Environmental Engineering Reference
In-Depth Information
Nivation
The erosion of surface depressions by the combined processes of rock
weathering and mass wasting associated with the growth and decay of snowpack.
Nordenskjöld line
The limit of the Arctic and Antarctic as defined by both the
temperature of the warmest month and the temperature of the coldest month.
Normal stress
The portion of rock or soil strength dependent on the anchoring effect of
the mass of a particle or intact block, normal (at right-angles) to a surface on which it
rests; this is at a maximum if the surface is horizontal but diminishes as slope angle
increases.
Nuée ardente
An incandescent (fiery) cloud of
ash
and volcanic gas developing as near-
surface
pyroclastic
gravity flow after volcanic eruption, capable of destroying
anything in its path.
Nunatak
An isolated mountain or hill protruding through, and completely surrounded by,
glacier ice.
Obligate symbiotic relationships
Relationships which are restricted to specified
conditions only.
Obliquity of the ecliptic
The tilt of Earth's axis of rotation relative to the plane of its
orbit. It varies between 21·8° and 24·4° over a period of about 40,000 years.
Occupational fire
A fire started by humans in order to manage an
ecosystem
for
economic gain (e.g. grazing, land clearance or herding wild animals).
Offshore
A zone of deeper water lying on the inner margins of the continental shelf,
beyond the
nearshore
zone.
Ooze
Fine-grained, marine sediment comprised of more than 30 per cent skeletal remains
of
pelagic
organisms and clay minerals.
Open systems
Systems which are characterized by the exchange of both matter and
energy with their surroundings. The majority of natural systems are open.
Ophiolite
A sliver of oceanic crust caught up in an
accretionary prism
and found out of
place in a subsequent
orogen
.
Organismic community
The concept which regards the
plant community
as a 'super-
organism', with properties not present in its individual constituent organisms.
Orogen
A linear continental mountain range elevated mechanically or thermally by plate
collision, crustal shortening and uplift.
Orogenesis
The formative processes of an orogen.
Oroshi
A cold-air drainage current blowing from the mountains of central Japan.
Orthogonal
Said of a system with right-angle relationships between its components.
Outlet glacier
A steep, fast-flowing
glacier
discharging large ice volumes from inland
portions of
ice sheets
through a confining rock-walled channel.
Output
The flow of energy and matter out of a system.
Outwash plain
An extensive land surface covered by glaciofluvial sediments and
braided meltwater streams released from a glacier terminus, especially in unconfined
piedmont zones.
Overbank discharge
That portion of stream discharge not confined to the channel during
a flood.
Overburden pressure
A compressive stress exerted on Earth material by the mass of
overlying rock, soil, water or ice.
Overland flow
Non-channelled surface water flow where precipitation intensity exceeds
infiltration capacity, taking two forms:
Horton overland flow
develops as
sheet flow
on