Natural Disasters (FDSCI 201) Exam 3

Landslide

A general term used to describe the downslope movement of soil, rock, and organic materials under the effects of water

Mass wasting, mass movement, slope failure

interchangable term for landslide

Gravity

The force that drives all mass movement

Friction and internal strength

The way materials are held into place that resist gravity and shear...

Angle of Repose

34 degrees which is the maximum angle of sand, little steeper than a 2:1 gradient

Moist sand

more stable than dry sand

Surface Tension

The small stength that the surface of a liquid has

Saturated

Completely full of water

What causes landslides?

Water: Slope saturation by water, caused by heavy rain or rapid snow melt. Earthquakes, Volcanoes

Landslide Dams

Landslides can cause flooding by forming landslide dams

Primary cause of landslides

Slope saturation

Most devastating landslides are caused by

Volcanic activity

human activities that cause landslides:

Destabilizing slopes, Changing drainage patterns, removing vegetation

Factors that make landslides more likely:

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

Landslide caused by a weak clay layer

Saint-Jude Landslide

Landslide caused by slope saturation

Puerto Rico Landslide

Common masswasting event due to volcanoes:

Lahars

Landslides occur in...

Every state and U.S territory

Areas that are prone to landslides

Steep slopes, old landslides, on or at base of slopes, in or at base of minor drainage hollows, at the base or top of slope, developed hillsides where leach fill septic systems are used

Areas that are safe from landslides

Hard unfractured bedrock, flat areas away from sudden changes in slope angle, top or along the nose of ridges away from tops of slopes

How much money do landslides cause in damage in U.S per year?

Excess of $1 billion

How many deaths in U.S from landslides each year?

25 to 50

Rock

Refers to hard or firm bedrock that was intact and in place prior to slope movement

Soil

Unconsolidated particles or poorly cemented rock or gravel

Debris

Coarse rocks

Earth

Fine grains

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 Slides

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

Transitional Slides

During these 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, vicous 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 movements occur sequentially and composite if they do not

Creep

Extremely slow movement

Avalanche

Extremely rapid movement

Rockfall

A mass of rock detaches from a steep slope by sliding, spreading, or toppling and descends mainly through the air by faliing, bouncing or rolling. Intenses rain, earthquakes or freeze-thaw wedging may trigger this type of movement

Rock Avalanche

A rockfall that moves rapidly

Rockslide

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

Slump

Rotational slide, can be identified by curved scarps and terraces at their heads

Debris Flow

Soil flow in which the majority of the materials are coarse-grained and non-cohesive

Debris Chute

A very steep path that has been stripped of vegetation from previous debris flows

Debris Fan

Successive debris flows that deposit material in the same area, which resembles a small steep alluvial fan

Mudflow

A mass of fine-grained soil that moves as a fluid, more watery than earthflows

Earthflow

A specific type of soil flow landslide where the majority of the soil materials are fine grained and cohesive

Cliff Retreat

Process of erosion that undercuts a cliff, thereby causing it to collapse and shift location away from erosion. A hazard wherever water comes into contact with cliffs.

Accretion

Ocean floor materials are scraped off the subducting slab during subduction

Melange

A mixture of materials that become part of the overriding continental crust

Stabilization

The general principal behind the landslide mitigation

Landslide mitigation measures:

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

Landslide warning signs

Areas that have not been wet before, new cracks, soil moving away foundations, decks and patio tilting

Final sign of a landslide

A faint rumbling sound that increases in volume

What a homeowner can do to mitigate landslides

Avoid destabilizing of slopes, Avoid water-related problems, get educated

What to do during a landslide (flood?)

Stay alert and awake, consider evacuating, listen carefully, be especially careful around rivers, turn around and dont drown, be aware of aftershocks

What to do after a landslide

Stay away, be aware, help, prevent

Floods

Most likely to be impacted by, coast to coast threat to US and all territories in all months of year. 3/4 of all presidential disaster declarations are associated with flooding

Most common cause of flooding:

water from rain or snow melt that accumulates faster than soils can absorb it or rivers can carry it away

Flood Monitoring

NOAA monitors conditions leading to flood 24/7 by measuring soil moisture and type

Flash flooding

Occurs when intense rains fall faster than the ground can absorb it

How much water can float a car

As little as 2 feet, avoid water... turn around dont drown

Minor Flooding

Minimal or no property damage, but possibly some public threat or inconvenience.

Moderate Flooding

Some inundation of structures and roads near streams. Some evacuations of people and/or transfer of property to higher elevations are necessary.

Major Flooding

Extensive inundation of structures and roads. Significant evacuations of people and/or transfer of property to higher elevations.

Storm surges

Generated by intense winds that push water inland, can exceed 20 feet

Ice Jam Floods

Rivers clog with ice rise rapidly due to rainfall or snowmelt and then the ice breaks up into chunks

Structural failure

Flooding can be caused by dam breaks or levee failures, resulting in a sudden release of water

Slot canyons

Can be death traps because water falling miles away can surge through them with ferocious power with little warning

Alluvial Fan

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

Meandering rivers

River traveling across flat land that wanders back and forth across the flood plain. Slow moving spread out flood

Channel

A path that a river normally flows in

Hydrologic Floodplain

A wider depression filled during seasonal high water, typically has many meanders and oxbow lakes in it

Topographic Floodplain

meandering river is defined by a significant rise in topography beyond the extent of the meanders. Formed over centuries by repeated flooding and erosion, marks the typical maximum of large floods

Braided Rivers

A river is choked with more sediment than it can carry, becomes divided into many branches.

Mountain Streams

Steep and fast flowing therefore can be very damaging floods by carrying large rocks during a fast flood

Drainage Basin

Geographic area that drives into a river

The biggest drainage basin in North America

Mississippi river

Flood stage

The depth of water at which a river flows over its banks, 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

Volume of water that flows by an established point in a period of time, measured in cubic feet per second

Hydrograph

A chart of river discharge over time

100 year flood

Biggest one that happened only once in the past 100 years (1% chance of happening each year but statistically irrelevant)

Flood Mitigation

Dams, Levees, Channel modification, Rip Rap

Dams

A space where water can accumulate can be effective but poses hazards when flood waters exceed reservoirs capacity

Levees

Barriers composed of sediments made on either side of a river due to flooding. Drawbacks include constant failure and backups worsening floods

Channel Modification

Removing brush and trees, deepening & widening the channel, change the channel to a more favorable route or location

Rip Rap

Stone placed on a slope to prevent erosion

The role of urbanization

Less water can soak into soil because covered by concrete and other things

The role of sedimentation

Floods can carry and deposit tremendous amount of sediment making recovery and mitigation of future flooding more difficult

Caliche

natural cement formed in desert soils when water evaporates

Atmospheric rivers

(aka Pineapple express)—a narrow band of intense atmospheric moisture that travels from the tropical Pacific thousands of miles to slam into the west coast of North America. They can carry 10-15x more water than the Mississippi, and deliver intense storms (rain and snow) to California.

Thistle, Utah 1983

Record setting rain and rapid snow melt caused many landslides in utah

$400 million, most expensive landslide in US

Destroyed the tiny town but more importantly destroyed highway and railroad

Yungay, Peru 1970

Earthquake caused rock avalanche to hit glacier turned into debris avalanche

25000 people killed, deadliest single landslide

May 31 is now a national disaster preparation and reflection day

Frank, Alberta 1903

Caused by ice wedging, freeze and thaw

70 people died

Monitored today by several instruments

Oso, Washington 2014

Caused by river had undercut hillside and heavy rain

Americas deadliest landslide 43 killed

Slump became a rapid mudflow

State settled before lawsuit went to trial

Mitigation: area has no homes

LaConchita, California 2005

Sea cliffs of weak material became saturated by heavy rain

Previous mudflow 1995 reactivated

10 people killed, including family of Jimmy wallet

Homes should never have been built there

Put up a warning sign but really no mitigation efforts

Happened during an atmospheric river (pineapple express)

Vaiont Dam Disaster, Italy 1963

Newly built europes highest dam (800 ft) caused landslide

Landslide 1.5 miles wide fell into reservoir pushing water over dam

Dam did not fail, is still there

killed 2500, including 800 children

Caused by high pore pressure weakened bedrock in submerged cliff walls, tilted shale layer allowed sliding

Haiyuan, China 1920

M8 earthquake Dec 16 triggerd > 200 landslides in soft loess (windblown) soil

Over 200,000 killed, about half in landslides

Mudflows, debris flows, slumps

Shallow quake had mercalli intensity XII

Landslides blocked rivers, creating dams and floods, several buried cities

Lituya Bay, Alaska 1958

July 9

earthquake triggered massive rockfall, which landed in bay

Highest tsunami ever recored, 1700 ft

traveled down the bay and out to the ocean

Father-son fisherman road over wave in boat, 5 others killed