Landforms and Rock Structure

Transcription

1 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

2 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 Figure 17.1, p. 577

3 Landforms and Rock Structure principal rock structures and associated landforms Figure 17.2, p. 577

4 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

5 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

6 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

7 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

8 Landforms of Horizontal Strata and Coastal Plains coastal plains exhibit alternating belts of cuestas and lowlands Figure 17.8, p. 583

9 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

10 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

11 Landforms Developed on Other Land-Mass Types active normal faulting produces a sharp surface break called a fault scarp erosion quickly modifies a fault scarp, but because the fault plane extends hundreds of meters down into the bedrock a subsequent stream often marks the zone of weakness along a fault plane Figure 17.16, p. 586

12 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

13 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

14 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

15 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