Landforms Why does the land look like it does? 1. Controlled by water 2. Controlled by the rocks
Landforms Made by Running Water Stream erosion The evolution of a river system Entrenched meanders Fluvial Processes in Arid Climates
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Erosion and landcover Land use and cover has a big impact on rates of erosion Figure 16.3, p. 548
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High rates of erosion when vegetative cover is sparse
Higher rates of erosion when vegetative cover is gone.
Boulders scour out potholes in the rock
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The gradient of the stream evolves into a gentle slope
Initially the gradient is steep with water falls
The stream quickly cuts deeply into the rock because the current is so fast
Tributaries attack the whole mountain; the main trunk widens
The river continues to widen as it erodes the sides and fills the floodplain with sediment
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Landforms and Rock Structure Rock Structure as a Landform Control Landforms of Horizontal Strata and Coastal Plains Landforms of Warped Rock Layers Landforms Developed on Other Land-Mass Types
Landforms and Rock Structure rocks differ in their resistance to denudation more resistant rock tends to form uplands and ridges while weaker rock forms lowlands and valleys rock layers can be tilted, folded and fractured by tectonic forces
Landforms and Rock Structure principal rock structures and associated landforms Figure 17.2, p. 577
Landforms and Rock Structure the tilt and orientation of rock layers and fractures are described by their strike and dip strike - orientation of the rock plane with respect to compass direction dip - angle between rock plane and horizontal plane Figure 17.3, p. 578
Landforms of Horizontal Strata and Coastal Plains plateaus, mesas, and buttes are landforms of flat-lying erosion resistant strata in arid regions slopes in these regions form stair-step sequences of vertical risers of resistant rock with sloping treads of weaker rock Figure 17.1, p. 577
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Landforms of Horizontal Strata and Coastal Plains Dendritic: uniform surface Trellis: inclined layers of sedimentary rock Radial: around a hill drainage networks have characteristic patterns
Landforms Developed on Other Land-Mass Types Erosion of shield volcanoes: (a) (a) newly formed dome with central depression (b) early stage of erosion with deeply eroded valley heads (b) (c) advanced erosion stage with steep slopes and mountainous relief (c) Figure 17.24, p. 593
Mauna Kea: Shield Volcano
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Landforms of Horizontal Strata and Coastal Plains coastal plains are found along passive continental margins consequent streams flow to the sea across the belts, fed by subsequent streams that drain the cuestas and lowlands Figure 17.7, p. 582
Landforms of Warped Rock Layers a sedimentary dome, a circular or oval structure in which strata have been forced upward into a domed shape igneous intrusions at great depth are responsible for some of these uplifts erosion features: strata are first removed from the summit region of the dome, exposing older strata beneath (eroded edges of steeply dipping strata form sharp-crested saw-tooth ridges called hogbacks) Figure 17.9, p. 583
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Continental Interiors Structural basin Circular or oval depression of stratified rock Structural dome Circular or oval uplift of stratified rock Erosion leads to circular pattern 52
Continental Interiors Domes and basins of North America 53
Continental Interiors Black hills of South Dakota Oblong dome 54
Black Hills Uplift
The Michigan Basin
Old folded and faulted
Fig. 23.15. Differential erosion in folded rocks
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Landforms of Warped Rock Layers fold belts create a ridge-and-valley landscape of alternating resistant rock ridges and weak-rock valleys these linear features lead to the formation of a trellis drainage pattern Figure 17.13, p. 585
Northern Rocky Mountains Young folded and faulted
Fig. 23.18d. Faceted spurs in block faulted mountains Wasatch Mountains, UT
Landforms Developed on Other Land-Mass Types slate and marble are weak metamorphic rocks that underlie valleys schist, gneiss, and quartzite are more resistant and underlie uplands and ridges Figure 17.18, p. 587
Landforms Developed on Other Land-Mass Types huge plutons of intrusive igneous rock are formed deep below the Earth s surface some are eventually uncovered by erosion and appear at the surface batholiths are typically composed of resistant rock (eroded into hilly or mountainous uplands) a monadnock is an isolated projection of intrusive igneous rock surrounded by an eroded plain Figure 17.20, p. 588
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Sedimentary layers may extend for many miles
Landforms Developed on Other Land-Mass Types eroded volcanoes develop a radial drainage pattern of streams leading away from the summit at the last stage of erosion, all that remains is a volcanic neck with radial dikes Figure 17.21, p. 589
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Devil s Tower; a volcanic neck, a feeder pipe
Shiprock, New Mexico; a volcanic neck
Rhumski, Cameroon; a volcanic neck