Vocab Flashcards
What is porosity?
The volume of pore spaces within a rock or soil; expressed as the ratio of the volume of pore spaces to the total volume of the material. It varies from 25 - 35% for alluvial gravels, to 0.001% for slate.
What are pseudo-bedding planes?
Structures in igneous rocks which resemble the bedding planes found in sedimentary rocks; usually caused by expansion of the rock on pressure release, resulting from erosion of the overlying rocks.
What is regolith?
Weathered rock material of all shapes and sizes overlying bedrock. Forms the parent material for soil.
What is a resurgent stream?
A stream that emerges from underground, usually at the base of a limestone outcrop.
What are rills and gullies?
Fluvial erosion scars on slopes where channels of water have formed and removed soils and regolith. Gullies are larger and deeper than rills.
What is a rotational slump/slip?
A slide type of mass-movement in which masses of surface material move along a curved (semi-circular) plane; common on cliffs in which permeable (e.g. shale) material overlies impermeable (e.g. clay).
What is salt weathering (crystallisation)?
A physical weathering process in which water containing salts in solution enters the joints or pores of a rock; when the water evaporates, salt crystals can grow and break the rock apart; occurs commonly on coasts and in hot deserts.
What is scree?
A sloping accumulation of angular rock fragments below a cliff or rock face (free face) produced largely by weathering and subsequent rock falls; also called talus.
What is sheet wash/surface wash?
A type of fluvial erosion in which surface debris, such as gravel, sand, silt and clay is moved downslope by overland flow. It is initiated by rain-splash impact, then the loosened debris is moved downslope by water flowing over the surface.
What are slides?
A type of mass movement in which a coherent mass of rock/regolith moves downslope along a slip plane, initially as a solid block, but may subsequently break up.
What is slope profile or shape?
The slope as seen in cross-section; slope elements include crest, free face, convex, rectilinear, concave and foot-slope sections.
What is soil creep (heave)?
A type of mass-movement in which cycles of freezing + thawing, heating + cooling, wetting + drying cause surface materials to rise and fall in a downslope zig-zag motion.
What is solifluction?
A type of mass-movement in which surface material which has been frozen during the winter thaws, becomes plastic, and flows very slowly over the frozen subsurface in periglacial regions.
What is talus?
The same as scree.
What is a tor?
A rocky outcrop, often several metres high, usually made of granite or sandstone. Large blocks of rock, in situ, are separated by distinct vertical joints and horizontal bedding planes (pseudo-bedding plane if granite).
What is weathering?
The disintegration and/or decomposition of rocks in situ creating a layer of waste rock (regolith). Weathering can be chemical or physical and is often aided by biological factors such as plant roots.
What is a flow in geological terms?
A relatively fluid type of mass movement where mud, earth, debris is mobilised after becoming saturated and moves downslope behaving as a liquid.
Define free face in geology.
A steep and mainly bare rock face exposed to active weathering and erosion.
What is freeze-thaw weathering?
A physical weathering process in which water enters joints in rocks, freezes and expands by approximately 9%; repeated cycles cause rocks to disintegrate.
What is frost-shattering?
The result of freeze-thaw weathering.
Describe granite.
Coarse-grained, acid intrusive igneous rock, made of crystals of quartz, mica and feldspar; about 400 varieties, with much variation in colour and texture.
What is granular disintegration?
A small-scale weathering process in which physical weathering processes attack individual grains, causing them to separate.
What is growan?
An accumulated mass of sandy fragments of weathered granite derived from chemical weathering in Dartmoor, primarily quartz grains left behind after hydrolysis of feldspar and mica.
Define hydration in the context of weathering.
Chemical weathering in which whole water molecules are absorbed by rock minerals, leading to expansion and decomposition.
What is hydrolysis?
A chemical weathering process in which water reacts chemically with certain types of rock minerals (e.g. feldspar) to produce insoluble precipitates (usually clays) and insoluble residue (usually sand).
What are impermeable rocks?
Rocks which do not allow water to pass through them, either because they lack joints or bedding planes, or because they have no pores.
What is insolation weathering?
A physical weathering process caused by the alternate heating of rocks by the sun causing expansion during the day, and cooling at night, causing contraction.
Define intrusive igneous rocks.
Rocks formed from the cooling of molten magma underground, characterized as coarse grained.
What are joints in geological terms?
Cracks or partings within a mass of rock caused by stresses such as contraction on cooling, shrinkage on drying out, or the release of overlying pressure.
What is mass-movement?
A general term for the downslope movement of coherent bodies of weathered material under the influence of gravity; includes heaves, flow, slides, and falls.
Describe a mudflow.
A type of mass-movement in which a mass of weathered rock material, including a high proportion of clay liquefies, perhaps after heavy rain, and flows downhill.
What is oxidation in the context of weathering?
A chemical weathering process in which oxygen dissolves in rainwater and reacts with certain rock minerals, especially iron, to form oxides and hydroxides.
Define permeability.
The rate at which water is able to pass through a rock, ranging from totally impermeable (e.g. saturated clays) to highly permeable (e.g. weathered limestones).
What is physical (mechanical) weathering?
The disintegration of rock into angular pieces as a result of freeze-thaw, insolation weathering, salt crystallisation, pressure release, wetting & drying processes, and the organic action of plant roots.
What is basal undercutting?
Undercutting at the foot of a slope by an erosive force such as a river or the sea; also known as sapping.
It makes the slope above steep and unstable.
Define batholith.
Large dome-shaped igneous intrusion, usually made of granite.
What are bedding planes?
Dividing lines between the layers (beds) of rock.
What is biological weathering?
Bio-physical or bio-chemical weathering caused by biological organisms; either bio-physical (e.g. root action) or bio-chemical (e.g. chelation).
What is carbonation?
Chemical weathering process in which dilute carbonic acid converts calcium carbonate in limestone into calcium bicarbonate, which is highly soluble in water.
What characterizes Carboniferous limestone?
Hard, crystalline form of limestone of Carboniferous age which usually forms areas of high relief.
What is chalk?
White, porous form of limestone; in Britain it is often highly fractured by frost action making it more permeable.
Define chelation.
Bio-chemical weathering process in which rainwater passes through rotting vegetation, acquiring an acidic organic extract (chelating agent) capable of combining with metallic substances.
What is chemical weathering?
The decomposition of rocks caused by acids dissolved in rainwater reacting with rock minerals; includes carbonation, hydrolysis, hydration, oxidation (and reduction), chelation and solution.
What is clay?
Very fine-grained rock that is impermeable, with particles <0.002mm in size, originating from the weathering of rock minerals such as feldspar.
What is creep?
The slow downslope movement of soil or other loose surface material due to freezing and thawing, wetting and drying, or heating and cooling cycles.
Define debris-flow.
Type of mass movement involving fast flowing materials of a wide range of sizes, lubricated by water or a cushion of compressed air.
What does denudation refer to?
The combined effects of weathering, mass-wasting, and erosion in lowering the landscape, possibly forming a peneplain.
What is pressure-release?
The jointing and disintegration of underlying rock caused by erosion and removal of overlying rocks.
Define escarpment.
An outcrop of tilted rock strata with a steep (scarp) face in one direction and a gentle (dip) slope in the other.
What is exfoliation?
Weathering process in which the outer layers of a rock outcrop are broken, split, and peeled-off, often caused by heating and cooling.
What are falls in the context of mass movement?
Type of mass movement in which weathered rock material suddenly becomes detached from a rock face and falls freely to the ground.
