Natural Hazards and Society (ES5001) PDF

lOMoARcPSD|27413003 Large ditch or reinforced concrete wall can reduce impact of first wave Infrastructural adaptation and emergency planning; Hazard maps Resistant building design, warni...

lOMoARcPSD|27413003 Large ditch or reinforced concrete wall can reduce impact of first wave Infrastructural adaptation and emergency planning; Hazard maps Resistant building design, warning signs, vertical evacuation structures Awareness and emergency drills your first reaction should be to immediately head for a location as high above sea level as possible Tsunami warnings: Warning systems now perfected for far field (far from the source) tsunami Pacific Ocean tsunami warning network monitors large earthquakes and ocean waves and transmits warnings to 26 countries. Travel time for tsunami is accurately calculated and ocean surface heights are detected from readings of tidal sensors and ocean bottom sensors Buoys near anticipated sources detect a tsunami in its early stages and transmit to the PTWC in Hawaii (since seismic waves travel faster than tsunami waves) H2 Volcano Lava are molten rock that erupts onto Earth's surface Magma travels to Earth's surface through an upward tunnel Rock cycle Metamorphic Rocks start to melt at 800 - 1200 Celsius Igneous: hardened magma Sedimentary Intrusive vs Extrinsic: beneath surface or above Magma properties Basaltic Lava: 50% silica Cinder Cones and Shield Volcano Basaltic lava: low viscosity, Downloaded by ?? ? ([email protected])  lOMoARcPSD|27413003 Higher temperature due to low percentage silica Andesite Lava: 60% silica Rhyolite Lava: 75% silica Stratovolcano Most explosive, high viscosity traps air Stratovolcanoes have relatively steep sides because their magma has moderate to high viscosity so lavas flow a short distance before cooling Caldera: collapse of magma chamber Important constituents SiO4 tetrahedron anionic group Water: lowers stiffness, more explosive Eruption categories Eruptions work due to gravity, build up and overflow of lava Hawaiian Properties < a few hundred meters of eruption Mount Kilauea: Hot spot volcano Mount Puʻu ʻŌʻō: Subsidence of lava lakes, due to water getting into high temperature magma, producing high pressure gas bubbles, that cause more explosive eruptions Plinian: Subduction zone volcanos & Stratovolcanoes Plinian Column reaches Mesosphere Gas thrust (Lower 1-2km) - vertical motion Convection region - vertical motion Umbrella region - horizontal motion with the wind Downloaded by ?? ? ([email protected])  lOMoARcPSD|27413003 Large amount of Pumice Powerful gas blasts lighter particles travel further Large amounts of magma erupted Caldera formation possible Rhyolitic magma Mount Vesuvius Mount St. Helens Mount Santorini Pyroclastic Deposit Ash fall Pyroclastic flow Hot gases that glows red Pyroclastic surge: a wave of steam associated with pyroclastic flows Consequences of Volcanos: The hazard posed by a volcano depends on both the population nearby and the eruption product. Hazards without eruption 1. Ground shaking 2. Fractures & Fissures 3. Outgassing: Leakage of dense CO2 into soil or percolate into air near ground level Suffocation of living things High CO2 concentrations in soil interfere with nutrient intake Mammoth Mountain: CO2 makes up to 20-95% of soil content, slowly killing a southern patch of forest 4. Acid lakes Gases from magma dissolve into crater lakes to form acidic water as low as 0.1 pH Downloaded by ?? ? ([email protected])  lOMoARcPSD|27413003 Ijen Crater lake, East Java 5. Lahars & Landslides Lahar: watery volcanic mudslide, grow as they flow and erode anything on the slopes lahars move rapidly down valleys like rivers of concrete lahars and excess sediment cause serious economic and environmental damage to river valleys and flood plains lahars pick up material as they travel, which can cause damage to structures in their path Triggered by eruption or heavy rain soaking fresh volcanic deopsits, quick flows at 10s of m/s Puyallup, Washington: community build on old lahar deposit, unstable Direct hazards with eruptions 1. Lava flows By far the least hazardous one, most lava flow is slow Temperature, silica content, extrusion rate and slope angle Cold & high silica flows do not travel far due to high viscosity Greatest hazard to property though Iceland volcanos are known for beautiful watery lava flows, they form the Icelandic islands 2. Pyroclastic flow: "broken fire" High density mixtures of hot, dry rock fragments and hot gases You can outrun it, the truck could during Pinatubo 1991...but you may want a head start 80km/h, 200-700℃ clog streams, create dams that flood the area (it was very bad for Philippines during Pinatubo 3. Ash fall Small fragments of rock that rain down from the umbrella of a Plinian Column Travel downwind and cover massive area Visibility, dense enough to collapse roofs, damage engines, power generation, transmission and distribution, clogs water supplies, breathing difficulties, crop damage 4. Ground shaking 5. Fissuring 6. Outgassing 7. Landslides & Tsunami Collapse of northern sector of Mt. St Helens 1980 Outwards bulge due to magma flow into edifice, causing a lateral blast that causes an entire northern sector to collapse Hawaiian Islands Some islands such as Alika 1 & 2 are formed from sector collapses with deposits of up to 100-200 km Downloaded by ?? ? ([email protected])  lOMoARcPSD|27413003 1500 to 200km^3 of deposits, forming a tsunami that deposits 325 m above sea level A hypothetical collapse of the southern flank of Kilauea: Trans-Pacific tsunami 6 hours out > 10m wave heights that can hit as far as Antarctic Coast An incipient landslide scar indicates that a sector collapse is imminent Indirect hazards with eruption 1. Air travel Damage to jet engine, cockpit window, air conditioning system, electrical hydraulic and fuel systems AVOID at all costs, regardless of ash concentration Eyjafjallajökull 2010: largest breakdown of European airspace since WWII Commercial Aircraft unable to pass through ash cloud 20-35k ft in the air US$4,7 billion impact in a week Business and leisure travel delayed or cancelled, perishable goods lost, industry production suspended Kelut 2014: SE Asia affected 2. Climate change Ash physically blocks sunlight: H2O, SO2, CO2, HCL, OClO, BrO Pinatubo 1991: 0.5℃ drop in global temperature Optical depth: measure of SO2 concentration increased global stratospheric optical depth 10-100x pre-eruption levels Tambora 1815: 0.4-0.7℃ drop for 3 years, famines, typhus and cholera epidemics Toba 73k BP: up to 15cm ash layer, ash layer at least covered Indian subcontinent, 6–7-year cold snap in ice cores (3-3.5℃ temperature drop) Hotter summers: Tonga 2022 eruption and China Europe heatwave “ 50km column The worst-case scenario: Super volcanos Eruption with ejecta volume > 1000km^3 Volcanic Explosivity Index 8 eruptions; the older the more concern, one cycle might be ending soon... Taupo zone NZ, 26500 years ago Toba Sumatra, 74000 years ago Yellow stone 640000 years ago (2-million-year cycle) Cerro Galan Argentina, 2.5 million years ago Pacana Chile, 4 million years The idea that gases from magma can dissolve into water and form acid lakes is. True, and the acidity can go as low as pH=0.1 (very strong acid, enough to can serious burns to human skin) Volcanic losses to life and property depend on the eruption products and the population density and density of assets located near the volcano Downloaded by ?? ? ([email protected])  lOMoARcPSD|27413003 Historical records of volcanic eruptions are effective in identifying areas at risk for volcanic dangers are difficult to obtain since they depend on written history cannot be used for prediction since volcanoes are inherently unpredictable are difficult to obtain since they depend on written history are easily used to accurately predict the time of an eruption Forecasts of the Mt. St. Helens eruption in 1980 were mostly correct, but were not acted on properly by authorities and residents How did the 2022 Tonga volcanic eruption produce a tsunami? The atmospheric pressure perturbation from the eruption triggered tsunami. The explosion displaced large amounts of seawater. Volcanic material entered the sea and displaced large amounts of seawater. The top of an underwater volcano collapsed down when the magma beneath it erupted, disturbing the seafloor. The last supervolcano eruption at Toba volcano (73,000 years ago) caused what effect on climate? The earth cooled by ~3 degrees C for 6-7 years because ash blocked the sun’s rays and altered the albedo. One reason why it is difficult to mitigate the hazards from volcanoes is that: Volcanic eruptions can behave in unpredictable ways, such as the landslide that caused the Mt. St. Helens eruption to explode sideways Volcanoes sit above the molten mantle, so they potentially have unlimited eruptible magma Each eruption is sourced from a different pool of magma, so we cannot use erupted material to learn about the volcano’s behavior H2 Landslides Landslide: movement of rocks and mud down a slope Rockfall: rocks rolling downhill VERY fast 1-100m/s, but short runout; patchy impact Rotational/translational landslide: large volume of material moving downslope quickly Weak interfaces can transform into debris avalanches when water is squeezed out Rotational: curved slip surface Head moves downward and rotates backwards, Toe moves upward It's like a sinkhole mechanism, just that the hole overflows and flows out Dramatic rotation near the top of landslide, near vertical head scarp Fast (1-10m/s), long distances (shorter than translational) Translational: planar skip surface Either coherent block, or disintegrated debris slide Preserves topography features Long distances and fast Debris flows: wet flow Glacial areas, relatively fast 1-10m/s Long runouts (>50km) Downloaded by ?? ? 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