Midterm 2 review

Catastrophes

damages to people/property whose impact will cause a long recovery time

How is risk determined?

potential consequences multiplied by hazard potential

Prediction

Specifying date, time, and size

Forecasting

include range of certainty (likelihood of future events)

Risk

probability of event * consequences

Hurricane Katrina catastrophe?

1. Failure of their levee system → poor design, construction and maintenance → flooding

2. Loss of freshwater wetlands (natural protection against flooding) + land subsidence

5 Fundamental principles

1. Hazards are known from scientific evaluation

2. Risk analysis is important in understanding impacts resulting from hazards

3. Hazards are linked

4. Hazardous events that previously produced disasters are now producing catastrophes

5. Consequences of hazards can be minimized

Magnitude

• energy released

• one value

• Richter or moment magnitude scale

Intensity

• observed effects and damage

• varies by location

• Modified mercalli intensity scale (MMI)

Modified mercalli intensity scale

• intensity

• measures shaking

• based on observed damage (1-7)

Moment Magnitude Scale

• replaced richter scale

• total energy released

• calculates seismic movement (fault displacement)

richter scale

• amplitude of seismic waves

• seismograph

• one whole number increase = 10x stronger

Ring of Fire

80% of Earth’s seismic energy is released along the earthquake zone around the Pacific rim

Earthquake concentration

Most earthquakes are concentrated along plate boundaries

strike

direction parallel to fault (relative to North)

dip

direction and slope of fault plane

moment

measured earthquake size

focus

place where earthquake originates

epicenter

point on surface of earthquake

what influences wave height?

fetch, duration, and velocity

types of currents

littoral

• longshore drift

• transport sediments along coastline

rip

• large waves crash to shore + rapid backflow

updrift

direction sand is coming from

downdrift

direction sand is going

refraction

waves converge at headland

diverge at embayment

factors of erosion that shapes coastlines

sand supply

severe storms

rise in sea level

human interference

manage coastal erosion

artificial barriers

groins

trap sand

act as barriers to longshore currents

con: down drift erosion - beach narrowing

breakwaters

protect shores from wave erosion

pro: stabilize shoreline, sediment accumulation

con: downdrift erosion, construction damage

jetties

stabilize channels to minimize deposition

con: disrupt natural flow of water, erosion

beach nourishment

adding sand to account for erosion, natural approach

con: so costly

hard engineering

man-made

seawalls, breakwaters, etc

soft engineering

beach nourishment

magnitude and timing of tides

• axial tilt

• geometry of basins

• air pressuree

what causes waves

wind blows across surface of water - friction ripples water

wave base

water depth below wave motion becomes negligible (low motion)

• half of the wavelength

what causes waves to break

seabed friction slows the base as it approaches shore

Loads streams carry

dissolved, suspended, and bed load

eorison or deposition may dominate based on stream velocity

dissolved load

ions from mineral weathering

suspended load

fine particles (silt + clay) in the flow

bed load (saltation)

larger particles roll, slide, and bounce

stream flow calculation

discharge : Q = A * V

stream base level

• lowest level that a stream erodes (usually sea level)

• ability based on velocity of water

  • velocity is proportional to slope

local (lake) vs regional (ocean) base level

base level lowering

steeper profile

increased stream erosion

• drops sea level, subsidence @ mouth, uplift head of stream, drains lakes

base level rising

shallower profile

deposit sediment

• sea level rise

• uplift @ mouth

• subsidence @ head

• creation of lakes

competence

max size particle transported

capacity

max load transported

discharge

volume of flowing water

runoff

water moving over surface as overland flow

vegetation influence on runoff

intercept precipitation

increase soil infiltration

reduce soil erosion

slow water flow

infiltration

water seeping into soil

stream origin points

• rain + water runoff

• springs/lakes

• snow melt

stream

body of water that flows in a channel; rivers are large streams

why do streams move in landscapes

• gravity

• erosion and deposition

oxbow lakes

form when a meandering river cuts off one of its bends, creating a standalone lake

hydrograph

graph of stream discharge over time

lag time between peak rainfall and discharge

urban development effects on hydrographs

shortens lag time

increase runoff, decrease filtration

sediment in streams

natural levees build after many floods

natural barriers for streams

evapotranspiration

water is transferred from the land to atmosphere from soil and plant leaves + stems