Natural Disasters Final

Flash Floods

arises quickly, short intense rainfall. Take more lives than any other flooding.

River flooding

runoff from rain events flow into rivers and streams faster than the water moves downstream, and causes flooding.

Tropical Cyclones

effects of extreme winds and coastal storm surges. Rainfall is typically heavier and slower moving storms allow it to continue falling.

Coastal flooding

winds with hurricanes cause storm surges

Snow melt floods

warm conditions and heavy rain can combine with snow melt which causes extensive flooding, but it can happen alone

Ice Jam Floods

when rivers clog with ice rise rapidly due to rainfall or snowmelt, ice breaks into chunks and can jam, causing water to back up

Mudflows

Moderate amounts of rain can cause mudflows on burned hill slopes

Slot canyons

formed over centuries by water eroding narrow slits into sandstone.

Alluvial Fan

fan-shaped apron of gravel deposited by flash floods and debris flows at the mouth of a canyon.

Meandering rivers

when a river travels across flat land, wanders back and forth.

Oxbow lakes

as the bends in meandering rivers migrate, they cut each other off forming these lakes

Point bars

at the inside of the bend of meandering rivers, these form as sand and gravel get out of the rapid flow and are deposited. It grows at the same time the outside bend grows, so the river channel shifts

Channel

the path that a river normally flows in

Hydrologic floodplain

this wider depression is filled during seasonal high water. Typically has many meanders and oxbow lakes.

Topographic floodplain

formed over centuries by repeated flooding and erosion, marks the typical maximum of large floods. Defined by a significant rise in topography

Braided Rivers

when a river is chocked with more sediment than it can carry, it becomes divided into many branches. Fast moving- cause more erosion and structural damage

Mountain streams

steep and fast-flowing, can carry large rocks and erode surrounding valley sediments

Drainage Basin

the geographic area that drains into a river- Mississippi river has the biggest drainage basin in North America

Flood stage

the depth of water at which a river flows over its backs, potentially causing property damage

Flood gage

an instrument that uses sensors to measure the height (called stage) of river water above the river channel bottom.

Staff gage

a big ruler used for visual check of river stage, and is also measured from the bottom of the river channel

Discharge

the volume of water that flows by an established point in a period of time, typically measures in cubic feet per second. Formula- cross-sectional area of the river channel times flow velocity

100 Year flood

the highest flood of the past 100 years, or if that is not available, a statistical projection of what that flood might be.

Dams

cause profound changes to river systems by stopping the flow of sediment downstream, changing local habitats for fish and wildlife, and stopping fish migration- so not built as regularly as in the past

Levees

berms or walls built to contain a river or other water body. we can build them wherever needed, but they can fail- they also can create a bottle neck or narrow passage that causes the river to back up, increasing the severity of the flood

Channel modification

removing brush and trees, deepening and widening the channel, and changing the channel to a more favorable route or location

Rip-Rap

blanket of boulder size rocks designed to prevent erosion at strategic locations-must be large enough that the flood waters cannot move them

Caliche

natural cement that forms on desert soils when water evaporates, leaving behind its mineral content-major reason for flash-floods

Role of Climate and Landscape

soils in wet climates have high capacity to absorb water, while soils in desert climates do not

“The Pineapple express”

pulls moisture from around Hawaii, causes heavy flooding in California, and other surrounding states

landslide

downslope movement of soil, rock, and organic materials under the effects of gravity

force

that drives all mass movement is gravity

angle of repose

34 degrees for dry sand, little steeper than a 2:1 gradient (2 feet horizontally for every 1 foot up)

water (natural cause)

slope material that became saturated with water may develop a debris flow or mud flow

earthquakes (natural cause)

in steep landslide prone areas increase risk of a landslide

Volcanoes (natural cause)

may melt snow at a rapid rate, can accelerate a landslide

Slope saturation

by water, primary cause of landslide. causes slope to loose strength. -heavy rain or rapid snow melt. -changes in ground-water levels, water-level changes along the banks and shores of bodies of water

Landslide dams

landslides can cause flooding by forming landslide dams that block valleys and stream channels, allowing large amounts of water to back up.

Landslides and Volcanoes

most devastating types

Destabilizing of slopes by humans occur by:

grading or excavation that removes material from the base and loads material at the top, undercutting the bottom of a slope, loading the top of a slope to exceed bearing strength, and disturbing and re-activating old landslides

changing drainage patterns occurs by:

addition of water to a slope, roof downspouts, poor drainage, septic-tank effluent, canal leakage, broken water or sewer lines, draining of reservoirs, and improper excavating or grading on slopes

Removing vegetation occurs by:

fire, deforestation, land development

Factors that make landslides more likely:

weak materials, steep slopes, lack of vegetation, climate, tilted layers, clay layers

rate of movement

rapid to slow

type of material

either rock or soil, or combination of the two

type of movement

falling, toppling, sliding, spreading, or flowing

Falls

masses of soil or rock that dislodge from steep slopes and free-fall, bounce, or roll downslope

Topples

move by the forward pivoting of a mass around its base

slides

displace masses of material along one or more discrete planes and are grouped by the way they move: rotational and translational

Rotational slide

during these slides, the slide plane is curved and the mass rotates backwards around an axis parallel to the slope

Translational

during the slides, the failure surface is more or less planar and the mass moves parallel to the ground surface

Lateral spreads

commonly induced by liquefaction of material in an earthquake, move by horizontal extension, shear or fractures

Flows

mobilize as a deforming, viscous mass without a discrete failure plane

Combinations

more than one form of movement may occur during a failure, in which case the movement is classified as complex if movement occur sequentially and composite if they do not

Most common material combinations:

rockfalls, rockslides, slump, debris flows, mud flows, earth flows, creep, and cliff retreat

rockfall

type of mass movement in which a mass of rock detaches from a steep slope by sliding, spreading, or toppling and descends mainly through the air by falling, bouncing, or rolling

Rock avalanche

a rockfall that moves very rapidly in this way: severe dust clouds, airborne projectiles, air blasts

Rockslide

a landslide involving bedrock in which the rock that remains largely intact for at least a portion of the movement

Slump

rotational slide-curved scarps and terraces at their heads

Debris Flow

soil flow in which the majority of the materials are coarse-grained-most triggered by intense rainfall, or rapid snow melt

Mudflow

mass of fine-grained soil that moves as a fluid mass-prolonged rainfall

Earthflow

specific type of soil flow landslide where the majority of the soil materials are fine-grained and cohesive -slow moving

Creep

imperceptibly slow movement of soil or rock, result of the freeze thaw cycle.

cliff retreat

process of erosion that undercuts a cliff, thereby causing it to collapse and shift location away from the erosion- hazard wherever water comes in contact with cliffs -3 feet per year

What plate was the west coast of the U.S.?

Convergent plate

Melange

during subduction, ocean floor materials are scraped off the subducting slab. these materials become part of the ocer-riding continental crust. Melange forms a characteristic landscape of low hills, common landslides, and isolated pieces of hard rock. -rich in clay and thoroughly sheared.

Landslide mitigation:

slope reduction, surface and subsurface drainage, terracing and rock walls, plants with deep root systems, buttressing: putting a heavy rock blanket on a soft slope

Risk

product of the extent, effects, probability, and importance of the outcome

Disaster

natural emergency whose response needs are great

Hazard

hazardous condition that exists may not have even happened yet

Exposure

how many people/buildings are in the way of the hazard

Probablility

likelihood of a specific type of event occurring in a specific place

Mitigation

activities to reduce losses from disasters including prevention and protection. Increase response capability. Alter, avert, adapt, avoid

Plate

large, rigid slab of solid rock made of crust and the top of the mantle

Tectonics

"to Build" earth's surface is built of plates

Theory of plate tectonics

Earth's outmost layer is fragmented into a dozen or more large and small plates that are moving relative to one another

Catastrophism

biblical flood played a major role in shaping the Earth's surface- all earthly changes were sudden and caused by a series of catastophes

Uniformitarianism

19th century- the present is the key to the past -geological forces and processes acting on the Earth today are the same as those that have acted in the geologic past

Continental Drift

Pangea, continents broke apart fatal weakness

Fundamental Difference

explanations of the role of the seafloor crust

4 scientific Developments

1) Demonstration of ruggedness and youth of ocean floor

2) Confirmation of repeated reversals of Earth's magnetic field in geologic past

3) Development of sea-floor spreading hypothesis and associated recycling of oceanic crust

4) Precise documentation that the world's earthquake and volcanic activity is concentrated along oceanic trenches and submarine mountain ranges

Mid-Atlantic Ridge

submarine mountain chain in central atlantic

Global Mid-Ocean Range

immense submarine mountain chain

Normal Polarity

characterized by magnetic minerals in rock having the same polarity as the Earth's present magnetic field

Reversed Polarity

polarity alignment opposite to that of the Earth's present magnetic field

Alfred Wegner

Pangea- German meteorologist- continental drift

Seafloor spreading

ocean floor ripped in 2 lengthwise, new magma from within Earth rises easily through the weak zones and erupts along crest of ridges to create new oceanic crust

Magnetic striping

in lava, grains of magnetic like magnets can align themselves with orientation of Earth's magnetic field- when magma cools, alignment of magnetic grains "locked in" recording the Earth's magnetic orientation or polarity

Convergent Boundaries

crust is destroyed as one plate dives under another -explosive volcanism and strong earthquakes -reverse/thrust faults

Divergent boundaries

new crust is generated as plates pull away from each other -oceans and volcanos -normal faults -moderate shallow quakes

Transform boundaries

where crust is neither produced nor destroyed as plates slide horizontally past each other -San Andreas -strike-slip faults

Subduction Zones

earthquakes concentrated in very specific narrow zones

Plate boundary zones

broad belts in which boundaries are not well defined and effects of plot interaction are unclear

Spreading Centers

divergent boundaries occur where plates are moving apart, and new crust is created by magma rising up from the mantle

Global mid-ocean ridge system

encircles the earth

Normal fault

any fault at which rock above the fault moves downward resulting in extension and common wherever crust is extending -divergent plate boudaries

Iceland

Volcanic country -straddles Mid-atlantic range