Geology 1405: Subsidence and Groundwater

This set of vocabulary flashcards covers key concepts of land subsidence, soil profiles, karst topography, and environmental hazards as detailed in Geologic & Environmental Hazards Lesson 8.

Subsidence

Ground failure characterized by nearly vertical deformation or the downward sinking of earth materials.

Soil (Geologist Definition)

Rocky earth material that has been altered by weathering and serves as a medium for water transport and storage.

Soil (Engineer Definition)

Any solid earth material that can be manipulated or removed without blasting.

O Horizon

The organic layer of a soil profile consisting entirely of plant litter and other organic material.

A Horizon

Also known as topsoil, this layer contains both organic and mineral material.

E Horizon

The eluviated horizon or zone of leaching, characterized as a light-colored layer of leached inorganic components.

B Horizon

The subsoil or zone of accumulation, often enriched in clay minerals and calcium carbonate moved downward from top layers.

C Horizon

The layer consisting of parent material that is partially altered by weathering processes.

R Horizon

The layer of unaltered parent material or consolidated bedrock that is impermeable and composed of compacted or cemented material.

Soil Texture

The fineness or coarseness of soils determined by the relative proportions of sand-, silt-, and clay-sized particles.

Clay

Soil particles with a diameter less than $0.004\,\text{mm}$, visible only under a microscope.

Silt

Soil particles with a diameter between $0.004\,\text{mm}$ and $0.074\,\text{mm}$, visible with a $10\times$ hand lens.

Sand

Soil particles with a diameter between $0.074\,\text{mm}$ and $2.0\,\text{mm}$, visible to the naked eye.

Moisture Content

The amount of water in a soil, which is critical to its strength and potential to shrink or swell.

Soil Erosion

The removal of mineral, organic, and soil material at a rate faster than it is being produced.

Karst

A landscape characterized by the dissolution of soluble bedrock, such as limestone, dolostone, marble, gypsum, and halite, by groundwater.

Solutional Sinkholes

Depressions formed when acidic groundwater becomes concentrated in holes in joints and fractures in rock.

Collapse Sinkholes

Depressions that develop by the collapse of surface material into an existing underground cave.

Frost Heaving

The upward movement of soil particles and land surface caused by a volume increase of approximately $9\%$ when water freezes.

Permafrost

Sediment or soil cemented with ice that remains frozen for at least $2$ years.

Thermokarst

Uneven soil and terrain created by the extensive melting of permafrost.

Expansive Soils

Soils, often containing smectite group clays, that expand during wet periods and shrink during dry periods.

Groundwater Mining

The excessive extraction of groundwater leading to the compaction of rocks and land subsidence.

Moses Project

An expensive $\$7\,\text{billion}$ floodgate project designed to combat flooding in Venice.