Heavens & Earth Chapter 8

"A" horizon

The uppermost soil horizon that is usually rich in organic matter.

"B" horizon

Usually a bright colored soil horizon (yellow-brown-orange-red) found below the A horizon. Sometimes called the "subsoil." A place where leached materials often accumulate.

"C" horizon

Found below the B soil horizon. It is often the same color as the unweathered bedrock and will often contain pieces of the unweathered bedrock within it.

"E" horizon

This horizon is not always present, but when it is it lies below the A/O horizons and above the B horizon. It will be extensively leached and contain minerals.

"O" horizon

A soil horizon with a considerable amount of organic material, typically found at or near the surface.

Abrasion

A process of mechanical or physical weathering where a rock or particle is ground against another rock or particle.

Cavitation

A very powerful mechanical weathering process that happens when vacuum bubbles implode, causing a "sledgehammer-like" effect on a solid material.

Chemical weathering

A process that occurs when rocks are dissolved by various solutions or groundwater.

Debris avalanche

Loose material that can consist of rock, mud, ice, and other debris that tumbles down a slope rapidly.

Debris flow

A loose collection of debris that flows down a stream bed or valley. Similar to a mudflow, but it doesn't contain as much fluid.

Density current

A subaqueous flow of concentrated mud or sand that flows quickly along the bottom of a body of water.

Differential weathering

When one type of rock or substance weathers faster than another.

Earth flow

Occurs when a steep slope, typically consisting of soil, becomes saturated with water and then begins to flow relatively slowly downslope. Significantly slower than a mudflow.

Erosion

The process where rock and/or soil material is picked up and transported to another location.

Frost heaving

When water freezes it expands. If underground, the expanding ice can lift objects like roads, sidewalks, and buildings.

Frost wedging

When water freezes it expands. If the frozen water is in the crack of a rock, it can sometimes apply enough force to further break the rock apart. It is a mechanical or physical weathering process.

Groundwater sapping

A physical or mechanical weathering process by which groundwater flowing out of a cliff face can apply pressure from the inside of the cliff face outward, causing pieces of rock to splay off.

Humus

The part of the soil consisting of organic matter.

Hydraulic action

A physical/mechanical weathering process caused by the force of rapidly flowing water.

Isostatic rebound

Expansion that results after removing a very heavy object which caused compression. For example, a thick glacier might compress a landscape, and when it melts expansion of the underlying rock will occur.

Landslide

A generic term used to describe many different types of mass wasting processes whereby large amounts of material move down a slope quickly.

Loam

Soil composed of sand (40%), silt (40%), and clay (20%). These are often ideal soil types.

Mass wasting

A generic term used to describe any large amount of material that moves down a slope, either quickly or slowly, under the force of gravity.

Mechanical weathering

Processes that disintegrate rock via physical means rather than by chemical means.

Mudflow

A rapid flow process whereby mud flows down a river valley. Typically the mud has a consistency close to wet cement, often with less than 50% water.

Permafrost

Soil in polar regions that remains frozen year round. During the summer the surface layer can melt, but deeper layers remain frozen.

Relief

The vertical distance from the highest point in a landscape to the lowest point.

Rock avalanche

Rock that tumbles quickly down a hillside.

Rock creep

Rock that moves slowly down a hillslope under the influence of gravity.

Rockfall

Rock that freefalls from a cliff face. The broken material usually accumulates at the bottom of the cliff as talus.

Root wedging

The breaking up of rocks by growing tree roots.

Scarp

A rock or soil face left behind after a mass movement slides away.

Slide

A type of mass movement that has a relatively planar base as opposed to the curved base in a slump.

Slope

The angle of the land surface.

Slump

A type of mass movement that often has a curved base (as opposed to a planar base in a slide).

Soil

A mixture of weathered rock (sand, silt, clay) and organic debris.

Soil creep

A slow mass movement whereby soil flows slowly down a hillside over many years.

Soil horizon

A stratified layer in the soil.

Soilfall

When soil freefalls through the air (similar to a rockfall, except with soil).

Solifluction

A special type of soil creep and flow that occurs in areas with permafrost. In the summer, a thin upper layer of soil can thaw, but it continues to rest on frozen soil. If there is any slope, the thawed soil will creep.

Spheroidal weathering

A description of a weathering process whereby rocks erode into round or spherical shapes.

Talus

Loose material that accumulates at the base of a cliff, primarily due to rockfall.

Talus creep

A slow mass movement process whereby talus moves slowly towards the bottom of a slope.

Turbidity current

A rapid underwater flow of sand, silt, and clay that sweeps along the bottom of a water body. It does not carry as much material as a hyperconcentrated flow.

Unloading

When large amounts of rock or ice are removed from a surface.

Weathering

A mechanical or chemical process that breaks a larger rock down into smaller pieces or its chemical components.