Desert pavement and ventifacts EarthCache

Introduction

At the coordinates the desert floor is covered with pebbles of which some have strange flat side(s). This cache intends to show how the desert floor became covered with these pebbles and how the strange stones are created.

General

The Qatari desert is part of the Arabian desert [ ] encompassing almost all of the Arabian peninsula.

This desert is located on a low-altitude, which is the main cause of desertification: Hot air at the equator rises and spreads out in the directions of the tropic of cancer and Capricorn. Between 20° and 30° latitude the air starts to sink and is compressed and warmed: the opposite conditions of what's needed for clouds and precipitation. Thus resulting in a hot dry area with clear skies, hot sunny weather and ongoing drought.

Desert erosion

Water
Despite popular belief, running water is the main agent of erosion in desert, albeit infrequent.

Because of a lack of vegetation and moisture, most of the surface material is not anchored. If it rains, the water scoops up loads and loads of the loose material and does an impressive amount of erosional work in a very short time span. As example have a look at the gully, some 40m away (waypoint RP21X00).

This also explains why wadi's are never crystal clear streams: the water is saturated with material.

Wind
Wind, just like water, is able to pick up and transport material. In areas where moisture is retained in the soil and a lot of vegetation exists, there's not a lot of loose material to be swept up by the wind and therefore wind-erosion is very limited.

In an arid desert environment, with lack of moisture, hardly any vegetation and thus an abundance of loose material, wind is an important erosional agent.

Sediment transport by wind

Suspended load
Dust (silt and clay) usually is rather flat and has a large surface area compared to its weight. Turbulent air can fairly easy counter the effects of gravity and take the dust particles much higher into the atmosphere, keeping it there in suspension for hours or even days, moving the dust away from its origin.

Bed Load
In running water, the bed load are particles transported along the bed (bottom) by rolling or hopping. Analogue to water, wind can carry a bed load as well: Small particles, sand, are rolled over the surface. Initially, at lower wind speeds, this process is called creeping. When the wind speed increases, particles start rolling faster. When a sand grain strikes another grain, it can jump up in the air and be carried forward by the wind, until gravity pulls it back to the surface. When the sand grain hits the surface again, it can dislodge other grains, which bounce up in the air, thus causing a chain reaction filling the air near the ground with saltating grains of sand, usually a layer of about half a meter thick.

This process is called saltation [ ] a word derived from the latin 'saltus' which means to jump or leap.

On windy days this can be seen by 'sheets' of sand being blown along the desert floor.

Desert pavement

At GZ the desert floor is largely a layer of pebbles (and cobbles) and is a result of a process called deflation.

The wind lowers the terrain by removing dust and sand particles until only a layer of closely packed pebbles remain. In turn this layer now protects the underlaying sand and dust and in effect ending the deflation process.

Ventifacts

On top of the desert pavement you can find pebbles with one or more perfectly flat sides. These rocks are called ventifacts and are created by the bedload in the wind. The saltating sand grains keep bumping into a pebble and through abrasion polish the side of the rock in the prevailing wind, creating a flat surface with sharp edges.

If the wind regularly blowing from different directions or if a ventifact is reoriented, multiple sides are polished to a flat surface.

Note: I've spotted just a few ventifacts in the area around the coordinates. Please leave them in place as they are.

Logging this earthcache

You may log the Desert pavement and ventifacts earthcache immediately after visiting, but I'll require the answers to the questions below within a reasonable time frame.

Please send me the answers, preferable in English, through my contact page and please tick the "I want to send my email address along with this message.", so I can reply directly.

Hints, Tips & the rest

• 4x4 vehicle is required to reach this spot.
• Bring enough water and preferable do not travel with a single car.