Climate and geomorphology 2

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Climate and geomorphology 2
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Drylands some characteristics
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Low rate of weathering rock is often
exposed Mostly mechanical weathering coarse
debris Slow pedogenesis no well developed soil
profiles
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Patina of different kind, generally known as
rock- or desert varnish is characteristic of dry
environments.
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Mechanical weatheing predominates. Salt
weathering is probably effective
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Granular disintegration of granite in a dry
environment, Panamint Range California.
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Ledges with gypsum in this coastal section shows
that solube salts still exists and is not leached
from the soil
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A combination of mechanical weathering and
surface runoff that washes away the fines from
slopes produce stony pavements and skeletic soils.
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Where fines exists shrinkage and cracking may
occur
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Drainage density is high due to surface runoff.
Streams are ephemeral.
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The upper part of stream channels is often
canyon-like because of the high capacity of flow
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Lower reaches is often characterized by braided
channels due to the loss of stream power and
heavy sediment load.
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Slopes are sensitive to land use changes
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Subsurface flow in pipes is common
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Internal drainage and inland basins are common.
Natural and artificial salisinization of soils.
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Wind is important
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The role of wind depend on the vegetation cover.
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Wind erosion leads to deflation.
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And to transport of sand in desert dunes
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And deposition of loess outside the margins of
deserts
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The Humid tropics
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Dense vegetation, high precipitation and
temperature. Rapid chemical weathering Clayey
soils
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Landscape developed in deeply weathered bedrock,
Kenya Often referred to as multiconvex landscapes
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Saprolite exposed in road cut, Ecuador
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Weathering profile (from Thomas 1994)
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Laterite, Kenya
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As it dry the laterite become very hard and forms
a ferricrete, plinthic acrisol
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Exposure of crusts such as ferricretes are often
an indicator of environmental change, for example
climate change
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Laterite is often used as building brick
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Tropical rivers mostly transport dissolved load
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This is not true for humid tropical mountain
streams.
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Dambos are landforms that characterize the
savanna environments. Are they formed by chemical
denudation ?
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The tors found in many savanna environments
evidence climate change
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As does this landscape from Zimbabwe. This is the
exposed weathering front, formed by deep
weathering in a more humid climate.
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Stone lines found in many tropical soils nmay
also indicate change
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The End