Environmental Engineering Reference
In-Depth Information
Little Ice Age glacier advances from the mid-fifteenth century to the mid-nineteenth
wrought widespread havoc directly and through their impact on other geophysical
processes, clearly evidenced in oral and documentary history and in the landscape. Their
moraines stand as surviving reminders of previous uncertain times.
Less directly, glacigenic sediments underpin huge tracts of profitable farmland, and
glaciers have, over thousands of y ears, shaped landscapes of high scenic and therefore
tourist value in which - gleaming white and blue in sunlight - they are jewels. Glacier
retreat exposes unstable terrains with large volumes of unconsolidated sediments, bare
rock and new rock basins. Enhanced water and sediment fluxes can be expected from
destabilized slopes, only slowly modified as vegetation colonization and succession
occur. The response of vegetation and timberlines to rising snowlines is 10
2-3
years, so
both will lag behind, and are out of equilibrium with, climate change. New farmland
takes time to develop but alpine scenery could be degraded rapidly by glacier retreat.
variations exploited by plants which often enhance the geomorphology, creating ground
hummocks or
thufur
and string bogs or
muskeg
.
Instability occurs throughout the permafrost environment as the active layer develops
during early summer melt. It accelerates slope movement and turns low-lying and level
ground into a chaotic mire. The water is unable to drain through underlying permafrost
and, for a few weeks, rivers become highly erosive agents of the fluvial environment.
Floating ice is an additional abrasive tool and many valleys become misfits or are
abandoned altogether by surface drainage in normally porous rocks on the return of a
more temperate climate.
CONCLUSION
Glaciation is a regular and predictable Earth surface state and not a climatic freak or
'accident'. It is not merely a by-product of climatic change but also instigates or mitigates
it through ice sheet-ocean-atmosphere coupling. Ice sheet and alpine glacier growth is
strongly influenced by tectonic activity and supercontinental cycles as well as
Milankovich mechanisms (see Chapter 11). Glaciers, in turn, then drive other forms of
glaciotectonic coupling through the rapid alteration of crustal loading by ice sheet growth
and decay, glacial erosion and sediment transfers, and glacio-eustasy. All this endows
glaciers and permafrost with material and geomorphic systems which are not solely
determined by climate but interact with climatic and tectonic processes to set their own
rules.
The environmental influence of glaciers and permafrost extends well beyond their
current geographical distribution. It matters little to human endeavour that Earth may
endure long periods without Ice Ages. The greater part of hominid evolution has occurred
during the Quaternary Ice Age and continues to be profoundly influenced by it. Dramatic
human population explosion and almost all our technological innovation have occurred in
just 10 ka of the current (Flandrian) interglacial cycle. We need to be as responsive to
Earth's icehouse as to its greenhouse modes.
