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1
Natural Hazards 2
„Nature to be commanded, must be obeyed“ (Francis Bacon, 1561-1626)
W. Eberhard Falck [email protected]
2
Natural Processes
3
Driving forces behind natural processes
• There are three fundamental phenomena that drive all natural processes:
– radioactive decay – gravity – the Earth‘s rotational inertia
• They cause/drive mass and energy flows throughout the natural environment
• Neither of these processes can be stopped or controlled by us humans
4
Radioactive decay in the environment
• It ‚powers‘ the sun
• Solar radiation causes the movements in the atmosphere (= wind) due to differential heating of different surfaces (e.g. water, land)
• Solar radiation causes evaporation and (indirectly) evapotranspiration from plants
5
Radioactive decay and geology
• It keeps the Earth‘s interior hot
• Without the decay heat, the Earth would have cooled down in about 30,000 years (Lord Kelvin)
• The heat flow from the earths drives phenomena such as
– vulcanism - earthquakes
– plate tectonics - orographic changes
6
Gravity
• Drives the surface water flow from the mountains to the sea
• Drives the groundwater flow (pressure differences due to different elevation)
• Causes eroded material to move downwards
• ‚Mountains‘ are a higher degree of order - according to the 2nd law of thermodynamics this order will dissipate
7
Rotational Inertia
• Causes, together with gravity, the tidal waves in the oceans
8
Overview: Natural Hazards
9
Hazard classification by root cause
• Endogenic – having their root in processeses in the Earth‘s interior
• Exogenic – having their root in processes above ground
• Extraterrestrial – e.g. meteorite impacts
10
Normal processes vs. catastrophic events
• Many exogenic, e.g. weather-related, processes occur regularly and do not pose any hazards
• Changes in intensity, in timing or co-occurence of several phenomena can lead to catastrophic events
– heavy rainfall after a long dry seasons can lead to flooding or mud-slides
– heavy rainfall in several different regions of the same catchment area can lead to flooding
– prolonged wet weather can lead to mud-slides
• Normal events can trigger chains of events that finally lead to catastrophic events
11
Endogenic hazards
• earthquakes
• volcanic phenomena
• tsunamis
• eustasis related phenomena
• natural radioactivity
12
Exogenic hazards
• particularly relevant in high-energy environments – mountain areas – coastal areas – river valleys – because of
• high relief energy, i.e. steep slopes, altitude differences • lack of protection from wind, waves etc. • tidal forces
• climatic changes/variations – natural or human induced – change the dynamic equilibria in nature – humans have arranged themselves with a particular state of
nature, which is changing later
13
Weather-related hazards
• storms
• heavy rainfall
• hail
• snow
• severe frost
• severe heat
• droughts
14
Water-related hazards
• inundations
• (flash)floods
• avalanches
• tidal phenomena
• rogue ocean waves
15
Geology-related hazards
• torrents
• mud flows
• rock falls
• landslides
• cave-ins
• permafrost-related
16
Extraterrestrial hazards
• magnetic storms
• meteorite impacts
17
Endogenic hazards
18
Earthquakes
19
Causes • The Earth‘s crust is made up of numerous plates that slowly
move due to convections in the mantle
• Slow movements occur along other fault zones in the crust
• The frictional energy built up is released spasmodically - an earthquake
• Small earthquakes can also occur due to volcanic activity
• Sometime earthquakes have an anthropogenic origin: e.g. collapsing underground mines
• Large earthquakes occur about once a year
• Small earthquakes occur about once an hour
20
Plate tectonics
21
Tectonic plates
22
Tectonic plates: animation
23
Global distribution of earthquakes
24
Phenomenology • Earthquakes generate different types of waves
• The strength and characteristics of these waves can be recorded by seismographs
• From these measurements their location, the focus and the epicentre, can be determined
• The strength of an earthquake can be measured by magnitude and intensity
• The Richter scale measures the energy of the seismic waves (open logarithmic scale)
• The Mercalli scale measures the intensity or effect on the surface of the earth (descriptive scale)
25
Mercalli vs.Richter Scale
26
Seismographs and seismograms • The seismograph utilises the inertia of a mass (e.g. a heavy
metal ball) relative to the moving ground
27
Earthquake hazards Direct hazards • Total or partial collapse of structures • Falling debris and dust from rubble • Transportation casualties due to collapse of bridges etc. • Floods from collapsed dams or river banks • Landslides and soil liquefaction • Tsunamies
Indirect Hazards • Fires • Release of hazardous material • Electrocution • Exacerbation of pre-existing hazardous situations
28
Earthquake impacts • Total or partial
destruction of structures • Blockage or interruption
of transport systems • Interruption of water, gas
and electricity supplies • Breakage of sewage
systems • Interruption of land-use
due to landslides or inundation
29
Can they be predicted ?
• Science cannot yet predict earthquakes as to time or location of their occurrence
• We can only predict probabilities for regions and time spans
• For instance, the United States Geological Survey (USGS) calculates a probability of 67% for a major earthquake to occur in the San Francisco area within the next 30 years
• Research to understand possible warning signals is ongoing
• ‚Urban myths‘: – Earthquake weather/season
– Animals or certain people can sense an oncoming earthquake
30
Mitigation measures
• Measures and strategies to mitigate the effects and impacts
• Earthquake resistant buildings/ infrastructure
– Lightweight construction – Cross-bracing – Decoupling – High-strength door-frames – Brick buildings are
unsuitable • Emergency preparedness • Behavioural advice, e.g.
„drop-cover-hold on“ (USA)
31
Emergency preparedness
32
Earthquakes - socio-economic impact After the event • Desaster relief costs • Lost economic opportunities • Loss of land-use due to landslides etc. • Cost of rebuilding houses and infrastructure • Disruption of societies • Health impacts due to traumatisation and poorer healthcare
Precautionary measures • Emergency preparedness costs • Higher cost of safer building practices / retrofitting • People / companies avoid earthquake zones - lost
employment / economic opportunities
33
Volcanoes
34
What is a volcano ? • An opening, or rupture, in the Earth's crust that allows hot
magma, ash and gases to escape from below the surface • Volcanoes occur
– along plate boundaries – above mantle plumes (hot spots) within plates – as non-hotspot intraplate volcanism where a thinning of the Earth‘s
crust occurs
35
Typical occurence of volcanoes
36
The classical volcano: Stratovolcano
• Examples are Vesuvius, Aetna, Stromboli, Fuji
37
Volcano hazards
38
Arctic Vulcanos
• Sub-glacial vulcanos can pose the added risk of causing glacier surges, e.g. on Iceland
39
Volcanic eruption impacts • Earthquakes • Lava/mud flows destroy houses /
infrastructure • Pyroclastic flows (up to 700 km/h, 1000°C)
cannot be escaped • Volcanic bombs • Ash rain suffocates animal and plant life • Large-scale eruptions eject ash into the
strathosphere, where it can circulate for years and change the global climate (e.g. Krakatau, 1883)
• Tsunamis • Poisonous and/or suffocating exhalations
(H2S, SO2, CO2) • Aerosols causing health problems • Acid precipitation • Glacier surges and melt-water torrents
40
Forecasting volcanic activities
• Most volcanoes (on land) and zones with volcanic activity are well known
• These zones are monitored
• Monitoring for seismic activity
• Precision geodesy to detect surface distortions
• Monitoring of effluent gas composition
• However, predicting the precise period for an eruption is difficult with the risk of false alarms or too late evacuation
41
Volcanic risk mitigation
• Mapping of hazard/danger zones
• Land-use restriction in danger zones
• Emergency preparedness plans
• Monitoring seismic/volcanic activities
• Evacuation when eruptions are iminent
42
Mapping hazard zones
43
Socio-economic impacts • Cost of mitigation measures • Cost of emergency relief operations • Cost of re-building houses and infrastructure • Cost of reforestation • Cost of slope stabilisation measures • Loss of farmland • Exacerbated health problems due to poorer healh care and
exposure to health hazards (e.g. dust) • Disruption of economic activities (e.g. the Philipine GDP fell by
3% in the years after the Mt. Pinatubo eruption) • Disruption of social life • But also benefits, such as geothermal energy on Iceland
44
Tsunamis
45
The Japan tsunami on 11 March 2011
46
The Japan tsunami on 11 March 2011
47
What is a tsunami ?
48
Mechanisms of tsunami generation
• Displacement of rock masses cause displacement of water
• Root causes can be – earthquakes, – seabed slides – volcanic eruptions – cliff collapse – iceberg calving
Before the earthquake
Earthquake
Tsunami spreads out
49
The travel of the tsunami of 26/12/2004
50
Tsunami early warning systems • Following the tsunami that hit various regions around the Indian
Ocean on 26/12/2004, the efforts to set up early warning systems were considerably intensified.
• Early warning systems integrate the world-wide network of seismic stations with oceanic observation stations
• Like earthquakes, tsunamis cannot be predicted, but there are often several hours before a tsunami hits a coast and its spreading can be predicted
51
Tsunami emergency preparedness
52
Tsunami risk maps
53
Socio-economic impacts • Cost of mitigation measures • Cost of emergency relief operations • Cost of re-building houses and
infrastructure • Cost of re-building coastal
infrastructure • Loss of fishing grounds and
infrastructure, e.g. fishfarms • Exacerbated health problems
due to poorer healh care • Disruption of economic activities • Disruption of social life
54
Isostatic processes
55
Definition
• Can have endogenic and/or exogenic causes
• A collection of processes that result in changes of the mean sea level
• The mean sea level depends on the volume of the oceanic water
• The mean sea level depends on the topography of the ocean floors
• The topography of the ocean floors has changed significantly over geological timescales
• Isostatic rebound following the ice-age is a major mechanism e.g. in Northern Europe
56
Mean sea level
• Local mean sea level (LMSL) is defined as the height of the sea with respect to a land benchmark, averaged over a period of time (such as a month or a year) long enough that fluctuations caused by waves and tides are smoothed out
57
Isostatic rebound
• The continental crust floats on top of the mantle • Changes in load on the continents results in variations in
‚draft‘ and dipping • The appearance and retreat of continental ice sheets are such
a change in load
before glaciation during glaciation after glaciation
58
Large-scale uplift of continents
• In some areas accompanied by subsidence of neighbouring areas
• For instance, The Netherlands are sinking
59
Hazards and impacts • Slow, long-term movements in the order of 0.1 to 10 mm/year
• Rising areas: – Receding coastline – Drying-up of harbours
• Subsidence areas: – Increasing probability of flooding – Increase of coastal erosion – Need to improve coastal defence measures – Considerable socio-economic impact e.g. in the
Netherlands – Salination of near-coast groundwaters
60
Next lesson
• Natural radioactivity • Exogenic hazards