I’ve studied sand dunes for 40 years – here’s what people find most surprising

By David Thomas, University of Oxford

The Dune films remind us of just how beautiful, mysterious, expansive and changeable sand dunes can be. For centuries these wonderful landforms have filled humans with awe – and in some cases fear and foreboding – because of the apparent remoteness and risks associated with the deserts they are synonymous with.

That’s what first attracted me to research deserts and dunes more than 40 years ago, and I have been investigating them ever since. Here are five things I have learned that may surprise you:

Not all dunes are made of sand

Ash, snow and even gypsum can all build dunes. Dunes develop when small particles are mobilised on bare dry surfaces by a moderate wind, accumulating where movement is slowed down by an obstacle or a surface undulation. Where the wind deposits the particles they can create a small mound against which other particles in turn accumulate, leading eventually to a dune.

“Sand” is not really a material – it is a size of particle, somewhere between 0.06mm and 2mm diameter. Dunes in deserts and at the coast are primarily formed of quartz and feldspar grains, the most common minerals on earth.

But in volcanic regions, such as the interior of Iceland, dunes can be formed of ash, while in the centre of Antarctica, the driest and windiest continental earth, dunes can form from ice crystals and snow. In New Mexico, US, the very soft and bright mineral gypsum forms dunes – appropriately the place is called White Sands.

Dunes can record a history of climate changes

Sand dunes might seem soft and changeable, but below their active surface there often lies older sand that tells a story of long-term development.

Dune shape is affected by how changeable wind direction is through the year: some dunes, such as crescent-shaped barchan dunes, roll forward under fairly consistent winds, with the sand turning over on a regular basis.

Read Full Story https://theconversation.com/ive-studied-sand-dunes-for-40-years-heres-what-people-find-most-surprising-226680