Geology Summative Assessment 4

Resources

things necessary or important to life and civilization

Reserves

the quantity of geologic material that has been found and can be recovered economically

Subeconomic resources

geologic materials that have been found, but cannot be reasonably obtained and/or sold

Ore

a valuable/useful metal occurring at a high enough concentration that it’s worth mining

Pegmatite

an intrusive, igneous rock with very large crystals

What can the uncommon ores often found in pegmatite be used for?

radios, toilets, technology, etc.

Conflict minerals

Sales of mineral resources that sometimes support violence or unethical practices

Examples of conflict minerals

Mica, cobalt, ‘blood’ diamonds, oil

Underground mines

• Mostly entrance and waste rock piled up

• Shafts can be sealed and returned to pre-mine conditions

• Sometimes collapse (structural integrity or groundwater)

• Can contaminate groundwater

• Make less apparent changes to environment

Surface mines

• Practical when materials are near the surface

• Permanently changes topography

• Potentially release toxins and pollutants into surface run off

• Typically quarries or strip mines

Tailings

• Piles of unwanted materials

• Can lead to acid drainage

• Can expose water to mercury, arsenic, cadmium, and uranium

What element used to be used to extract gold and what element is used now instead?

Mercury, cyanide

Hydrosphere

• All the water at and near the Earth’s surface

• Quantity stays essentially constant

Hydrologic cycle

• The cycle which water in the hydrosphere moves

• Includes evaporation, precipitation, and surface groundwater runoff

• Oceans: 97% of all water

• Lakes and streams: 0.016%

Stream

a generic name for flowing water in a channel

Drainage basin

• The source of a stream’s water

• Tells you where it’s headed after the fact

Divide

where two drainage basins meet, determining where water will go

Stream size is dependent on:

• Size of drainage basin

• Climate (precipitation vs. evaporation)

• Vegetation

• Local geology (type of rock)

Streams carve a…

channel

Discharge

volume of water flowing through a stream over a period of time

Capacity

total amount of material (not water) a stream can move

Load

amount of material that a stream is actively carrying

Gradient

• Steepness of the stream channel

• Rise over run

• When all else is equal, the higher the gradient, the faster the stream goes

Water doesn’t ever go perfectly straight, it forms

meanders

Water is faster at ____, slower at ____

cut banks, point bars

Floodplain

a flat region or valley floor surrounding a stream channel into which streams overflow during flooding

Flooding

when a stream overflows its banks

Surface runoff is affected by…

porosity, permeability, vegetation, topography, and weather

Porosity

percentage of empty space in rock, sediment, or soil

Permeability

• How easily fluids can travel through rock, sediment, or soil

• A path that water can travel along

How does vegetation affect flooding?

Plants provide a physical barrier and increase permeability

How does topography affect flooding?

Steep topography leads to more surface runoff

Stage

the elevation of the surface of the water

Upstream Floods

• Typically small, localized flooding

• Typically form from sudden intense storms or dam failures

Downstream Floods

• Typically large stream systems or drainage basins affected by flooding

• Usually last longer than upstream floods

Flash Floods

• Type of upstream flood

• Rapid rise in stream stage

• Typically close to a weather event or massive water input (dam failure)

• Occur anywhere that surface runoff is rapid, large volume, and confined

Why do flash floods happen in urban areas?

Lots of concrete, asphalt, and other typically impermeable surfaces

How can the water table vary?

It can rise and fall based on rainfall, drought, pumping, and seasonal changes

How are confined aquifers recharged?

Through areas where the aquifer's impermeable layer is exposed or cracked

What problems are associated with karst aquifers?

They are prone to contamination and sinkholes due to their porous limestone structure

What is groundwater flow?

Movement of water through the soil and rocks beneath the Earth's surface

What is subsidence caused by groundwater withdrawal?

The ground sinks when too much groundwater is pumped out

How is Earth’s water distributed?

97% saltwater in oceans, 3% freshwater (mostly ice and groundwater)

How does a sinkhole form?

• Dissolution: Water dissolves soluble rock (like limestone) underground, creating cavities.

• Cavity Enlargement: The cavities grow as more rock dissolves, forming an underground void.

• Surface Weakening: The ground above the cavity becomes unstable as support is lost.

• Collapse: The surface suddenly sinks or collapses into the cavity, forming a sinkhole.

What determines water quality?

The amount and type of impurities in the water

Why might groundwater be preferred over surface water?

It's naturally filtered, more protected from pollution, and available year-round

Karst terrain

A landscape formed primarily from the dissolution of soluble rocks, like limestone or gypsum

Karst terrain geological features

Sinkholes, caves and caverns, disappearing streams, spring systems, and limestone pavements

Unconfined aquifer

An aquifer that has no impermeable layer above it, allowing water to flow in easily

What happens when impermeable cover is over an aquifer recharge area?

It prevents rainwater from soaking in, reducing groundwater recharge

What are average annual precipitation trends in the U.S.?

More in the East and less in the West

Artesian system

A confined aquifer where water rises under pressure without pumping.

What geologic properties affect porosity and permeability?

Grain size, shape, and how tightly packed the material is

Groundwater contour map

A map showing water table elevation to understand groundwater flow

Confined Aquifer

An aquifer trapped between two impermeable layers, under pressure

Why is subsidence often irreversible?

Once the ground compacts, it can’t return to its original height

Link between wetlands and aquifers

Wetlands can recharge aquifers and store excess groundwater

How does a cone of depression form?

When water is pumped from a well faster than it can recharge

Potentiometric surface

The level water will rise to in a well from a confined aquifer

Describe clay’s porosity and permeability

Clay is porous but has low permeability, meaning water moves through it slowly

How does groundwater elevation drop relate to irrigation?

Heavy irrigation can lower the groundwater level, causing drops

ppb and ppm

Parts per billion and parts per million, units for measuring water contaminants

Is bottled water safer than tap water in the US?

No, they are regulated similarly and can be of equal quality

Saltwater intrusion

When saltwater enters freshwater aquifers, often due to overpumping near coasts

What sector uses the most groundwater?

Agriculture, especially for irrigation

Water use vs. water consumption

Use includes all water taken from sources; consumption is water that doesn’t return to the source

Aquifer

An underground layer that stores and transmits groundwater

Can natural sources cause water contamination?

Yes, such as radioactive minerals from rocks

Groundwater recharge vs. discharge

Recharge is water entering an aquifer; discharge is water leaving it

Hard water

Water with high levels of calcium and magnesium