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Geol quiz 4
words about water
| Question | Answer |
|---|---|
| Lag time | time it takes for rain to be absorbed into ground |
| Lag time for flooding | lag time decreases and discharge increases |
| Groundwater | water beneath the water table, top of saturated zone |
| What allows ground water to flow? | porosity and permeability, both must be high |
| Porosity | percent of void space in rock or sediment, what isn’t solid, ex. Sandstones and limestones, but most igneous and sedimentary rocks are low |
| Permeability | the interconnectedness of the void spaces |
| Aquifer | water-rich rock layer |
| Aquitard | water-poor rock layer |
| Unconfined aquifer | has no confining layer on top |
| Confined aquifer | sandwiched by confining layers |
| High-plains aquifer | (Ogallala) used for irrigation in NE, KS, OK, & TX |
| Water table | top surface of the saturated zone |
| How WT related to surface topography? | WT mimics surface topo. in humid regions, total elevation difference is not as extreme in WT vs topo., WT topo is maintained bc GW flow is slope and can’t return to flat |
| Why does GW flow in unsaturated zone? | gravity pulls moisture downward |
| Why does GW flow in saturated zone? | gravity and water pressure from weight of water |
| If WT is flat | no flow of GW |
| Hydraulic head | total energy available to drive GW flow (in saturated zone), combo of elevation head and pressure head |
| Ground water flow | usually from a high WT elevation to a low WT elevation along, curved, concave up pathways |
| Recharge areas | high elevation areas |
| Discharge areas | low elevation areas |
| How fast does GW flow? | rule of thumb- 1 inch-1foot per day |
| GW flow rate depends on | hydraulic gradient= difference in total head between 2 pts/distance between 2 pts |
| Henry P.G. Darcy | 1850s French Engineer (1803-1858), Field studies near Dijon, conducted lab experiments on rate of WT thru sediments, developed basic equation for rate of GW flow |
| Darcy’s law | Discharge=hydraulic gradient*hydraulic conductivity*area across which water flows |
| Hydraulic conductivity | ability of sediment to transport water, depends on properties of water and solid aquifer |
| How to retrieve GW | wells, cased with plastic, and sand screen at the bottom |
| Cones of depression | how the water table shapes around a well |
| Drawdown | the elevation of the water table lowering |
| Artesian well | (municipal well) drilled into a confined aquifer, with water tank and water main |
| Potentiometric surface | like a water table in a well of water tank, falls off the further away you are, in a confined situation |
| Standpipe | gauges how high the water level is in municipal well |
| Natural artesian well | recharged from rain water, with non-flowing and flowing |
| Problems associated with GW supply and usage | lowering of WT, habitat destruction, saltwater intrusion, reversal of flow direction, aquifer collapse, poor GW quality |
| Lowering of WT | overusage, creates cones of depression |
| Habitat destruction example | Florida everglades |
| Saltwater intrusion example | Biscayne Aquifer in Florida and also bad in Los Angeles |
| Virginia’s impact structure | partly controls intrusion |
| Aquifer collapse | land subsidence, happens when too much water is pumped out, ex. Leaning tower of Pisa, Venice, subsidence in San Joaquin, CA |
| Mass wasting | gravity driven transport of debris |
| How to distinguish difference in mass movement | velocity, location, behavior of debris, debris type |
| Sub-aerial | on land |
| Debris types | rock, snow, soil |
| Behaviors | solid, slurry, or cloud |
| Creep | freeze thaw cycles in temperate regions, debris moves outward as ice expands (soil moisture), slow, solid, soil and sediment |
| Examples of creep | curving tree trunks, tilted power lines, cracked foundations, tilted walls, tilted gravestones |
| Slumps | results from a mass of soil/seds that slide up on a curved detachment surface (concave up), slow, solid, soil and sediment |
| Examples of slumps | headscarp-kind of like a mini cliff |
| Mudflows and debris flows | soil/seds with larger clasts that flow, flows follow topography and are fan shaped, fast, wet slurry, any debris, a lot in CA |
| Landslides | rock/soil that rides on an air cushion, very fast, solid, anything solid (rock, soil) |
| Landslide examples | more in Appalachians and on west coast, Thistle, UT in 1983, Madison County, VA |
| Avalanches | debris (suspended in air) moves quickly as a cloud, very fast, cloud, anything (snow, ice, rock) |
| Rock falls | free falling rock, cliffs, very fast, solid, rocks |
| Can they appear in submarine locations? | Yes all, cause Tsunami hazards |
| Case study Hawaii | submarine slumps and debris avalanches, last major one 105,000 yrs ago, evidence in New South Wales, Australia, possible 100,000 yr recurrence interval, Hilina Slump |
| Tsunami | rapidly rising wall of water, debris filled usually, doesn’t curl, can’t be surfed |
| Causes of tsunamis | Earthquakes, volcanos, meteorites, slides |
| Storegga slide | occurred in the North sea |
| Case study Canary Islands | La Palma Island is possibly biggest threat to the Atlantic, 10 major slides in last 1 mill. Yrs |
| LiTuya Bay, Alaska 1958 | earth quake related landslide into Bay, bay is 7 mi long and 2 mi wide, large tsunami |
| Causes of mass wasting | weathering, shrink-swell clays (expand/contract), groundwater/saturated soil/rock, vibration, steep weak surfaces |
| Weathering | weakens bond in mineral rocks |
| Vibration | “quick clay” or “liquefaction” of sediments |
| Steep weak surfaces | metamorphic foliation, sedimentary layers, joints (fractures) |
Created by:
lfalkens
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