Geology3

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metamorphism

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The transition of one rock into another by temperatures and/or pressures unlike those in which it formed

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hydrothermal metamorphism

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– chemical alterations from hot, ion-rich water

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regional metamorphism

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Occurs during mountain building
Produces the greatest volume of metamorphic rock
Rocks usually display zones of contact and/or hydrothermal metamorphism

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heat

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Most important agent
Recrystallization results in new, stable minerals

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chemically active fluid

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Mainly water with other volatile components
Enhances migration of ions
Aids in recrystallization of existing minerals

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sources of fluids

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Pore spaces of sedimentary rocks
Fractures in igneous rocks
Hydrated minerals such as clays and micas

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foliation

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any planar arrangement of mineral grains or structural features within a rock

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porphyrytic texture

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Large grains, called porphyroblasts, surrounded by a fine-grained matrix of other minerals

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phyllite

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Gradation in the degree of metamorphism between slate and schist
Platy minerals not large enough to be identified with the unaided eye
Glossy sheen and wavy surfaces
Exhibits rock cleavage
Composed mainly of fine crystals of muscovite and/or chlorite

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schist

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Medium- to coarse-grained
Platy minerals (mainly micas) predominate
The term schist describes the texture
To indicate composition, mineral names are used (such as mica schist)

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gneiss

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Medium- to coarse-grained
Banded appearance
High-grade metamorphism
Often composed of white or light-colored feldspar-rich layers with bands of dark ferromagnesian minerals

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marble

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Coarse, crystalline
Parent rock was limestone or dolostone
Composed essentially of calcite or dolomite crystals
Used as a decorative and monument stone
Exhibits a variety of colors

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quartzite

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Formed from a parent rock of quartz-rich sandstone
Quartz grains are fused together

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migmatites

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Highest grades of metamorphism that is transitional to igneous rocks
Contain light bands of igneous components along with areas of unmelted metamorphic rock

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the role of water

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Diminishes particle cohesion (friction)
Water adds weight

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slump

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Movement of a mass of rock or unconsolidated material as a unit along a curved surface
Occurs along oversteepened slopes

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rockslide

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Blocks of bedrock slide down a slope
Generally very fast and destructive

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debris flow

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Consists of soil and regolith with a large amount of water
Often confined to channels

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earthflow

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Form on hillsides in humid regions
Water saturates the soil
Commonly involve materials rich in clay and silt

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creep

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Gradual movement of soil and regolith downhill
Aided by the alternate expansion and contraction of the surface material

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soliflucation

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Promoted by a dense clay hardpan or impermeable bedrock layer
Common in regions underlain by permafrost
Can occur on gentle slopes

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ground water

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found in the pores of soil and sediment, plus narrow fractures in bedrock
- largest reservoir of fresh water that is readily available to humans

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belt of soil moisture

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water held by molecular attraction on soil particles in the near-surface zone

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zones of saturation

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form when water reaches a zone where all of the open spaces in sediment and rock are completely filled with water

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water table

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the upper limit of the zone of saturation

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capillary fringe

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-Extends upward from the water table
-Groundwater is held by surface tension in tiny passages between grains of soil or sediment

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zones of aeration

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-Area above the water table
-Includes the capillary fringe and the belt of soil moisture
-Water cannot be pumped by wells

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gaining streams

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gain water from the inflow of groundwater through the streambed

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losing streams

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gain water from the inflow of groundwater through the streambed

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porosity

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percentage of total volume of rock or sediment that consists of pore spaces
-Determines how much groundwater can be stored
-Variations can be considerable over short distances

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permeability

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the ability of a material to transmit a fluid

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aquatard

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an impermeable layer that hinders or prevents water movement (such as clay)

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aquafir

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permeable rock strata or sediment that transmits groundwater freely (such as sands and gravels)

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Darcy's Law

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If permeability remains uniform, the velocity of groundwater will increase as the slope of the water table increases

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hydraulic head

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the vertical difference between the recharge and discharge points

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hydraulic gradiant

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the water table slope, determined by dividing the vertical difference between the recharge and discharge points by the length of flow between these points

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springs

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Occur where the water table intersects Earth’s surface
Natural outflow of groundwater
Can be caused by an aquitard creating a localized zone of saturation which is called a perched water table

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hot springs

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Water is 6-9oC warmer than the mean annual air temperature of the locality
The water for most hot springs is heated by cooling of igneous rock

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geysers

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Intermittent hot springs
Water erupts with great force
Occur where extensive underground chambers exist within hot igneous rock
Groundwater heats, expands, changes to steam, and erupts

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Artestian Well

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a situation in which groundwater under pressure rises above the level of the aquifer

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types of Artesian Well

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Nonflowing – pressure surface is below ground level
Flowing – pressure surface is above the ground

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Subsidence

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Ground sinks when water is pumped from wells faster than natural recharge processes can replace it (San Joaquin Valley of California)

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saltwater contamination

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Excessive groundwater withdrawal causes saltwater to be drawn into wells, thus contaminating the freshwater supply
Primarily a problem in coastal areas

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caverns

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Most caverns are created by acidic groundwater dissolving soluble rock at or just below the surface in the zone of saturation

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Karst topography

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Landscapes that have been shaped mainly by the dissolving power of groundwater

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glacier

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a thick mass of ice that originates on land from the accumulation, compaction, and recrystallization of snow

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Valley (alpine) glaciers

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Exist in mountainous areas
Flow down a valley from an accumulation center at its head

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ice sheets

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Exist on a larger scale than valley glaciers
Two major ice sheets on Earth are over Greenland and Antarctica

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steps in glacial ice formation

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-Air infiltrates snow
-Snowflakes become smaller, thicker, and more spherical
-Air is forced out
-Snow is recrystallized into a much denser mass of small grains called firn
-Once the thickness of the ice and snow exceeds 50 meters, firn fuses into a solid mass of interlocking ice crystals

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plastic slip

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Occurs within the ice
Under pressure, ice behaves as a plastic material

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basal slip

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Entire ice mass slipping along the ground
Most glaciers are thought to move this way by this process

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zone of accumulation

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-The area where a glacier forms
-Elevation of the snowline varies greatly

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zones of wastage

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the area where there is a net loss to the glacier due to Melting, calving

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calving

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– the breaking off of large pieces of ice (icebergs where the glacier has reached the sea)

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glacial budget

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Balance, or lack of balance, between accumulation at the upper end of the glacier, and loss at the lower end is referred to as the

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plucking

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lifting of rocks

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abrasion

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Rocks within the ice acting like sandpaper to smooth and polish the surface below

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glacial drift

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refers to all sediments of glacial origin
-stratified
-till

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stratified drift

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sediments laid down by glacial meltwater

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till

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material that is deposited directly by the ice

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drumlins

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Smooth, elongated, parallel hills
Steep side faces the direction from which the ice advanced
Occur in clusters called drumlin fields
Formation not fully understood

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4 main stages of ice age in america

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Nebraskan
Kansan
Illinoian
Wisconsinan

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indirect effects of ice age glaciers

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-Forces migration of animals and plants
-Changes in stream courses
-Rebounding upward of the crust in former centers of ice accumulation
-Worldwide change in sea level
-Climatic changes

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Milankovitch hypothesis

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-Shape (eccentricity) of Earth’s orbit varies
-Angle of Earth’s axis (obliquity) changes
-Earth’s axis wobbles (precession)
-Changes in climate over the past several hundred thousand years are closely associated with variations in the geometry of Earth’s orbit

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processes involved in hydrologic cycle

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-precipitation
-evaporation
-infiltration
-runoff
-transpiration

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fractionation

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physical and chemical processes that result in a redistribution of the stable isotopes of an element in a compound.

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infiltration capacity is controlled by...

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-intensity and duration of rainfall
-prior wetted condition of the soil
-soil texture
-nature of the vegetative cover

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stream discharge

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Width x Depth x Velocity

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stream erosion

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lifting loosely consolidated particles by abrasion and dissolution

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competence

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indicates the maximum particle size a stream can transport
-determined by streams velocity

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alluvian fans

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develop where a high-gradient stream leaves a narrow valley
-sopes outward in a broad arc

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deltas

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forms when a stream enters an ocean or lake
-forest beds
-topset beds
-bottomset beds

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stream valleys

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most common landform on Earth's surface

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narrow valleys

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-V shaped
-downcutting toward base level
-features often include rapids and waterfalls

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wide valleys

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-stream near base level
-downward erosion is less dominant
-stream energy is directed from side to side forming a flood plain

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incised meanders

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meanders in steep, narrow valleys
-caused by drop in base level or uplift of region

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terraces

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remnants of a former floodplain
-river has adjusted to relative drop in base level by downcutting

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drainage networks

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land area that contributes water to the stream in the drainage basin
-imaginary line seperating one basin from another is a divide

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drainage pattern

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patter of the interconnected network of streams in an area
-dendritic
-radial
-rectangular
-trellis

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stream piracy

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the diversion of the drainage of one stream into another

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water gap

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notch were a river cuts through a ride that lies in its path

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antecedent stream

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stream existed before the ridge was formed

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superposed stream

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stream let down upon a preexisting structure

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types of floods

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-regional
-flash
-ice jam
-dam failure