Environmental Engineering Reference
In-Depth Information
NEW ZEALAND: SOUTHERN ALPS
The Southern Alps afford an outstanding example of the relationship between
contemporary tectonics and young mountains, despite their smaller scale. New Zealand
occupies a microcontinental plate astride convergent Indo-Australian and Pacific plates.
The Pacific plate is subducting beneath North Island along the Kermadec- Hikurangi
trench. This generates B-subduction volcanic activity centred on the andesitic volcanoes
of Mount Egmont (2518 m) and Ruapehu (2796 m), volcanic springs around the Lake
Taupo caldera and the Rotorua
ignimbrite
plateau. In contrast, the Pacific plate takes
South Island
over
subducting Indo-Australian plate. Both zones are connected by the
transform Alpine Fault which has been the focus for uplift of the Southern Alps for the
past 5 Ma (Figure 25.7). Mesozoic oceanic sediments have been thrust and
metamorphosed against Palaeozoic granite batholiths to form a steady-state cordillera 2-3
km high and 750 km long. Peaks reach 2·5-3·8 km, including New Zealand's highest,
Mount Cook (3764 m), in its central 240 km-long core. Rapid horizontal plate movement
of more than 45 mm a
−1
is consumed mostly in crustal shortening, creating an
asymmetrical range 100-150 km wide which rises dramatically from the west coast
before falling a further 25-70 km across the eastern coastal plain. Among Earth's highest
uplift rates at 2 cm a
−1
, this harnesses vigorous westerly air streams to trigger intense
Quaternary fluvial and glacial erosion. Some mountain blocks may have been elevated 1
km - the height of Britain's highest mountains today - in just 250,000 years. The
Southern Alps enjoy some of Earth's most dramatic dissection and erosion rates, and the
size, character and latitude of modern New Zealand make it a reasonable analogue of
volcano-tectonic Britain during the Lower Palaeozoic.
MOUNTAIN METEOROLOGY AND CLIMATE
Mountains cover 20 per cent of Earth's terrestrial surface, yet mountain weather and
climate often receive scant attention beyond their role in generating major disturbances in
planetary atmospheric waves and the phenomena of valley winds. Comprehensive
mountain meteorological data are limited by mountain remoteness, low population
density and instrumental failure due to the harsh climate. Beyond a systematic decline in
temperature with altitude and a parallel tendency towards higher relative humidity, cloud
cover and precipitation, mountain
topoclimates
provide a mosaic of rapid spatial and
seasonal change. They are difficult to map accurately and many parameters are
susceptible to significant feedback from the geomorphic and vegetation surfaces which
they promote. However, we must grasp their climatic character to understand the true
nature of mountain environments.
ENVIRONMENTAL PROBLEMS IN MOUNTAIN AREAS
applications
Mountain environments are naturally prone to catastrophic geophysical processes -
landslides, debris flows, earthquakes, volcanic eruptions, glacier lake bursts and flash
floods. Quite simply, that is how their landsystems evolve, and any one may trigger
others
There
are
also
biometeorological
hazards
to
high altitude
living
Anoxia
