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Rock Structure as a Landform Control As denudation takes place, landscape features develop according to patterns of bedrock composition and structure. In this example, weaker sedimentary rocks such as limestone, have been eroded away more rapidly than the resistant igneous rocks. Consequently, the more resistant rocks create the dominant landforms in this region. Rock Structure as a Landform Control Sandstone Butte, Sedona, Arizona Rock Structure as a Landform Control Landforms evolve through the slow erosional removal of weaker rock, leaving the more resistant rock standing as ridges or mountains. Arid Regions Sharply defined landforms result in arid, sparsely vegetated regions with horizontal sedimentary lithologies. Horizontal plateaus develop in contrast to near vertical cliffs. Two landforms also result - larger mesas represent remnants of resistant rock which are eventually further eroded into smaller buttes. Arid Regions In arid climates, distinctive erosional landforms develop in horizontal strata Arid Regions Buttes in Tunisian Desert Ca. 1990s Tatawin, Tunisia. Coastal Plains Coastal plains are found along passive continental margins that are largely free of tectonic activity. They are underlain by nearly horizontal strata that slope gently toward the ocean. Coastal Plains Development of a broad coastal plain. (a) Early stage - plain recently emerged. (b) Advanced stage - cuestas and lowlands developed. Sedimentary Domes A distinctive landmass type is the sedimentary dome, a circular or oval structure in which strata have been forced upward into a domed shape. Eroded edges of the steeply dipping strata create sawtooth ridges called hogbacks. Streams draining such domes also tend to form radial drainage networks. Sedimentary Domes Erosion of a sedimentary strata from the summit of a dome structure. (a) The strata are partially eroded, forming an encircling hogback ridge. (b) The strata are eroded from the center of the dome, revealing a core of older igneous or metamorphic rock. Sedimentary Domes A sandstone dome is orange in the early morning light, Valley of Fire State Park, Nevada Fold Belts Strata of the continental margins are deformed into folds along narrow belts during continental collision. Deep erosion of these simple, open folds in this landmass type produces a ridge-and-valley landscape. Fold Belts Stages in the erosional development of folded strata. (a) Erosion exposes a highly resistant layer of sandstone or quartzite, which controls much of the ridge-and-valley landscape. (b) Continued erosion partly removes the resistant formation but reveals another below it. Fold Belts Boulder Mountain is visible in the distance, above the cliffs of Antone Ridge and Death Hollow, near the headwaters of the Escalante River, Utah, USA. Fault Scarps Active normal faulting produces a sharp surface break called a fault scarp. Repeated faulting may produce a great rock cliff hundreds of meters high. Erosion quickly modifies a fault scarp, but, because the fault plane extends hundreds of meters down into the bedrock, its effects persist for long spans of geologic time. Fault Scarps (a) A recently formed fault scarp. (b) Despite continental denudation over several million years, the fault plane causes a long narrow valley bounded by a scarp. Fault Scarps Red Canyon Fault Line. Exposed Batholiths and Monadnocks Batholiths, large igneous intrusions, may eventually become exposed at the surface as overlying rocks are eroded away. Exposed Batholiths and Monadnocks Exposed batholiths: Batholiths appear at the land surface only after long-continued erosion has removed thousands of meters of overlying rocks. Small projections of the granite intrusion appear first and are surrounded by older rock. Eroded Volcanoes Once volcanoes become extinct and no longer supply fresh lava to the surface, environmental conditions will begin to promote their erosion. Stratovolcanoes may collapse to create a caldera crater, followed by the reduction of the landscape to a series of lava mesas. Eventually, little remains of the initial stratovolcano except dikes and a lava mesa. Eroded Volcanoes Shield volcanoes in various stages of erosion make up the Hawaiian Islands. (a) Newly formed dome with central depression. (b) Early stage of erosion with deeply eroded valley heads. (c) Advanced erosion state with steep slopes and mountainous relief. Eroded Volcanoes Mount Bromo, an eroded volcanic cone in Bali, Indonesia.