Sedimentary Rocks, Processes, and Mass Wasting

Comprehensive vocabulary flashcards covering the formation of sedimentary rocks, clastic and chemical sediment types, lithification, and mass wasting triggers and engineering prevention methods.

Parent Rock

The preexisting source rock—which can be igneous, sedimentary, or metamorphic—prior to undergoing weathering and transformation into new rock.

Frost Wedging

A mechanical/physical weathering process where water seeps into rock cracks, freezes, expands, and exerts outward pressure to split the rock apart repeatedly (forming potholes).

Chemical Weathering

The decomposition of rock through chemical alteration and reactions, which is common in many environments (e.g., feldspar reacting with water and carbonic acid to yield kaolinite and dissolved ions).

Kaolinite

A soft, crumbly clay mineral formed when durable feldspar is chemically weathered by water and carbonic acid ($\text{H}_2\text{CO}_3$).

Saprolite Formation

A weathered rock profile applied to any rock that has undergone extensive chemical decomposition, literally meaning 'rotten rock.'

Erosion

The physical removal and transportation of sediment requiring energetic natural agents such as landslides, waterfalls, windstorms, and glaciers.

Basin

A natural low-lying depression or catchment area required for the accumulation and deposition of sediments.

Accommodation Space

The maximum volume or capacity of sediment that a depositional basin can physically hold before becoming full.

Subsidence

The gradual downward settling or sinking of the Earth's crust over time, which expands accommodation space and allows very thick sediment sequences to accumulate.

Strata (Beds)

Distinct, parallel horizontal layers of deposited sediment that stack and build upward over time.

Lithification

The complete geological transformation of unconsolidated sediment layers into coherent solid sedimentary rock via compaction and cementation.

Compaction

The stage of lithification in which accumulating overburden pressure compresses sediment grains together, reducing pore space and squeezing out pore fluids.

Cementation

The stage of lithification in which mineral-rich groundwater percolates through pore spaces, precipitating chemical coatings that bind loose sediment grains together into solid rock.

Detrital Sediment (Clastic Sediment)

Solid, loose mineral grains and rock fragments weathered from preexisting rock bodies and transported by wind, water, ice, or gravity.

Sorting

The degree of uniformity in particle size throughout a clastic sediment deposit, serving as an indicator of transport duration and erosional distance.

Rounding

The degree of edge smoothing and abrasion on individual sediment grains, reflecting sustained mechanical transport over time and distance.

Chemical Sediments

Sedimentary materials formed from chemical precipitation, dissolution, or saltwater evaporation (e.g., salt flats in Utah), typically composed of a single dominant mineral type.

Biogenic Sediments (Bioclastic Sediments)

Sediments derived from the accumulated organic remains or hard mineral skeletons of once-living organisms, such as carbonate shells and vegetative debris.

Coal

A biogenic, carbon-rich sedimentary rock formed from ancient compressed plant remains that does not fizz or react with acid.

Angle of Repose

The steepest angle relative to the horizontal plane at which a loose, granular material remains stable without slumping or sliding downhill (typically around $35^\circ$).

Mass Wasting

The downslope movement of rock, regolith, and soil under the direct pull of gravity, classified primarily by the material involved, movement mechanism, and velocity.

Rockslide

A rapid mass wasting event where a coherent, intact block of solid rock detaches and slides along an inclined slope surface.

Rockfall

A mass wasting process where dislodged bedrock fragments plummet in freefall down a vertical or near-vertical cliff face.

Creep

The slow, continuous downhill migration of soil and regolith over time, typically evidenced on the surface by leaning fence posts, tilted poles, or bowed trees.

Mud Flow

A rapid downhill flow consisting of water saturated with at least $60\%$ fine-grained material, such as mud and clays.

Debris Flow

A moving mass of saturated sediment containing a high concentration of coarse, large particles, such as boulders and uprooted tree trunks.

Drainage Control

An engineered slope stabilization method using horizontal drains (hydraugers) and vertical pumped drains to remove excess groundwater and reduce destabilizing pore pressure.

Retaining Wall

A rigid structural barrier constructed at the base of slopes and roadcuts to physically support and resist the lateral pressure of destabilized soil and rock.

Rock Bolts

Long steel fastening rods anchored deep into stable bedrock to pin loose, fractured surface slabs directly to the interior cliff face.

Thistle, Utah Landslide (1983)

A historic mass wasting failure in a known unstable area causing $\$200\text{ million}$ in damage, which had been deemed preventable with $\$0.5\text{ million}$ of proper drainage systems.