Mesa

A mesa is an isolated landform with a flat top and steep sides. It stands distinctly above the surrounding plains or lowlands. These landforms are often ridges or hills bounded by steep escarpments. The term mesa comes from the Spanish word for "table." In 1922, the geologist Kirk Bryan described them as standing like a table on a floor.

Mesas form through a geological process called differential erosion. This happens when different types of rock wear away at different speeds. Mesas are made of horizontally layered sedimentary rocks that were once uplifted by tectonic activity. Harder rocks resist weathering, while softer rocks break down more easily. This difference in strength creates the distinctive shape of the mesa. The harder layers stay high, while the softer layers are carved into valleys.

Every mesa features a protective top layer known as a caprock. This caprock is made of highly resistant rock like sandstone, limestone, or conglomerate. It can also consist of quartzite, basalt, or even hard lava flows and sills. Beneath this caprock lie softer, less resistant layers such as shale. The caprock shields the underlying layers from eroding too quickly. This protection allows the summit to remain flat and elevated.

As erosion continues, the sides of a mesa develop a specific look. Instead of smooth slopes, they often show a "cliff-and-bench" topography. The resistant rock layers form steep cliffs, while the softer layers form gentle slopes called benches. These cliffs move backward over time through a process called basal sapping. Water flows around the rock layers or moves through permeable layers as groundwater. This water erodes the soft shale at the base of the cliffs. Eventually, the underlying shale can no longer support the heavy rock above. This causes the cliff layers to slump and collapse.

Geologists use different names for similar landforms depending on their size and shape. A mesa is larger and has a more extensive summit than a butte. A butte is essentially a mesa that has eroded until very little caprock remains. A plateau is a much broader, elevated region that may not have horizontal bedrock. If the rock layers are tilted, the landform is called a cuesta, which has one steep side and one gentle slope. In Venezuela, these flat-topped mountains are known as tepuis. In Australia, they are sometimes called tablehills or jump-ups.

Mesas vary greatly in size across the globe. In the Cockburn Range of Australia, mesas can cover areas as large as 500 square kilometers. Conversely, in the Elbe Sandstone Mountains of Germany, mesas can be as small as 0.01 square kilometers. The Grand Mesa in Colorado is noted as the largest flat-topped mountain in the world. You can find these formations in many places, including Arizona, Utah, and Israel. They also appear in the United Kingdom, such as in North Yorkshire and Cumbria.

These landforms are not unique to Earth. Scientists have observed mesas on the planet Mars. In a region called Noctis Labyrinthus, there is a transitional zone known as fretted terrain. This area contains steep-walled mesas and knobs located between highlands and lowlands. Researchers believe these Martian mesas may form from mass wasting processes involving ice. This shows that the same physical principles of erosion can shape landscapes on other worlds.