Rock Structure as a Landform Control

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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.
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Rock Structure as a Landform Control
Sandstone Butte, Sedona, Arizona
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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.
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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.
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Arid Regions
In arid climates, distinctive erosional landforms
develop in horizontal strata
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Arid Regions
Buttes in Tunisian Desert Ca. 1990s Tatawin,
Tunisia.
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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.
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Coastal Plains
Development of a broad coastal plain. (a) Early
stage - plain recently emerged. (b) Advanced
stage - cuestas and lowlands developed.
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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.
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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.
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Sedimentary Domes
A sandstone dome is orange in the early morning
light, Valley of Fire State Park, Nevada
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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.
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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.
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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.
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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.
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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.
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Fault Scarps
Red Canyon Fault Line.
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Exposed Batholiths and Monadnocks
Batholiths, large igneous intrusions, may
eventually become exposed at the surface as
overlying rocks are eroded away.
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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.
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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.
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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.
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Eroded Volcanoes
Mount Bromo, an eroded volcanic cone in Bali,
Indonesia.
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