Hazards

Natural hazard

A perceived event that threatens both life and property

Natural disaster

A hazard becoming reality leading to damage and casualties

Type of natural hazard - Geophysical

Driven by the Earth’s own internal energy sources - plate tectonics, volcanoes and seismic activity

Types of natural hazard - Hydrological

Driven by bodies of water, mainly the oceans - floods, storm surges and tsunamis

Types of natural hazard - Atmospheric

Driven by the processes at work in the atmosphere - droughts and tropical storms

Characteristics of hazards

Clear origins and distinctive effects - short warning time - involuntary exposure to risk - scale and intensity require emergency response - most damage / death occurs shortly after the event

Reasons why people put themselves at risk

Hazards are unpredictable - not perceive it as dangerous - advantages outweigh the risks - lack of suitable alternatives - changing level of risk

Perception of natural hazards - Fear

People feel so vulnerable to an event that they are no longer able to face living in the area

Perception of natural hazards - Fatalism

Hazards are natural events (part of ‘Gods will’) so action will be direct and focussed on safety - losses are accepted as inevitable

Perception of natural hazards - Adaptation

People see that they can prepare for an survive the event by prediction, prevention and / or protection

Primary effect

Effects that result directly from the hazard event

Secondary effect

Effect that result from the primary effects

Example primary effect

Destruction of buildings, crustal fracturing

Example of secondary effect

Tsunami, liquefaction, disease, landslides, death from hypothermia

Liquefaction

Solid ground takes on the properties of liquid usually after an earthquake

Prediction

Warnings given before a hazard happens, allowing people to prepare and evacuate to safety

Protection

Protect people and the built environment

Prevention

Unrealistic with most hazards but some theories and ideas on possible methods

Community preparedness

Pre-arranged measures that aim to reduce loss of life and property damage through public education and awareness programmes, evacuation procedures, provision of emergency medical, food supplies and shelters

Hazard management cycle

Cycle which shows how to manage the complete lifespan of a hazard - before, during and after

The Park Model

Shows how a country or region might respond after a hazard event - can be used to directly compare how areas of different levels of development might recover

Issues with the Park Model

Too generalised, no account for further hazards, no spacial variations

Alfred Wegener

Creator of the Plate Tectonic Theory / continental drift

Plate Tectonic Theory / Continental Drift

The gradual movement of the continents across the earth’s surface through geological time

Slab Pull

The subducted plate is pulled further down due to gravity

Ridge push

Hardening of lava and gravity pushes the plates away from others

Oceanic Ridge

Constructive plate boundary - plate moves apart in oceanic areas - space is filled with basaltic lava - upwelling forms a ridge - submarine volcanoes may eventually rise to form islands - Surtsey

Island Arc

Subducted plates melt and rise towards the surface as plutons - form complex, composite and explosive volcanoes - eruptions that take place offshore for a ,one of volcanic islands

Deep Sea Trenches

Subduction of oceanic plates cause a very deep part of the ocean - can occur at all destructive subduction plate boundaries

Rift valleys

Formed on constructive plate boundaries in continental areas - parallel faults form when the lithosphere is stretched by heating and expansion caused by magma plumes- areas of crust fall down between the faults - left horsts behind

Young fold mountains

Little subduction happens when continental plates collide - edges are forced up into fold mountains with deep mountain roots

Oceanic plate meets continental plates

Destructive plate boundary - oceanic plate subducts - creates deep oceanic trenches and fold mountains - causes earthquakes and volcanoes - Nazca plate (oceanic) and South American plate (continental)

Oceanic plate meets oceanic plate

Destructive plate boundary - denser or faster plate subducts - creates volcanic island arcs and deep sea trenches - causes earthquakes and volcanoes - Mariana Trench and Marianas Islands

Continental plate meets continental plate

Destructive plate boundary - no subduction so plates crumple up - creates fold mountains - causes earthquakes - Himalayas caused by the Eurasian plate and Indian plate

Constructive plate in oceans

Regular breaks in each plate (transform faults) move at different speeds to one another - smaller sections of plate create conservative plate boundaries with one another - magma rises up into the gaps - creates mid ocean ridges - causes volcanoes and earthquakes - Mid Atlantic ridge

Constructive plate boundary on land

Lithosphere begins to stretch - plate fractures into sets of parallel faults - rift valleys drop down in between them with horsts staying in place - creates rift valleys - causes earthquakes and volcanoes - East Africa Great Rift Valley

Conservative plate boundary

Two plates slide past one another - friction may cause shallow earthquakes - causes earthquakes - San Andreas Fault

Magma plumes

Radioactive decay in the earths core causes high temperatures - heats the lower mantle creating localised thermal currents where magma plumes rise, if found in the middle of a plate, can burn through the lithosphere - creates volcanic activity on surface - plate moves but hotspot does not - forms a chain of active, then extinct volcanic islands - Hawaii

Fault webs

Latur Earthquake in 1993 - pressure held in plate boundary was released along the fault lines

VEI

Volcanic explosivity index - used to compare / describe the magnitude of volcanic eruptions between 0 - 8 - takes into account amount and height of material ejected, length of eruption and qualitative descriptive terms

Basaltic Lava

Hottest - low gas content - low viscosity to allow gases to escape - gentle eruption energy - least dangerous

Rhyolitic lava

Coolest lava - high gas content - high viscosity to trap gases - violent explosion - most dangerous

Icelandic Volcanoes

Basaltic Lava - least dangerous

Plinian volcanoes

Rhyolitic lava - most dangerous

Tephra

Solid material of varying grain size ranging from volcanic bombs to ash all ejected into the atmosphere

Pyroclastic flows

Nuèes ardentes - very hot, gas charged, high velocity flows of a mixture of gas and tephra

Lahars

Melted snow and ice as a result of the eruption combined with volcanic ash forms mud flows that can move at high speeds

Fissure eruptions

Creates extensive lava plateaus - fills in hollows in the land

Basic shield volcanoes

Shallow sided and broad - formed by basalt that cools as it runs down from the summit crater - gentle eruptions that can become tourist attractions

Acid dome volcanoes

Steep sided convex cones - thick lava - explosive eruptions with deadly impacts

Composite cones

Formed with alternating eruptions of ash, tephra and lava - mostly irregular due to the weaknesses in the walls

Calderas

Result from the violent eruptions that blows off the summit - volcano collapses in

Primary wave

Arrives first, fast, moves through solid risk and fluids - compresses in the direction of travel

Secondary wave

Slower than P wave, only moves through solid roc - up and down movement

Love wave

Only travels through the surface of the crust - horizontal movement

MMS

Moment magnitude scale - scales between 1 - 10 - scale is logarithmic

Modified Mercalli Intensity Scale

Takes observations from people who experienced the earthquake and rates them on a scale from I to XII

Prediction of earthquakes

Microquakes before the main event, bulging of the ground, decreasing radon gas concentrations in groundwater and curious animal behavior

Physical factors affecting earthquake impact

Magnitude, depth of hypocentre and distance from epicentre

Human factors affecting earthquake impact

Level of development, population density, level of preparedness, effectiveness of repose and time of day

Aftershocks

Smaller earthquakes after the original earthquake caused by the earth settling down or readjusting along the part of the fault line that originally slipped

Fault lubrication

Prevention - pumping water into fault lines to reduce friction - smaller less damaging earthquakes - water may not be available in all areas so not sustainable

Drilling boreholes

Prevention - soil properties are changed to reflect seismic waves - expensive

Tree planting

Prevention - trees planted with the tallest closest to the earthquake source to prevent them from reaching the city - sustainable but requires large areas

ShakeAlert

Prediction / early warning - detectors sense the

Tsunami

Generated by seismic activity on the sea floor - earthquake or volcano - large wavelength with high speed

Tsunami increases in wave height towards the shore

Friction causes the wave to slow down and increase in height - increases friction with distance to the shoreline - sea floor obstacles such as coral reefs can decrease the energy, decreasing the height

Natural warning sign of a tsunami

Water recedes from the coastline - not always present at all tsunamis

Formation of Tropical Storms

Ocean at 27°c - depth of 70m - low pressure - thunderstorm clouds - join together to make spinning storm with eye at centre - 74mph to become a hurricane

Movement of tropical storm

Carried across the ocean by prevailing wind - continues to gather strength due to the evaporating / condensing water

Cause of the eye of the storm

Cold air sinks in the eye, causing higher pressure and better conditions - drier and calmer with no cloud

Spread / location of tropical storms

5° - 30° north and south of the equator due to the temperature needed and cortisol is effect being strong

Why is there no tropical storms on the equator

Coriolis effect is not strong enough to force the clouds to spin

Importance of low wind shear for tropical storms

Allows for the clouds to rise without being ripped apart

Measurement of the magnitude of tropical storms

Saffir-Simpson scale - based on sustained wind speed of the storm - 5 categories

Strong winds

Caused by changes from high to low pressure as the pressure tries to balance out - property damage and transport disruptions

Storm surge

Caused by low air pressure and strong surface winds - pushes water up onto the coast higher than normally - property damage, saline intrusion, coastal erosion, drowning

How does low pressure help storm surges

Low pressure brought by tropical storm enables the sea to rise vertically

Coastal and river flooding

High rainfall and storm surges overwhelm rivers within drainage basin - property damage, severe infrastructure damage

Landslides

Surface of a slope fails and collapses down - caused by high rainfall which increases pore pressure and adds extra weight to the slope - infrastructure damage, environmental damage, death

Connection between landslides and earthquakes

Load release from tropical storm caused landslides has been linked to earthquakes in tectonically stressed regions - extra water lubricates the plate margin

Preventing tropical storms - cloud seeding

Silver iodine is injected into the atmosphere over the tropical storm - makes it rain before it hits the coast

Preventing tropical storms - Salter sink

Suck warm surface water down into deeper water, to be replaced with cold water below - reduces the surface temperature of the water

Preventing tropical storms - cloud brightening

Droplets of seawater are sprayed into the atmosphere to make clouds brighter - reflects more heat back into space to cool the surface

Preventing tropical storms - offshore wind farms

Offshore wind farms hinder and slow down the rotating winds in the outer part of the storm - reduces the height of the sea waves - causes a rise in atmospheric pressure - dissipates the hurricane faster

Prediction of tropical storms - satellites

Monitors precipitation between 65° north and south of the equator to identify high altitude clouds that are likely to turn into tropical storms

Prediction of tropical storms - aircraft

Specially equipped aircraft fly into tropical storms to collect data on air pressure, rainfall and wind speed

Mitigation of tropical storms - sea wall

Blocks any storm surges - may not be high enough for climate changed storms - Galveston Texas

Mitigation of tropical storms - mangroves

Natural barrier against storm surges and tsunamis

Mitigation of tropical storms - insurance

Guarantee that some financial reparations from storm damage - may be unaffordable for some people due to premiums

Adaptation to tropical storms - land zoning

Only allows for low value land uses close to the coast - properties are raised on stilts and have non residential functions

Adaptation to tropical storms - stilts

Raise up the house to reduce the risk of flood damage with non residential uses on the ground floor

Adaptation to tropical storms - income diversification

Used in LIC / NEE - fewer people are dependent on fishing or sectors that can easily be damaged by tropical storms

Adaptation to tropical storms - mangroves

Replant the mangroves to act as a buffer against storm surges