Welcome

Welcome to Arapaho National Forest. This EarthCache was placed with permission of the park so it is important that you follow all rules to demonstrate how responsible geocachers are with the environment. Please stay on the trail and follow all rules as posted. At no point, should you collect anything, or disturb the environment except where specifically directed. Please enjoy this EarthCache responsibly. 

Earth Science Lesson

Playa, (Spanish: shore or beach) , also called pan, flat, or dry lake, flat-bottom depression found in interior desert basins and adjacent to coasts within arid and semiarid regions, periodically covered by water that slowly filtrates into the groundwater system or evaporates into the atmosphere, causing the deposition of salt, sand, and mud along the bottom and around the edges of the depression.

Playas are among the flattest known landforms. Their slopes are generally less than 0.2 metre per kilometre. When filled with only a few centimetres of water, many kilometres of surface may be inundated. It is the process of inundation that develops and maintains the near-perfect flatness so characteristic of these arid-region landforms.

Playas occupy the flat central basins of desert plains. They require interior drainage to a zone where evaporation greatly exceeds inflow. When flooded, a playa lake forms where fine-grained sediment and salts concentrate. Terminology is quite confusing for playas because of many local names. A saline playa may be called a salt flat, salt marsh, salada, salar, salt pan, alkali flat, or salina. A salt-free playa may be termed a clay pan, hardpan, dry lake bed, or alkali flat. In Australia and South Africa small playas are generally referred to as pans. The low-relief plains of these lands contrast with the mountainous deserts of North America, resulting in numerous small pans instead of immense playas. 

Dry lake

A dry lake bed, also known as a playa, is a basin or depression that formerly contained a standing surface water body, which disappeared when evaporation processes exceeded recharge. If the floor of a dry lake is covered by deposits of alkaline compounds, it is known as an alkali flat. If covered with salt, it is known as a salt flat.

Terminology

If its basin is primarily salt, then a dry lake bed is called a salt pan, pan, or salt flat (the latter being a remnant of a salt lake). Hardpan is the dry terminus of an internally drained basin in a dry climate, a designation typically used in the Great Basin of the western United States.

Another term for dry lake bed is playa. The Spanish word playa (pronounced [ˈplaʝa]) literally means "beach". Dry lakes are known by this name in some parts of Mexico and the western United States. This term is also used on the Llano Estacado and other parts of the Southern High Plains.

In South America, the usual term for a dry lake bed is salar or salina, Spanish for salt pan.

Pan is the term used in most of South Africa. These may include the small round highveld pans, typical of the Chrissiesmeer area, to the extensive pans of the Northern Cape province.

Terms used in Australia include salt pans (where evaporite minerals are present) and clay pans.^[1]

In Arabic, a salt flat is called a sabkha (also spelled sabkhah, subkha or sebkha) or shott (chott). In Central Asia, a similar "cracked mud" salt flat is known as a takyr. In Iran salt flats are called kavir.

Formation

A dry lake is formed when water from rain or other sources, like an intersection with a water table, flows into a dry depression in the landscape, creating a pond or lake. If the total annual evaporation rate exceeds the total annual inflow, the depression will eventually become dry again, forming a dry lake. Salts originally dissolved in the water precipitate out and are left behind, gradually building up over time. A dry lake appears as a flat bed of clay, generally encrusted with precipitated salts. These evaporite minerals are a concentration of weathering products such as sodium carbonate, borax, and other salts. In deserts, a dry lake may be found in an area ringed by bajadas.

Dry lakes are typically formed in semi-arid to arid regions of the world. The largest concentration of dry lakes (nearly 22,000) is in the southern High Plains of Texas and eastern New Mexico. Most dry lakes are small. 

Many dry lakes contain shallow water during the rainy season, especially during wet years. If the layer of water is thin and is moved around the dry lake bed by wind, an exceedingly hard and smooth surface may develop. Thicker layers of water may result in a "cracked-mud" surface and teepee structure desiccation features. If there is very little water, dunes can form.

The Racetrack Playa, located in Death Valley, California, features a geological phenomenon known as "sailing stones" that leave linear "racetrack" imprints as they slowly move across the surface without human or animal intervention. These rocks have been recently filmed in motion by the Scripps Institution of Oceanography at UC San Diego and are due to a perfect coincidence of events. First, the playa has to fill with water, which must be deep enough to form floating ice during winter, but still shallow enough that the rocks are exposed. When the temperature drops at night, this pond freezes into thin sheets of "windowpane" ice, which then must be thick enough to maintain strength, but thin enough to move freely. Finally, when the sun comes out, the ice melts and cracks into floating panels; these are blown across the playa by light winds, propelling the rocks in front of them. The stones only move once every two or three years and most tracks last for three or four years.

Logging Tasks

Questions for Logging Credit:

1. Describe the lake bed in terms of sediment and rocks.
2. How deep does this lake get when filled with precipitation?
3. Where does the water for this formation come from?
4. Would you call this a playa, a dry lake, or a hardpan?
5. Was there any water in this landform during your visit?
6. Compare this to the lake at Stage 2 (depth, source, evaporation, rocks in the area)
7. Post a photo of yourself (or a proxy) at Stage 2.

References

1. ^ Twidale, C.R. & Campbell, E.M. (2005, revised edition): Australian landforms: understanding a low, flat, arid and old landscape. Rosenberg Publishing. Pp. 227, 235, 237, 239. ISBN 1 877058 32 7
2. ^ "Uyuni Salt Flat" Encyclopædia Britannica
3. ^ "Sliding Rocks on Racetrack Playa, Death Valley National Park: First Observation of Rocks in Motion". PLoS ONE. 2014-08-27. Retrieved 2016-06-23.
4. ^ "Ice rafts not sails: Floating the rocks at Racetrack Playa" (PDF). Barnesos.net. Retrieved 2016-06-24.
5. ^ Rogers, D. Christopher; Quinney, Weaver, Olesen (2006). "A New Giant Species of Predatory Fairy Shrimp from Idaho, USA (Branchiopoda: Anostraca)" (PDF). Journal of Crustacean Biology. 26 (1): 1–12. doi:10.1651/C-2509.1. Retrieved 2 May 2014.
6. ^ Jump up to:^{a b} Hagwood, Sheri. "Sensitive Plants of the JRA" (PDF). Idaho BLM. Archived from the original (PDF) on 3 May 2014. Retrieved 2 May 2014.
7. ^ "CRS Report for Congress: Agriculture: A Glossary of Terms, Programs, and Laws, 2005 Edition - Order Code 97-905" (PDF). Archived from the original (PDF) on August 10, 2011. Retrieved November 30, 2009. A temporary lake created in the lowest elevation of a basin in an arid area that has no surface drain into another water body, such as a perennial stream or river. Lake water is removed either by evaporation into the air or seepage into the ground.
8. Briere, Peter R. (May 2002). "Playa, playa lake, sabkha: Proposed definitions for old terms". Journal of Arid Environments. Elsevier. 45 (1): 1–7. doi:10.1006/jare.2000.0633.
9. John H. Wellington, Southern Africa: a geographical study, Chapter 16 LAKES AND PANS