Longitudinal dunes occur when sand supplies are limited.
The prevailing wind pushes the sand and forms long ridges that are parallel to the wind. In some areas the dunes can reach mass proportions of 100 meters in height and extend for 100 kilometers. However, the smaller types of longitudes dunes are a mere 3 to 4 meters high. You will find the larger dunes in North Africa, Central Australia, and Arabia. Click on photo to view enlargement.