Geology Exam 3 - Study Guide

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What is the connection between stress and brittle and ductile deformation?

Stress is the force applied to rock

brittle deformation occurs when rocks break (fracture) under stress, while ductile deformation occurs when rocks bend or flow without breaking.

Anticlines vs. Synclines—where are the oldest rocks? What is the form of the fold (like an A or a sink?)

Anticlines are arch-shaped (like an A) with the oldest rocks in the center; Synclines are trough-shaped (like a sink) with the youngest rocks in the center.

Brittle vs. Ductile deformational structures (strain).

Brittle strain produces faults and joints

Ductile strain produces folds.

Know all 5 of the different structures (Mnemonic: FFFFL).

Folds, Faults, Fractures (joints), Foliation, and Lineation.

Which two of these are only present in metamorphic rocks?

Foliation and lineation. (FFF - everything else FL - metamorphic)

Folds and oil: what is the connection?

Anticlines act as oil traps because the upward arching layers can catch and hold rising oil and gas.

Relationship between tectonic setting, stress type, and fault type (Table).

Divergent = Tensional Stress + Normal Fault

Convergent = Compressional Stress + reverse/thrust fault

Transform = Shear Stress + Strike-Slip fault

Tensional stress results in normal faults that usually happens at divergent boundaries.

At divergent boundaries, plates pull apart (tension), stretching the crust and causing blocks to slide down along normal faults.

Stress and strain.

Stress is the force per unit area acting on a rock.

strain is the change in shape or size resulting from that stress.

Upper crustal conditions vs. lower crustal conditions.

The upper crust is cool and brittle (favoring breaking); the lower crust is hot and under high pressure (favoring ductile flow).

Brittle vs. ductile deformation.

Brittle deformation occurs when rocks reach their elastic limit and fracture; Ductile deformation is a permanent change in shape without fracturing.

Different types of mass movements classified by movement speed, material type, and water.

Movements are classified as fast (rockfalls) or slow (creep), involving rock or soil/debris, and ranging from dry to water-saturated

Is an avalanche a landslide?

Yes, a debris avalanche is the most rapid and fluid type of mass movement.

List two types of fast landslides, list two types of slow landslides.

Fast: Rockfalls and Slumps

Slow: Creep and Solifluction.

List two human triggers, and two natural triggers.

Human: Oversteepening slopes and removing vegetation;

Natural: Heavy rainfall and earthquake

What is the difference between a rotational and translational landslide?

Rotational moves along a curved surface; T

Translational moves along a flat, planar surface

Angle of repose.

The steepest angle at which loose material remains stable (usually between 25° and 40°).

Talus.

Large piles of rock debris that accumulate at the base of steep cliff

What initiates landslides:

Excavation, or fill on hillside

Water leaks

Rainfall

Hot/cold temp variations (leads to expansion/contraction)

Fires followed by rain

Earthquakes

Erosion and Transport: bed load, suspended load, dissolved load.

Bed Load: large, along the bottom

Suspended load: small, in the water;

Dissolved load: Material in invisible solution.

Understand relationship between grain size and transport vs. deposition.

Fast water can carry big pieces.
When the water slows down, it drops them.

• Big grains (gravel) drop first

• Medium grains (sand) drop next

• Tiny grains (silt/clay) drop last

Valley: U vs. V shaped cross sections.

V-shaped valleys are carved by rivers;

U-shaped valleys are carved by glaciers.

What type of deformation are in the upper crust vs the lower crust?

The upper crust is cool and under low pressure, favoring brittle deformation. The lower crust is hot and under high pressure, favoring ductile deformation

How are different types of mass movements classified?

They are classified by the speed of movement (fast vs. slow), the type of material (rock, regolith, or mud), and the amount of water involved.

Is an avalanche a landslide?

Yes, an avalanche is a specific type of rapid mass movement involving snow, ice, or debris

What are the three types of sediment loads in a river?

Bed load (large particles rolling/sliding on the bottom),

Suspended load (fine particles floating in the water),

Dissolved load (ions in solution).

What are point bars and cut banks in a meandering channel?

Cut banks are on the outside of a meander loop where water flows fastest and erodes the bank.

Point bars are on the inside of the loop where water flows slowest and deposits sedime

Why are levees found on floodplains?

Natural levees form when a river overflows; the coarsest sediment is deposited immediately next to the channel. Humans build artificial levees to increase the channel's capacity and prevent flooding of the surrounding land.

How is river discharge determined?

discharge equation: Q= A x V, Q= discharge, A= cross-sectional area of channel, and V is the average velocity of water

Why do deltas form?

Deltas form when a river enters a standing body of water (like an ocean or lake). The velocity drops abruptly, causing the river to deposit its entire sediment load.

What is an ox-bow lake?

A U-shaped body of water that forms when a wide meander from the main river is cut off, creating a free-standing lake.

What are the reservoirs for water and the two biggest?

Reservoirs include oceans, ice, and groundwater.

The two biggest are saltwater = Oceans (~97%) and groundwater = Glaciers/Ice Caps (~2%).

What is the hydrologic cycle?

The movement of water through evaporation, transpiration, condensation, precipitation, runoff, and infiltration

What is a rain shadow and how does it form?

A dry area on the "back" side of a mountain; it forms when moist air rises, rains on the front (windward) side, and descends as dry air on the back (leeward) side.

What are the water resources in arid areas and Las Cruces?

Arid areas rely on groundwater and exotic streams. Las Cruces gets its water from the Mesilla and Jornada del Muerto aquifers and discharges it to the Rio Grande or for irrigation.

What rocks are more porous and permeable?

Sandstone and gravel are high in both; shale is porous but has very low permeability.

What parts of the crust have more water and what is the water table?

The upper crust has more water.

The water table is the top of the saturated zone; it rises in wet seasons and falls in dry ones.

What is the zone of aeration and a cone of depression?

The zone of aeration is the unsaturated area above the water table. A cone of depression is a dip in the water table caused by pumping a well faster than it recharges.

What is the problem with canals/reservoirs vs. groundwater storage?

Surface storage loses massive amounts of water to evaporation, whereas groundwater is protected from the sun.

How does groundwater get contaminated and why is the Rio Grande aquifer there?

Contamination comes from:

point sources (leaks) and non-point sources (farm runoff).

The aquifer exists because the Rio Grande Rift created a basin that filled with porous sediment.