cirrostratus, and cirrocumulus. Cirrus clouds are formed from individual, detached
elements that appear white and fibrous. The word “delicate” is frequently applied
to this type. Cirrostratus clouds frequently cover the entire sky and seem to form a
“veil” high in the sky. These first two types are formed at elevations where there is
slowly rising air or into air that has acquired moisture. They are sometimes difficult
to identify from each other because both cirrocumulus and cirrostratus clouds fre-
quently change into each other. The cloud decks made by stratus and cirrostratus
clouds can be geographically extensive but are thin and allow considerable sunlight
to penetrate them. They are often omens of surface weather disturbances following a
day or more behind. Cirrocumulus clouds appear as small units organized as patches
in the sky. They denote a faster rise of air than in cirrus or cirrostratus and their indi-
vidual cloud elements are smaller than those in altocumulus.
The final cloud family is composed of clouds with vertical development. The
two principal types are cumulus and cumulonimbus clouds. These clouds develop
in air that is unstable and rising quickly. Cumulus clouds are the smaller of the
two. Their bases are usually at modest heights from the ground and define the low-
est level at which the rising air has become saturated. They consist of large, puffy
elements that have sharply defined edges sometimes likened to cauliflowers. These
clouds are the result of convection caused by surface heating and are common
sights in summer. Cumulonimbus form from the towering and merging of individ-
ual cumulus clouds.They are also known asthunderstormsand are clouds made
by the rapid rise of air to very great heights up to and sometimes punching through
the tropopause to enter the lower stratosphere. These clouds are the focus for tre-
mendous amounts of latent heat exchange and a variety of severe weather effects
including immense amounts of rainfall.
Coastal Erosion and Deposition
Coastlines are fascinating in mass and energy terms because it is here thatatmos-
phere, lithosphere, biosphere, and hydrosphere vigorously interact. They are also
of great importance to humans because of our historic attraction to moderate cli-
mates, ocean trade, and fishing.
Water can erode shoreline material in several ways. The most significant
method of erosion is by the tremendous hydraulic force provided by waves. Even
modest waves can focus enough energy to break apart rock material and transport
the loose remains. At the extreme, some coastlines are subject to large tsunamis
generated by earthquakes. These are rare but can accomplish considerable erosion.
The chemical action of water is considerable and able to break down rock by
Coastal Erosion and Deposition 67