Death Valley 04: Sand Waves 2

Image Commentary

In this view we start to get a feeling for the large scale of the dune field. It is literally miles in length and breadth, and the larger dunes in the centre of the field can rach heights of several hundred feet. In this image we also see the hills in the background to the east, where extensive erosion has taken place, and even today is taking place, as evidenced by the many gullies and valleys we see in the distance.

The story of this part of Death Valley is very much one of cycles of erosion and re-deposition. These cycles begin in the high mountains that surround the valley. These steep sided mountains are subject to short, but extremely high energy and violently corrosive rain-storms that strip tons of rock away every year. With no vegetation or soil to prevent them, torrential downpours create rushing torrents of water that roll and bounce boulders of amazing size towards the valley floor. As they tumble, they break down and spread much smaller grains all and sundry in a tumult of gravity and water driven chaos. But as these torrents eventually meet the sharp break of slope at the base of the mountain sides where the valley floor begins, they suddenly and rapidly loose their energy and ability to support their burdens of debris. With little or no energy remaining, the largest debris is immediately deposited on the valley floor whereas some of the lighter and smaller debris is transported further out on to the valley floor. This pattern of deposition creates features known as "alluvial fans" a physical phenomenum that is especially well developed in Death Valley (Images DV23 and DV20).

These fans in turn may be re-cycled by yet later generations of rivers and flash floods causing yet another cycle of erosion and depositon. Eventually these sediments coalesce into piles of loosely bonded pebbles, boulders and sand until finally the wind rather than water takes over as the primary mover of material. The wind however, only has strength to move the finest sandy material, transporting only as long as the strength (velocity) of the wind persists. When the wind drops, so does it's burden. Typically, changes in wind patterns occur predictively - and repetitively - where terrains change. As a result, piles of fine sand eventually build up at such dump sites, the Tucki Dune Field being one.

As a result of this process it is quite likely that the hills in the distance behind the dunes, are in part at least some of the source of the sand that now makes up the dunes.