Development of rill marks on the beach face at Galveston Island State Park, Texas

• In Event: Geosciences: Oral session 1

Abstract

Well developed rill marks are present on the beach face at Galveston Island State Park, Texas. These rill marks are produced as the tide goes out by water draining from the berm and bars that are found on the beach face. They develop in zones where there is a higher permeability in the berm and bars that run parallel to the beach face. These zones contain course clasts and fossil fragiments and a small amount of clay. Below and above each permeable zone, the sand contains fewer large clasts and shell fragments and larger amounts of clay resulting in the zone being less permeable. Rill marks are produced by a thin film of water that flows out of the sand and down the beach face following the breaking of each wave as the tide goes out. Rill marks are divided into five different types: fringy, conical, branching, meandering, and bifurcating. All five types of rill marks are found on the beach face at Galveston Island State Park. The type of rill mark present is determined by: the angle of the slope on the berm and bar face, the amount of porosity and permeability of the sand, and wave impact direction and intensity. They are best developed on stormy days with high tides. Rill marks are rarely preserved in the rock record because the next high tide destroys the rill marks that developed during the last low tide.

Author

• Russell LaRell NIelson, Stephen F. Austin State University