Recognition of continental scale glaciation occurred
about a century and a half ago and replaced the diluvial hypothesis. Initially,
four major glacial episodes, with interglacials, were proposed but modern
interpretation and oxygen-isotope curves from deep sea sediments suggest many
more alternating cold and warm episodes extending back well over two million
years. On land, the younger glacial episodes obliterated most of the evidence
left by the older ones.
The effects of glaciation, in addition to well-known
eye-catching features like erratic boulders and scratched bedrock surfaces,
resulted in situations of engineering significance which include:
- Worldwide sea level falls or rises, responding to
glacial and interglacial oscillations, which resulted in:
- buried valleys
- complex river terraces along valleys
- dead coral reefs, marine beaches and deltas, now high and dry
- temporary land bridges drowned by high sea levels
- submerged beach ridges and other drowned features on continental shelves
- submarine canyons extending from continental shelves to the deep sea
- Extensive covering of much of the world's land (and sea bed) surface by complex
tills (i.e. morainic material) both from valley glaciers and continental glaciers.
- Vast volumes of granular fluvio-glacial debris issuing from the margins of
continental glaciers and snouts of valley glaciers; on the retreat of the
glaciers these materials covered the till laid down by the glaciers
- Repeated glaciations which built up sandwiches of fluvio-glacial material
overlying true glacial (till) material, perhaps overlying older till material,
all of which became weathered and overlain by alluvial and other deposits of
the interglacial or postglacial warmer climates.
- Overdeepening of valleys and other glaciated terrain with production of
irregular bedrock profiles.
- Numerous lakes of all sizes forming near the glaciated regions, often
containing annual varve laminations (which can be counted like tree rings).
- Enormous volumes of silt carried away by the wind from valleys that
drained the melting glaciers and deposited as loess over vast areas of
northern hemisphere continents.
- Extensive periglacial conditions, i.e. freeze-thaw activity over many,
many summer/winter cycles, significantly disturbing near surface profiles
affected by these conditions (covering about a third of the earth's land
surface at times of maxima) and producing, along with glacial deposits, their
own features, e.g. solifluction debris, cambering, valley bulging, pingos, all
of which have a significant effect on engineering.
- Many tens of metres of isostatic rebound, much still continuing, of the
crust formerly warped downwards by the load of ice sheets thousands of
metres thick .
- Extensive changes to margins and characteristics of hot deserts,
equatorial and monsoonal rainforests and other climatically related