Geoscience Reference
In-Depth Information
a catastrophic collapse of the western British ice sheet
during deglaciation. It is thought that rising sea level
flooded the northern Irish Sea basin faster than ice retreat,
turning the ice margin into a floating shelf (see
Figure
calving and then to ice sheet surging as its frontal support
collapsed. Drumlin fields in neighbouring low-lying parts
of Ireland, northern England and north Wales may be
indicative of surging glacier behaviour. This would have
reactivated terrestrial ice flow, transferring the zone of
deformation into the sediment body in the manner
required for streamlined bedforms.
PERMAFROST
Permafrost
is defined as a thermal condition in which the
temperature of the soil or superficial deposit remains
continuously below 0
C for at least two years, although
much has been frozen for thousands of years (Brown and
Pewe 1973). Permafrost becomes thinner and patchier in
distribution moving away from the poles, and is divided
Some investigators further subdivide the discontinuous
zone into three, i.e. widespread (
50 per cent), sporadic
Glacier resources and hazards
HUMAN IMPACT
Whether Earth reverts to a 'scheduled' icehouse phase in the near geological future or maintains the greenhouse
trend, human societies will monitor the growth, decay and changing behaviour of glaciers and ice sheets. They convey
mixed blessings of resource or resource potential inseparable from glacier hazard and therefore neither their growth
nor their decay can be wholly beneficial to us. At its simplest, glacier resources relate to the direct consumption of
ice itself. Nature's refrigerator has long been used in glaciated regions for food preservation and cooling - sometimes
even within glacier cavities!
Ice is used more obviously and extensively in its melted state for irrigation and for hydro-electric power generation.
As Earth's largest store of fresh water, its potable and irrigation appeal is inevitable but supplies are restricted
geographically and seasonally in the absence of storage schemes. The feasibility of towing Antarctic icebergs to the
Middle East has been explored, given the high cost of alternative desalinization strategies, but not developed. Glacier
meltwater is a major global source of hydro-electricity generation but is released in high spring and early summer
discharges which still require considerable reservoir storage. Jökulhlaupurdemonstrate that it does not always come
in manageable quantities.
Although meltwater supply is highly seasonal and out of phase with demand, storage as glacier ice retains more
catchment water equivalence than occurs in entirely rain-driven regimes, where mountain run-off is rapidly evacuated
from the basin. This is sensitive to change now that glaciers are generally in retreat, with Norway and New Zealand
among the few regions experiencing glacier advance due to increased precipitation. Forecast global warming will
initially increase summer meltwater supply but glacier retreat leads eventually to sustained reduction. This illustrates
one of two worst-case scenarios. It is likely that alpine glaciers will largely disappear this century, whereas Little Ice
Age glacier advances from the fifteenth century to the nineteenth wrought widespread havoc. Farmland, farms and
villages and marginal lakes were bulldozed in their path and through their impact on other geophysical processes
such as landsliding. All is evidenced in oral and documentary history and in the landscape their moraines stand as
reminders of historically uncertain times.
Glacigenic sediments underpin huge tracts of profitable farmland in northern mid-latitudes, and glaciers have, over
thousands of years, shaped landscapes of high scenic and therefore tourist value in which - glistening white and
blue in sunlight - they are the 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. Vegetation and rising timberlines both
lag behind retreat, out of equilibrium with climate change. New farmland takes time to develop and alpine scenery
will be degraded rapidly by glacier retreat (see p.710).
