Geoscience Reference
In-Depth Information
Hydrological sequence
The topographic sequence of
soils, from ridge crest to adjoining valley bottom, which
reflects the changing soil-water regimes downslope.
Hydrolysis
A form of chemical weathering in which the
H
+
and OH
-
ions of water react with a mineral, with
consequent loss of strength.
Hydrometeorology
The study of the atmospheric part of
the hydrological cycle and the association between
precipitation, evapotranspiration and the
drainage basin
.
Hydrophobic
Icehouse
An uncommon condition in which Earth's
average global temperature may be nearer to that
predicted by radiation laws by virtue of the presence and
autocatalytic
consequences of large ice sheets and frozen
ocean surfaces.
Ice-wedge polygons
Polygon-shaped surface markings
in periglacial landscapes whose outlines are marked by ice
wedges within the underlying
permafrost
.
Igneous
Of molten, partly molten or magmatic nature
and origin.
Ignimbrite
The cooled and lithified product of a volcanic
ash flow
, also known as an
ash-flow tuff
.
Inceptisol
A soil order (USDA classification) charac-
terized by the alteration or removal of minerals other than
carbonates or amorphous silica.
Incised meanders
The entrenched bedrock channels of
old river meanders after
rejuvenation
.
Incision
The erosion of a narrow, bedrock river channel
by vigorous fluvial downcutting.
Indentation tectonics
Crustal deformation caused by
the penetration of one continental plate by another and
involving head-on compression, lateral extension and
rotation in the affected crust.
Individualistic communities
The concept that
plant
communities
represent an assemblage of plant species with
overlapping environmental requirements which arise
because of random propagule availability.
Infiltration
The process by which water enters a soil
through pores or cracks at the surface from precipitation,
depression storage
or
overland flow
.
Infiltration capacity
The maximum rate at which water
may infiltrate soil or rock.
Infiltration rate
The rate at which water added to the
surface can enter the soil.
Information theoretic index
A measure of ecological
diversity derived from the theory of information (e.g. the
Shannon index).
Inhibition model
The model of succession in which
changes in floristic composition are prevented until an
established species dies out.
Input
The flow of energy and matter into a system.
Inselberg
A residual hill in massive, resistant rock which
has survived the
weathering
and stripping of adjacent
rock mass through its superior strength.
Inshore
The shallow-water coastal zone below the low-
water mark in which waves
shoal
.
Insolation
A contraction of
in
coming
sol
ar radi
ation
.It
refers to the short-wave part of the solar energy input.
Insolation weathering
A form of mechanical weathering
in which rock-mass disintegration is attributed to
diurnal thermal expansion and contraction; this form of
A soil structure or soil constituent which
repels water.
Hydrophyte
A plant adapted to growth in wet or
waterlogged conditions.
Hydrosere
The sequence of
plant communities
which,
successively, occupy a silting-up freshwater lake.
Hydrosphere
Earth's outer, liquid envelope, concentra-
ted almost entirely within the oceans and its liquid,
gaseous and solid derivatives on the land surface and in
the lower atmosphere.
Hydrothermal alteration
The chemical
weathering
of
minerals induced by exposure to a different thermal and
moisture environment from that in which they formed.
Hydrothermal circulation
Sea-water circulation through
mid-ocean ridges, entering through extension faults and
pumped back out through axial vents, and its associated
hydrothermal plume
of new minerals formed by chemical
reactions between the heated water, oceanic crust and
magma.
Hydrothermal plume
The efflux of sea water and dis-
solved minerals from axial vents in mid-ocean ridges.
Hygroscopic
Said of water retained by or attracted to soil
or dust particles and not evaporated at ordinary
temperatures and pressures.
Hypsithermal
The 'climatic optimum' or period of
highest global mean annual temperature, between 8,000
and 5,000 years ago, during the
Holocene
or current
temperate stage.
Ice lens
A discrete, sub-surface layer in permafrost
composed solely or mostly of
ground ice
.
Ice sheet
A large, subcontinental- or continental-scale
glacier of tabular shape which buries all or most of the
land surface.
Ice shelf
The floating portion of the margins of an ice
sheet which, owing to the absence of basal shear stress,
spreads and thins over the sea surface.
Ice wedge
A mass of
ground ice
forming a vertical wedge
in desiccation/contraction cracks.
Iceberg
A block of ice which has become detached from
a floating glacier or
ice shelf
.
Icefall
A steep, rapidly flowing and heavily crevassed
glacier segment moving by
extending
or
surging
flow.
