A butte is an isolated hill characterized by steep sides and a small, flat summit. This landform is a product of long-term geological processes and is typically found in arid regions, such as the American Southwest. Geologically, a butte is an erosional remnant, the last portion of a larger landmass remaining after the surrounding material has been worn away.
Physical Characteristics of a Butte
A butte’s appearance is defined by its vertical structure and layered composition. The sides of the landform are steep or nearly vertical, forming what geologists call escarpments. These sheer faces descend to a base where rock debris, known as a talus slope, has accumulated from continuous weathering.
The summit of a butte is small and flat, significantly narrower than the landform’s height. This dimensional ratio establishes the butte as a tower-like structure that is taller than the width of its top. The flat top surface is composed of a layer of highly resistant rock, known as the caprock.
The Geological Process of Formation
Buttes are created by the geological process known as differential erosion, which involves the uneven wearing away of rock layers with varying resistance. This process begins when a layer of hard caprock, such as dense sandstone or basalt, covers underlying layers of softer, less resistant sedimentary rock. Over millions of years, water and wind act on the landscape, slowly stripping away the exposed, softer material.
The durable caprock shields the column of softer rock directly beneath it from the elements. As the surrounding terrain erodes downward, the protected column is left standing in isolation. This occurs when streams and other erosional forces cut through the wider plateau, separating a section.
This mechanism continues until the caprock is breached or undercut, a process that can take thousands to millions of years. Once the protective cap is compromised, the softer rock below begins to erode more rapidly, causing the steep sides to retreat and the butte to diminish in size.
Comparing Buttes to Mesas and Plateaus
Buttes are commonly confused with two other flat-topped landforms, mesas and plateaus, but the distinction is primarily one of size. A plateau represents the initial, largest form, consisting of an extensive, raised area with a flat top and steep sides. Plateaus represent the bedrock from which the other forms are carved.
A mesa, which is Spanish for “table,” is a broad, flat-topped landform that is smaller than a plateau but larger than a butte. Geographers use a dimensional rule to separate these two: a mesa’s summit is wider than its height. A butte represents the final stage of this erosional progression, reduced to the point where its height now exceeds the width of its top.