256 Green Chemistry, 2nd ed
Along with weather and climate, human activities can influence the likelihood and
destructiveness of landslides. Roads and structures constructed on sloping land can
weaken the integrity of earthen material or add mass to it, increasing its tendency to slide.
In some cases, strong root structures of trees and brush anchor sloping land in place.
However, some plant roots destabilize and add mass to soil, increase the accumulation
of water underground, and cause earth to slide. Fortunately, predicting a tendency for
landslides to occur is relatively straightforward based upon the nature and slope of
geological strata, climate conditions, and observations of evidence of a tendency toward
landslides, such as movement of earth and evidence of cracked foundations in buildings
built on slopes. In some cases remedial actions may be taken, but more important are the
indications that structures should not be built on slide-susceptible slopes.
Less spectacular than landslides is creep characterized by a slow, gradual movement
of earth. Creep is especially common in areas where the upper layers of earth undergo
freeze/thaw cycles. A special challenge is permafrost which occurs in northern
Scandinavia, Siberia, and Alaska. Permafrost refers to a condition in which ground at
a certain depth never thaws, and thawing occurs only on a relatively thin surface layer.
Structures built on permafrost may end up on a pool of water-saturated muck resting on
a mixture of frozen ice and soil. One of the greater challenges posed by permafrost in
recent times has been the construction of the Trans-Alaska pipeline in Alaska.
Expansive clays that alternately expand and contract when saturated with water, then
become dried out, can cause enormous damage to structures, making the construction
of basements virtually impossible in some areas. Sinkholes occur in areas where rock
formations are dissolved by chemical action of water (particularly dissolved carbon
dioxide acting on limestone). Earth can fall into a cavity generated by this phenomenon
causing huge holes in the ground that can swallow several houses at a time.
10.3. Water in and on the Geosphere
The geosphere is the repository of virtually all the world’s fresh water. As shown in
Figure 10.1, this water may be in underground aquifers as groundwater; on the surface
as streams, rivers, lakes and impoundments; or as deposits of ice (glaciers) resting on
Earth’s surface. Water collected by the geosphere constitutes virtually all Earth’s fresh
water resources. This water is susceptible to pollution which in extreme cases can render
the water sources virtually useless. One of the greater water pollution problems is when
water in underground aquifers becomes contaminated with hazardous waste material
improperly discarded in the geosphere.
Water commonly moves on the geosphere in streams or rivers consisting of channels
through which water flows. Rivers collect water from drainage basins or watersheds.
In order to protect water quality in rivers, pollution and pollution-causing agricultural
practices in drainage basins must be avoided. Rivers continually erode the geosphere
over which they flow and leave deposits of sediments. Over time, a river will erode earth
away and create valleys. An undisturbed river continually cuts curving patterns known
as meanders in a river valley. The flat area of a valley formed by erosion and sediment
deposition in the valley and susceptible to periodic flooding is the river’s floodplain.