Chapter 23 Tectonics and Landforms

Climate

Differential Erosion

Evolution of Shields Early Stage – maximum relief, thrust faults, folds dominate, Andes Mountains Erosion, isostatic rebound, folds exposed at surface, Appalachian Mountains Continued erosion and isostatic adjustment, deep folded rocks exposed at surface, Scotland, Norway Isostatic equilibrium is established, Canadian Shield

Rates of Erosion of Mtn. Belt

Differential Erosion of Flat Strata

Stable Platform of N. America Consist of 3 parts Area underlain by Paleozoic strata in east Great Plains region underlain by Mesozoic and Cenozoic strata in the west Atlantic and Gulf coastal plains

Evolution of Columns by Differential Erosion 1. Intersecting joints separate rocks into columns. 2. Weathering and erosion along joints accentuate columns. As weathering and erosion proceed, the cliff retreats. Old columns completely destroyed. New columns being created.

The Atlantic and Gulf Costal Plains Consist of Tertiary and Cretaceous rocks Inclined toward the sea

Appalachian Ridge and Valley Province Anticlines form ridges Synclines form valleys Erosion soon attacks the crests Later stages – tops of folds are eroded away. Hogback ridges are left forming a zigzag pattern.

Erosion of Fault Block Mountains The original dissected upland before faulting consists mostly of valley slopes Faulting is accompanied by accelerated stream erosion Recurrent movement along the fault produce fresh scarps and are dissected by stream erosion.

Basin and Range Province Faulting produces maximum relief, playa lakes may develop. Mountain range is completely dissected. Alluvial fans spread out into the valley. Basins become filled with sediment. Erosion wears down the mountain ranges to small remnants. Alluvial fans merge to form Bajadas.

Landscape from Basaltic Volcanism Lava extruded, blocks drainage. Cinder cones are worn down. Volcanic necks left. Lava flows form sinuous ridges or inverted valleys. Inverted valleys are eroded to mesas and buttes. Volcanic necks and dikes commonly form peaks and isolated ridges.