expect to find in the swamp on the floodplain on the other side of the paved walkway?
5. Why do you say that in #4?
6. (Optional) Did you see any animals on your hike? Feel free to post photos.
7. (Optional) Feel free to post a photo of you looking happy be there at GZ.