Vocab

Question 1

What is porosity?

Answer 1

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.

Question 2

What are pseudo-bedding planes?

Answer 2

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.

Question 3

What is regolith?

Answer 3

Weathered rock material of all shapes and sizes overlying bedrock. Forms the parent material for soil.

Question 4

What is a resurgent stream?

Answer 4

A stream that emerges from underground, usually at the base of a limestone outcrop.

Question 5

What are rills and gullies?

Answer 5

Fluvial erosion scars on slopes where channels of water have formed and removed soils and regolith. Gullies are larger and deeper than rills.

Question 6

What is a rotational slump/slip?

Answer 6

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).

Question 7

What is salt weathering (crystallisation)?

Answer 7

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.

Question 8

What is scree?

Answer 8

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.

Question 9

What is sheet wash/surface wash?

Answer 9

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.

Question 10

What are slides?

Answer 10

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.

Question 11

What is slope profile or shape?

Answer 11

The slope as seen in cross-section; slope elements include crest, free face, convex, rectilinear, concave and foot-slope sections.

Question 12

What is soil creep (heave)?

Answer 12

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.

Question 13

What is solifluction?

Answer 13

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.

Question 14

What is talus?

Answer 14

The same as scree.

Question 15

What is a tor?

Answer 15

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).

Question 16

What is weathering?

Answer 16

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.

Question 17

What is a flow in geological terms?

Answer 17

A relatively fluid type of mass movement where mud, earth, debris is mobilised after becoming saturated and moves downslope behaving as a liquid.

Question 18

Define free face in geology.

Answer 18

A steep and mainly bare rock face exposed to active weathering and erosion.

Question 19

What is freeze-thaw weathering?

Answer 19

A physical weathering process in which water enters joints in rocks, freezes and expands by approximately 9%; repeated cycles cause rocks to disintegrate.

Question 20

What is frost-shattering?

Answer 20

The result of freeze-thaw weathering.

Question 21

Describe granite.

Answer 21

Coarse-grained, acid intrusive igneous rock, made of crystals of quartz, mica and feldspar; about 400 varieties, with much variation in colour and texture.

Question 22

What is granular disintegration?

Answer 22

A small-scale weathering process in which physical weathering processes attack individual grains, causing them to separate.

Question 23

What is growan?

Answer 23

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.

Question 24

Define hydration in the context of weathering.

Answer 24

Chemical weathering in which whole water molecules are absorbed by rock minerals, leading to expansion and decomposition.

Question 25

What is hydrolysis?

Answer 25

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).

Question 26

What are impermeable rocks?

Answer 26

Rocks which do not allow water to pass through them, either because they lack joints or bedding planes, or because they have no pores.

Question 27

What is insolation weathering?

Answer 27

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.

Question 28

Define intrusive igneous rocks.

Answer 28

Rocks formed from the cooling of molten magma underground, characterized as coarse grained.

Question 29

What are joints in geological terms?

Answer 29

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.

Question 30

What is mass-movement?

Answer 30

A general term for the downslope movement of coherent bodies of weathered material under the influence of gravity; includes heaves, flow, slides, and falls.

Question 31

Describe a mudflow.

Answer 31

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.

Question 32

What is oxidation in the context of weathering?

Answer 32

A chemical weathering process in which oxygen dissolves in rainwater and reacts with certain rock minerals, especially iron, to form oxides and hydroxides.

Question 33

Define permeability.

Answer 33

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).

Question 34

What is physical (mechanical) weathering?

Answer 34

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.

Question 35

What is basal undercutting?

Answer 35

Undercutting at the foot of a slope by an erosive force such as a river or the sea; also known as sapping. ## Footnote It makes the slope above steep and unstable.

Question 36

Define batholith.

Answer 36

Large dome-shaped igneous intrusion, usually made of granite.

Question 37

What are bedding planes?

Answer 37

Dividing lines between the layers (beds) of rock.

Question 38

What is biological weathering?

Answer 38

Bio-physical or bio-chemical weathering caused by biological organisms; either bio-physical (e.g. root action) or bio-chemical (e.g. chelation).

Question 39

What is carbonation?

Answer 39

Chemical weathering process in which dilute carbonic acid converts calcium carbonate in limestone into calcium bicarbonate, which is highly soluble in water.

Question 40

What characterizes Carboniferous limestone?

Answer 40

Hard, crystalline form of limestone of Carboniferous age which usually forms areas of high relief.

Question 41

What is chalk?

Answer 41

White, porous form of limestone; in Britain it is often highly fractured by frost action making it more permeable.

Question 42

Define chelation.

Answer 42

Bio-chemical weathering process in which rainwater passes through rotting vegetation, acquiring an acidic organic extract (chelating agent) capable of combining with metallic substances.

Question 43

What is chemical weathering?

Answer 43

The decomposition of rocks caused by acids dissolved in rainwater reacting with rock minerals; includes carbonation, hydrolysis, hydration, oxidation (and reduction), chelation and solution.

Question 44

What is clay?

Answer 44

Very fine-grained rock that is impermeable, with particles <0.002mm in size, originating from the weathering of rock minerals such as feldspar.

Question 45

What is creep?

Answer 45

The slow downslope movement of soil or other loose surface material due to freezing and thawing, wetting and drying, or heating and cooling cycles.

Question 46

Define debris-flow.

Answer 46

Type of mass movement involving fast flowing materials of a wide range of sizes, lubricated by water or a cushion of compressed air.

Question 47

What does denudation refer to?

Answer 47

The combined effects of weathering, mass-wasting, and erosion in lowering the landscape, possibly forming a peneplain.

Question 48

What is pressure-release?

Answer 48

The jointing and disintegration of underlying rock caused by erosion and removal of overlying rocks.

Question 49

Define escarpment.

Answer 49

An outcrop of tilted rock strata with a steep (scarp) face in one direction and a gentle (dip) slope in the other.

Question 50

What is exfoliation?

Answer 50

Weathering process in which the outer layers of a rock outcrop are broken, split, and peeled-off, often caused by heating and cooling.

Question 51

What are falls in the context of mass movement?

Answer 51

Type of mass movement in which weathered rock material suddenly becomes detached from a rock face and falls freely to the ground.