Environmental Geology Exam 3 Flashcards

Flow eruptions

Coherent lava that is nonexplosive, branching lobe, and sheet-like

Domes eruptions

Circular mound-shaped coherent lava, more viscous (and dome collapse can trigger pyroclastic flows)

Pyroclastic

Fragments of igneous rocks are ejected from explosive volcano

Importance of volcanic gases

• Hazardous since they are denser than atmospheric gasses and collect in depressions, hugging the ground, and suffocating organisms

• Change in character can sere as eruptions precursor

• Larger eruptions influence weather locally & globally

• Long term primary source for atmosphere and hydrosphere

Types of Volcanos

Shield Volcanos:

• Low angle slopes

• Dominated by flows

• smaller cinder cones common associate

• Made up of basalts

Stratovolcanos:

• Higher angle slopes

• Dominated by pyroclastic rocks

• Explosive eruptions

• Larger calderas

• Made up of andersite & rhyolite

Basalts

• Low viscosity

• High extrusion temp

• Primarily flow

• Denser

• 48-52% SiO2 content

• Dark blackish color

Andersite & Dacite

• Medium viscosity

• Medium extrusion temp

• Primarily as domes & pyroclastics

• Less dense

• 52-68% SiO2 content

• Grey in color

Rhyolite

• High viscosity

• Low extrusion temp

• Primarily as domes & pyroclastic

• Lower density

• Light grey/reddish colored

Super volcanos

Eruptions of magnitude 8 on volcano explosively meaning <1000 km2 of magma are erupted

Hydrothermal Circulation associated w/ volcanoism

• magma chamber @ depth provides source of eruption material

• Hydrothermal circulation cell: magma chamber heats surrounding groundwater as hot air rises, setting a circulation of water through fractures and cavities of rock

Volcanic geohazards

Lava flows: slow moving ,can block roads, burn crops & homes

Volcanic gases: dense & collect “death” gullies released from caldera lakes

Lahars: intermediate speeds, long runouts, and follow drainage can destroy structures along rivers and contribute to dam failure

Ash: Travels far, can load on structures and collapse, health consequences and damage machinery, siltation changes river behaviors and habitat, and fertilizes plankton growth

Mitigation of volcanic geohazards

• Monitoring & warning systems (responsibility of USGS in US)

• Evacuation plans/facilities (produce hazard maps/models)

• Public edu. abt possibility and how best to respond

• Zoning (restriction of placement of critical facilities in certain areas)

Global climate & massive eruptions

Areas unaffected w/ volcanism can still be affected by catastrophic large eruptions bc eruptions send gas & ash into stratosphere that reflects sunlight causing global cooling of several C temp

Source rock

Organics need to be preserved in the rocks that happens in euxinic (O-poor) environments w/ slower anaerobic decay that factors preservation found in restricted marine bodies or lakes

• Sulfur compounds are common in euxinic environments

• Need a subsiding depression to bury and preserve the sed. & fossil organics

• Black shales/limestone are common source rocks—often stinky when breaks fresh face open

• Some 50% of source rocks formed in Cretaceous period

Thermal window history

Kerogen: Waxy and complex organics in source rock (immobile)

• Kerogen need to be cooked into oil (low simmer) or gas (hotter)

• Cooking increases mobility of organics, but temps too high can change organics into less useful forms

Reservoir/ Trap

Need reservoir rock and seal that the mobilized oil &/ gas collect in

• Stratigraphic traps (e.g. reefs, channels, or offshore sand bodies) that have porosity

• Structural traps: the classic anticline

Fracking technologies

1. Directional drilling- drills stem can be bent so it’ll drill along a oil rick layer for substantial lengths

2. Fracking by pumping water under high pressures that it intensely fractures the surrounding layers, creating a fracture porosity and permeability

3. Propants- Sand or other grains are included in water and left behind in the cracks to prop them open as pressure in reduced by pumping

4. Chemical additives- decrease the viscosity of oil making it easier to flow and pump, and biocides (active substances, including microorganisms that eliminate harmful organisms) so that microbial sludge won’t grow and plug up the works

Coal formation

Coal forms from peat, which forms in swamps, fens, and other types of wetlands

• Euxinic waters (no O2, slow anaerobic decay generates CH4, partial organics accumulation to form peat

Peat→ lignite (soft brown coal)→ bituminous coal (black, harder)→ anthracite (black shiny)

—————————— (Compacting & heating w/ geological burial)——— ———→

Coal quality

Energy content: measured as btu (British thermal unit)/ pound, higher energy=better function of coal

Mineral content: flood in swamp can intro. mud w/ minter matter dispersing in coal, burnt forms fly ash that must be dealt

Sulfur content: Due to mineral pyrite that forms in euxinic enviro. contributes to acid mine runoff & rain. Coal from coastal swamps have more sulfur

coal exploration

• surface geological mapping

• drilling

• have 100s of yrs of reserves (known as deposits in the ground) @ present U.S. rich in coal

• Look for old deltas w/ unifromitanism

coal extraction

1. Underground: Typically $$$, but necessary if coal is @ depth. Enviro. Cost: Coal mine fires & explosions, black lung disease, coal mine collapse & surface subsidence

2. Surface/ Strip mining: $, safter for miners, works in shallow coal. Enviro. Cost: Destruction of surface soil & biota, acid mine tailing (waste rock from mine) drainages, and groundwater changes

Acid mine runoff

Mine runoff pH is typically 5, 3, and 2 (acidic)

• Occurs not only w/ coal mines, but also common w. other mines

• pyrite and other sulfide mineral entailing are culprits as they weather easily, oxidizing, and producing acidic water

• Only extremophile microbial life can live in very acidic water, leach, and mobilize heavy metal

Acid mine runoff mitigation

limestone helps neutralize (geologic anti-acid)

Reclamation- returning of the mine land to some useable & desired form

• Reshaping the landscape to desire from

• Replacing topsoil (saved)

• Seeding and/planting

• Water to est. veg

• monitoring

coal processing

Includes crushing, screening, and washing. Separation of lighter coal from heavier mineral

• Sometimes use chem for frothing & flocculation, which aids separation (e.g MCHM is a coal cleaning chem)

Coal use

Particulate air pollution:

• sig. health consequences

• scrubbers (filters) clean power plant emission

• High smoke stacks emit at high altitudes

Acid rain (Sulfuric acid):

• Due to sulfur content of coal

• widespread footprint

• acidifies lakes & inf. tree health

• mobilizes toxic forms of (Al)

Mercury Contamination:

• @ low lvls in coal, but higher in backgrown

• increasing lvls seen in lake sed. & biota

• Hg bioaccumulates

disposal of coal waste

Coal ash either repurposed for most beneficial use (e.g cement) or storage in landfills

Nuclear proliferation

Plutonium- (can be) byproduct of nuclear operation that is very toxic & radioactive isotope

• used as fuel for breeder reactor tech

• Easily use to make nuclear bomb (must keep hidden)

Basic of radioactivity

Isotope- dif. Version of an element that has dif # of neutron and can be stable/unstable

• Unstable isotopes “decay”- releases radiation and heat @ exponential decay rate (half life)

• parent isotopes decays to daughter isotopes that is either radioactive/not (e.g uranium decays → stable lead isotope)

Forces vs. spontaneous decay & nuclear power

• Atom bombs are critical masses, w/ exponential release of energy

• Atomic power plants are sub-critical masses w/ constant and controllable energy release

• Fuel & control rods in reactors absorb some radiation

• Nuclear power plants are steam generators w/ H2O heated by reactors, where subcritical masses accelerate decay producing heat in controlled fashion

Radon

Naturally occurring radioactive gas

• forms from U-238 decay

• Lung cancer is correlated w/ prolong radon exposure

Mining fuel for nuclear power

• Carnotite is common ore w/ various U oxide minerals

• Crow Butte deposit is major U producers: euxinic causes U oxides to from while O rich waters dissolve and mobilizes U

Environmental concerns:

• Waste rock can be enriched in U & other radioactive minerals

• Oxidation mobilizes U → mining & exposure of rocks w/ increased surface area may cause increased U to move into groundwater

• Radon exposure of miners

Designing high lvl waste site

(e.g. Yucca Mount) includes: No seepage of H2O through site (low permeability), position & stability of groundwater table, possibilities of volcanic & seismic activity, and low pop density

Low lvl radioactive waste

Material containing small concentration of radioactive substances, typically not requiring safety matures

Low lvl radioactive waste policy act of 1980: federal legislation est 5 states compact. By 1996 and non-member states chosen and dev disposal facility site that assumes title to a liability for all low lvl waste generated within boarders

Boyd county (NE’s compact site)

• selected by consulting firm Bechtel Inc.

• Pierre shale bedrock in Boyd county was host rock

• Design focus on enhanced above grade vaults

• Shallow perched aquifers, wetlands exist in area

• NE denied permission for facility to be built, was sued by compact and had to pay $151 M & litigation cost of $25 M