The Phenomena of the Martian Sand Dunes—Part III
Science divides the sand dunes up into several different types of categories, based on their shape and how they were formed. This depends on the ability of the winds to pick up/carry sand, and also the direction of which the Martian wind is blowing. These types are the Barchanes, Parabolic, Transverse, and the Longitudinal sand dunes.
BARCHANS – The Barchans sand dunes are crescent in shape and made of well-sorted sand, formed by winds that are blowing in one continuous direction over low areas of sand. With two “horns” or points facing downward, the steeper and taller middles ones are facing into the arising wind. The downward slope’s angle of repose is approximately 32 degrees, while the upwind side stands about 15 degrees, packed by the wind. Appearing larger, this type of sand dune may migrate with the wind, coalescing into ridges that extend for hundreds of miles. One of the types which appear on Mars, this is formed by the thin atmosphere, producing fierce winds that move the sand and dust over the surface of the red planet.
PARABOLIC—The Parabolic sand dunes are U in shape, with convex noses trailed by elongated arms trailing behind. Other names in addition to parabolic are “U-Shaped, blowout, or hairpin” and are well known both on Earth coastal deserts and on Mars. Different than the crescent shaped dunes, their crests will point upwind. On Earth, Parabolic sand dunes can be located at the Great Sand Dunes formed because the sand sheet is covered with growing vegetation. On abundant sand beaches, winds are more moderate in strength while tending to blow from the same direction s as blowout parabolic dune.
TRANSVERSE—The Transverse sand dunes blow in a continuous direction with an apple supply of sand, making long crests and troughs, located right angles to the wind while appearing as if they were waves upon the sea. The accumulations of sand are loose and well-sorted, from medium sand on down to very find sand. Their slopes are formed with a gentle upwind with less than 15 degrees and a 32 degree slip face on the lee slope. Perpendicular to the wind direction are long axes of the ridges that are relatively straight or slightly curved—appearing as linear dunes—except the transverse ridge has two different angles of slope, and the upwind slope’s sand is firmly packed while the avalanche slope (or steeper lee slope) is soft and loose sand. Also, the transverse dunes migrate laterally toward the next dune ridge, as compared to longitudinally down the ridge’s long axis.
LONGITUDINAL—The longitudinal dunes flow in the same direction as the wind, with a low sand supply and strong winds. Also called the Seif dunes, this type of dune occurs when there is a short supply of sand, or when barchans dunes become elongated. During this time, they may also be referred to as “linear dunes.” On Earth, this is the most widespread type of dunes in our deserts.
This entry was posted on Sunday, April 27th, 2008 at 1:08 pm and is filed under Mission Objectives, Space Agency News. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
