The type of dune that forms at right angles to the wind when there is abundant sand, a lack of vegetation, and a constant wind direction is called a transverse dune.

Here's why:

* Abundant sand: Provides the material to build the dune.

* Lack of vegetation: No plants to disrupt the wind's flow or hold the sand in place.

* Constant wind direction: The wind consistently pushes the sand in the same direction, leading to the formation of a ridge perpendicular to the wind flow.

Transverse dunes are often found in areas with large sand supplies, such as deserts or coastal regions. They are characterized by their distinctive crescent shape, with the horns pointing downwind.