Butte (géomorphologie)

NOTOC In geomorphology, a butte (bjuːt) is an isolated hill with steep, often vertical sides and a small, relatively flat top; buttes are smaller landforms than mesas, plateaus, and tablelands. The word butte comes from the French word butte, meaning knoll (but of any size); its use is prevalent in the Western United States, including the southwest where mesa (Spanish for "table") is used for the larger landform. Due to their distinctive shapes, buttes are frequently landmarks in plains and mountainous areas. To differentiate the two landforms, geographers use the rule of thumb that a mesa has a top that is wider than its height, while a butte has a top that is narrower than its height. Buttes form by weathering and erosion when hard caprock overlies a layer of less resistant rock that is eventually worn away. The harder rock on top of the butte resists erosion. The caprock provides protection for the less resistant rock below from wind abrasion which leaves it standing isolated. As the top is further eroded by abrasion and weathering, the excess material that falls off adds to the scree or talus slope around the base. On a much smaller scale, the same process forms hoodoos. The Mitten Buttes of Monument Valley in the Utah-Arizona state line are two of the most distinctive and widely recognized buttes. Monument Valley and the Mittens provided backgrounds in the scenes of many western-themed films, including seven movies directed by John Ford. Another very well-known and frequently photographed butte in northern Arizona is Thumb Butte, which overlooks the city of Prescott and is the most prominent and distinctive geologic landmark in the vicinity. The Devils Tower in northeastern Wyoming is a laccolithic butte composed of igneous rock rather than sandstone, limestone or other sedimentary rocks. The term butte is sometimes applied more broadly to isolated, steep-sided hills with pointed or craggy, rather than flat, tops.