Lecture 11: Coastal Hazards

Question 1

Hazard does not always equal

Answer 1

risk

Question 2

Hazards are usually measured based on their…

Answer 2

frequency and magnitude

large events occur far less frequently than small events

Question 3

Risk =

Answer 3

H x E x V

(hazard x vulnerability x exposure)

Vulnerability and exposure can change over time

Question 4

Hazards happen in the absence of

Answer 4

humans

Question 5

Risk happens in the presence of

Answer 5

humans

Question 6

Exposure =

Answer 6

££ value of infrastructure or number of people within a coastal zone

Question 7

Vulnerability =

Answer 7

“susceptibility to harm”

Question 8

event-driven (episodic)

Answer 8

tsunamis
hurricanes, storms & cyclones
storm "clusters"
rip currents
rock fall (cliffs)

Question 9

chronic

Answer 9

shoreline erosion (sediment delivery)
nuisance flooding 
climate-related hazards (slow, very large-scale drivers)
relative sea-level rise
ocean acidification
ocean temperature
hypoxia (nutrient loading)

Question 10

What is a tsunami caused by fundamentally?

Answer 10

caused by water displacement usually at a tectonic boundary offshore (earthquake, lg landslide…).
An earthquake pushes up or drops down one part of the seafloor relative to another.
This displaces a volume of water, pushing it up.
Sets of an oscillation, which develops underwater at great speed.
Sea water is sucked back from the shore.
Waves get bigger as water gets shallower.

Question 11

What direction do cyclones turn in the northern hemisphere?

Answer 11

Anti-clockwise

Question 12

What direction do cyclones turn in the southern hemisphere?

Answer 12

Clockwise

Question 13

What is a tropical cyclone?

Answer 13

A rotating low-pressure weather system that has organized thunderstorms but no fronts (a boundary separating two air masses of different densities).

Question 14

tropical depression max sustained wind =

Answer 14

max sustained surface winds < 39 mph

Question 15

tropical storm max sustained wind =

Answer 15

maximum sustained winds of > 39 mph

Question 16

hurricane max sustained wind =

Answer 16

maximum sustained winds > 74 mph

Question 17

What is the Coriolis effect?

Answer 17

The Earth’s rotation means that we experience an apparent force known as the Coriolis force. This deflects the direction of the wind to the right in the northern hemisphere and to the left in the southern hemisphere.

Question 18

What is rip current?

Answer 18

An intermittent strong surface current flowing seaward from the shore.
A self organised feedback (in time and space)
Can also be geologically controlled

Question 19

How does a rip current form?

Answer 19

Rip starts (1) with slight difference in beach morphology (like a gap between sand bars) or a difference in wave forcing onshore

2) larger waves on either side of the incipient rip push farther up the beach creates a lateral gradient: at rip, less onshore forcing means easier for water to flow offshore…
(3) fed by gradient in flow, feedback strengthens if strong enough, can carve a channel in the beach (a “rip channel”)

Question 20

Why are rip currents temporary?

Answer 20

Rip is temporary because wave forcing tends to be variable and rip will die out if the flow gradient weakens enough

Question 21

climate-related (large, slow…)

Answer 21

relative sea-level rise (makes all other elevated water levels worse – e.g., trend!)
CO2 input
ocean acidification
ocean temperature
hypoxia (nutrient loading) – algal blooms that use up all available dissolved oxygen in nearshore waters