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DIVISION OF GEOLOGY AND MINERAL RESOURCES

Identifying Geologic Landforms with LiDAR

A landform is defined as a naturally occurring feature of the surface of the earth. The Earth’s landscape, or terrain, is composed of landforms, and their arrangement in the landscape is better known as topography. Here are some examples of landforms that geoscientists can see in 1-meter LiDAR derived data.


Meander Cutoffs

Rivers are constantly evolving and moving their position on the surface of the earth in order to maximize the efficiency of water transport. As a meander (or hook) in a river is abandoned, the channel fills with sediment, leaving a record of their past location. These deposits are clearly visable with 1-meter LiDAR derived data.

Meandering cutoff

Meander cutoff

Braided Streams

The image below shows a “braided” stream in Tazewell County. This stream has rapidly shifted its channel in recent geological history because the small but very steep streams draining the surrounding mountains supply it with more sediment that it can transport. When the actively flowing stream channel becomes choked with boulders and gravel, the stream will shift its channel slightly onto a more efficient path. This process produces the complex overlapping channels seen here.

Ancient braided stream valley Tazewell County, Virginia

Ancient Braided stream valley Tazewell County, Virginia

Flatirons

Mountains in the Valley and Ridge and western Blue Ridge provinces have developed on hard sandstone or quartzite that is more resistant to erosion than adjacent rock layers such as shale, phyllite, or limestone/dolomite. The layered nature of the sandstone and quartzite sequences that support the ridges is clearly visable on LiDAR hillshade maps. This image shows “flatirons” on the southeast face of Peters Mountain in Giles County. When parallel streams cut through tilted sandstone layers, the neighboring V-shaped valleys divide the sandstone slope into the triangular facets seen here.

Flatirons on Peters Mountain, Virginia

Flatirons on Peters Mountain, Giles County, Virginia

Marine Terraces

These features in the Coastal Plain geologic province are relatively flat, horizontal surfaces underlain by sediments that record a history of past sea level rise. Marine terraces often contain important natural resources like sand and gravel. Terraces like those exposed along the Pamunkey River in the image below are clearly visible with high resolution, 1-meter LiDAR derived hillshades= maps.

Several  levels of marine terraces along the Pamunkey River near Tunstall, Virginia

Several levels of marine terraces along the Pamunkey River near Tunstall, Virginia

Carolina Bays

The oval depressions on the image below are not sinkholes, but are depressions known as Carolina Bays. These features are found throughout the Atlantic Coastal Plain, and are typical oriented in a northwest-southeast direction. There is several theories on the formation of the bays; they may be the result of a meteorite impact crater, melting ice after the last glaciation, or the action of sea currents. How many Carolina Bays can you identify in the image below?

Carolina Bays in the Virginia Coastal Plain

Carolina Bays in the Virginia Coastal Plain

Ancient Sand Dunes

The elongate ridges that you see in this image represent old sand dunes along the Delmarva Peninsula. These relict sand dunes show how the shoreline has moved in response to sea level change over geologic time.

Ancient Sand Dunes

Ancient Sand Dunes

Want to learn more about how DGMR maps geologic landforms? Learn more »