Geology: Mass Movement, Coastal Defense, and Glaciers

Vocabulary flashcards covering mass movements, slope mechanics, coastal hazard mitigation, and glacial dynamics and features.

Mass Movement (Mass Wasting)

The movement of geologic material downslope under the direct influence of gravity, which can range from slow and cumulative processes like soil creep to swift events like rockfalls and avalanches.

Landslide

A general term used to describe the results of rapid mass movements of rock and soil downhill.

Shearing Stress

The downslope pulling force exerted on slope materials by gravity, governed by the mass of the material and the steepness of the slope angle.

Shear Strength

The internal frictional resistance within a slope material that counteracts shearing stress and prevents sliding.

Angle of Repose

The maximum slope angle at which an unconsolidated material remains stable without sliding downhill.

Quick Clay

A fine-grained sediment formed from glacial rock flour deposited in marine environments and bound by sea salt; once uplifted and leached by fresh water, it becomes structurally unstable and prone to sudden liquefaction.

Rockfall

A rapid mass wasting process where rocky material detaches from a cliff or steep slope and undergoes free-falling motion without remaining in contact with the ground surface below.

Talus

A pile or apron of coarse, angular rock debris that accumulates at the base of a cliff or steep slope due to recurrent rockfalls.

Slide

A mass movement characterized by the translational downward movement of a cohesive block of rock or soil along a discrete, planar surface such as a bedding plane.

Slump

A mass movement, typically occurring in soil, characterized by rotational motion along a curved failure surface, leaving an exposed scarp at the top and an earthflow at the toe.

Creep

Extremely slow downslope displacement of soil or rock (typically less than $1\,\text{cm/yr}$), often driven by repeated cycles of freezing and thawing (frost heave) or prolonged gravity-induced stress.

Flow

A type of mass movement where unconsolidated material travels in a chaotic, incoherent manner with fluid-like mixing of particles, including mudflows, debris flows, and avalanches.

Nature-Based Coastal Defense

The use of natural coastal habitats to buffer waves: coral reefs reduce wave energy by up to $97\%$, mangroves reduce wave height by up to $66\%$, and coastal marshes attenuate up to $50\%$ of smaller wave energy.

Glacier

A large, persistent mass of ice that forms on land through the compaction of snow and moves downhill or outward under its own weight in response to gravity.

Alpine Glacier

A relatively small mountain or valley glacier that occupies steep alpine topography and flows confined between mountain walls.

Continental Glacier

A massive ice sheet or ice cap exceeding $1\,\text{km}$ in thickness that spans regional or continental scales, currently found only on Greenland and Antarctica.

Equilibrium Line

The dividing boundary on a glacier that separates the upper zone of accumulation (net mass gain) from the lower zone of ablation (net mass loss).

Meters Water Equivalent ($\text{m w.e.}$)

A metric used in glacier mass balance calculations reflecting the average surface-wide change in ice thickness converted into the equivalent thickness of liquid water.

Till

Unsorted and unstratified sediment deposited directly by melting glacial ice, consisting of a heterogeneous mixture of particle sizes ranging from fine clay to large boulders.

Outwash

Glacial sediment that is washed out, sorted, and redeposited by meltwater streams emerging from the glacial margin, commonly forming a braided plain.

Moraine

A ridge or landform constructed of unsorted glacial till deposited at the margin or along the margins of an active or retreating glacier.

Terminal Moraine

An end moraine ridge marking the outermost edge and maximum advance distance reached by a glacier.

Recessional Moraine

An end moraine ridge deposited during a temporary standstill or readvance period that occurs during the overall retreat of a glacier.

Glacial Abrasion

Erosion that takes place when rock particles held in the base of moving glacial ice drag against and grind the underlying bedrock surface.

Glacial Plucking

The erosional process whereby pressurized meltwater penetrates rock joints beneath an advancing glacier, freezes, and tears loosened rock blocks directly into the ice flow.

Glacial Striations

Parallel linear grooves or scratches gouged into bedrock surfaces by rock debris trapped at the base of flowing ice, demonstrating past ice movement direction.

Calving

The mechanical detachment of ice blocks from the terminus of a glacier or ice shelf when it flows into a body of water, creating floating icebergs.

Dropstone

An anomalous pebble, cobble, or boulder that drops from melting floating icebergs into otherwise fine-grained, horizontally bedded lake or marine sediments.