Page 284 - Ultimate Visual Dictionary (DK)

GEOLOGY, GEOGRAPHY, AND METEOROLOGY

Weathering and FORMATION OF A HAMADA (ROCK PAVEMENT)

Wind blows away Larger particles
aggregate
small particles
erosion Hamada
forms
WEATHERING IS THE BREAKING DOWN of rocks on the Earth’s surface.
There are two main types: physical (or mechanical) and chemical.
Physical weathering may be caused by temperature changes, such as
freezing and thawing, or by abrasion from material carried by winds, FIRST SECOND FINAL
rivers, or glaciers. Rocks may also be broken down by the actions of STAGE STAGE STAGE
animals and plants, such as the burrowing of animals and the growth
of roots. Chemical weathering causes rocks to decompose by changing
FEATURES OF WEATHERING
their chemical composition—for example, rainwater may dissolve AND EROSION
certain minerals in a rock. Erosion is the wearing away and removal of
land surfaces by water, wind, or ice. It is greatest in areas of little or no
Mesa (flat-topped plateau)
surface vegetation, such as deserts, where sand dunes may form.
FEATURES PRODUCED BY WIND ACTION

Wind-blown Mushroom- Canyon
sand shaped rock
Zeugen
Neck
Joint
Rock base eroded by
wind-blown sand
Hard rock
ROCK PEDESTAL
Soft rock
Wind-blown Widened Soft Wind-blown Shelf formed
sand joint rock sand of hard rock
Furrow
Hard Talus (scree)
rock
Hard rock Alluvial fan
(alluvial cone)
Soft rock eroded by
wind-blown sand Bahada (gentle
slope covered with
ZEUGEN YARDANG
loose rock)
Bolson (alluvium-
filled basin)
EXAMPLES OF PHYSICAL WEATHERING PROCESSES Talus (scree) Joint widened
by frozen water
Joint expands and contracts Trunk
Heated rock surface due to temperature changes Crack widened
expands Exfoliation by tree root
dome
Block of
fallen
Flaking rock
rock
Fallen
debris

EXFOLIATION BLOCK DISINTEGRATION FROST WEDGING TREE ROOT ACTION
(ONION-SKIN WEATHERING)
282