Week 1 Lectures 1 & 2 - 12 Aug 2024 PDF

# WEEK 1 - LECTURES 1 & 2 - 12 AUG 2024 ## Topography - Earth: you can see the surface roughness, textures, bc it is more dynamic & more active than Mars, applying certain forces can deform the crust of Earth, textures also show the diff loadings applied on Earth's surface, level of activity is st...

# WEEK 1 - LECTURES 1 & 2 - 12 AUG 2024 ## Topography - Earth: you can see the surface roughness, textures, bc it is more dynamic & more active than Mars, applying certain forces can deform the crust of Earth, textures also show the diff loadings applied on Earth's surface, level of activity is stronger on Earth, crust of Earth is more compliant, more plastic, bc it deforms and is much rougher than on Mars. ## Why there are so many natural hazards on Earth & describe the impact of human to natural disasters - Related to the EXPONENTIAL GROWTH of the global human population; human population increasing like mad, average life expectancy is increasing bc of science and technology (more medications to treat diseases, food production to be more efficient, lesser wars). - Interaction between different spheres (hydrosphere, biosphere, etc.) is creating our natural disasters. - Everyday geological processes. - Events are part of nature. ## Human impact - Relates to the size and location of event. - Lesser people and buildings = lesser damage. - More people and buildings = more damage and catastrophic deaths. - Dramatic hazards occur infrequently and in restricted areas = fewer deaths. - Rare, major events (difficult to predict) = more deaths. - Short-term prediction of major events is difficult due to lack of data. - Trends in leisure activities and safety measures affect fatality rate. - Higher fatality rate in developing countries. - Cost of natural hazards increasing (larger economic loss). ## Compare and contrast the status of catastrophe predictions and the relationships among events ### Predicting catastrophe - Some natural events have predictable cycles but usually too many variables and have overlapping cycles. - Prediction is possible but difficult to predict the impact on a global scale. - Recurrence interval increases linearly on a LOG SCALE and increases exponentially on a LINEAR SCALE. - Magnitude is inversely proportional to frequency (bigger the event, less frequent it takes place). ### Relationship among events - Some events are directly related to others and may overlap to reinforce each other. - Past events influence future events. - **FEEDBACK EFFECT:** Some processes result in more rapid changes. - **Global warming**: melts ice → darker ocean water → absorbs more heat energy → melts more ice. - Overlapping effects: eg. high tide + storm surge @ peak = crazy high actual tide. ## Explain general approaches in mitigating the hazards ### Mitigation - **Land use planning**: - Find out where disasters are likely to occur and restrict development there. - (-): they are often too late as the areas are already populated, might ignite political and legal opposition, restrictions are viewed as infringement of personal and property rights. - **Risky development**. - **Insurance**: Mitigates financial impact of disasters. - **Role of government**: - Research nature and behaviour of natural disasters. - Attempts to forecast to mitigate damage and loss of life. - Different agencies/organisations to take charge of different natural hazards. - Public education. - **Living with nature**: - Cannot change natural laws. - Controlling nature will temporarily hinder natural processes; divert the damaging energy to other locations; energy build up → more severe damage. - Must learn to LIVE WITH NATURE AND NOT CONTROL IT. - Mitigation requires HUMAN BEHAVIOUR CHANGE. ## Describe major natural hazards on planet earth - Earthquakes. - Tsunamis. - Volcanoes. - Landslides. - Sea level rise (SLR). - Extreme weathers (storms, floods). - Climate change. - Meteorite and extreme space weather events. # WEEK 2 - LECTURE 3 - 19 AUG 2024 ## Describe Earth structure and explain plate tectonics theory (plate drift, sea mount production, magnetic anomalous, etc.) - Earth's structure (each layer has a unique chemical composition, physical state and can impact life on Earth's surface): - Crust. - Mantle. - Outer core. - Inner core. - Temperature increases as you move towards the centre (core) of Earth. ## Lithosphere - The solid, outer part of the Earth. - Includes crust + upper mantle. - Bounded by the atmosphere above and asthenosphere below. ## Continental Drift (1912) - Alfred Wegener - Earth's continents have moved over geologic time relative to each other. - Thus, appearing to have "drifted" across the ocean bed. ## Plate tectonics - Is a scientific theory that explains how major landforms are created as a result of Earth's lithosphere movements, which can explain many phenomena, including mountain building events, volcanoes and earthquakes. ## Earth's magnetic field - When a volcanic rock erupts, the particles of magnetic minerals that are contained in the rock want to align with Earth's magnetic field. - But the magnetic particles can only move when the rock is hot. - Once it cools, the particles are frozen in place. - But Earth's magnetic field periodically reverses (N becomes S, S becomes N; aka magnetic reversals); hence we get some rocks with magnetic fields frozen in the current orientation and some in the reversed orientation. ## Ocean Spreading centers - Linear boundary between 2 diverging lithospheric plates on the ocean floor. - 2 plates move apart from each other. - Molten rock wells up from the underlying mantle into the gap between plates. - Solidifies into new oceanic crust. - (Found at the crests of oceanic ridges) - Global seismicity delineate the plate boundary. - Deep seismicity indicate the slab (old, heavier plate) has been subducted into the deeper part of Earth. - Mid-ocean ridges are higher than the nearby seafloor. # WEEK 3 - LECTURE 4 - 26 AUG 2024 ## Describe three major plate boundary types and the associated hazards ### Divergent - Where 2 plates are moving apart. - The space created can also fill with new crustal material sourced from molten magma that forms below. - Divergent boundaries can form within continents but will eventually open up and become ocean basins. - On land, it produces *rift valleys*. Under the sea, it produces *mid-oceanic ridges*. - Driving forces in plate tectonics: Convection of Earth's (solid) mantle raises hot rocks beneath mid-ocean ridges, these rocks spread laterally, cool, and sink back into the interior of the mantle. ### Convergent - Where 2 plates are colliding. - Subduction zones occur when one or both of the tectonic plates are composed of oceanic crust. - The denser plate is subducted underneath the less dense plate. - The plate being forced under is eventually melted and destroyed. - *Benioff zones*: earthquakes follow the subducting slab. - At continental-oceanic convergent boundaries, oceanic plate subducts because it is denser. - At oceanic-oceanic convergent boundaries, the denser oceanic plate subducts. - Continental-continental convergent boundaries, neither subducts under the other, instead, they push upwards and forms mountain ranges. ### Transform - Where plates slide past each other. - Relative motion of the plates is horizontal. - Can occur underwater or on land. - Crust is neither destroyed nor created. - Because of friction, the plates cannot simply glide past each other. - Rather, stress builds up in both plates and when it exceeds the threshold of the rocks, the energy is released, causing earthquakes. - Transform boundaries are on the edges of plates. ## Describe the role plate tectonics plays in the development of Earth's landscapes - Summary of plate tectonic theory: - Lithosphere is broken into tectonic plates (7 or 8 major plates). - Earthquakes, volcanic activity, mountain building, and oceanic trench formation occur along the plate boundaries (or faults). - Tectonic plates are composed of the oceanic lithosphere and the thicker continental lithosphere, each topped by its own kind of crust. Along convergent boundaries, the process of subduction, or one plate moving under another, carries the edge of the lower one down into the mantle (Area of material lost is roughly balanced by the formation of new (oceanic) crust along divergent margins by seafloor spreading). - Plate movement is thought to be driven by a combination of the motion of the seafloor away from spreading ridges due to variations in topography (the ridge is a topographic high) and density changes in the crust (density increases as newly-formed crust cools and moves away from the ridge). At subduction zones, the relatively cold, dense oceanic crust is "pulled" or sinks down into the mantle over the downward convecting limb of a mantle cell. # WEEK 4 - LECTURE 5 - 2 SEP 2024 ## Describe different types of earthquake hazards ### Ground failure: fault rupture, landslides, liquefaction - Earthquakes are one of the natural disasters that caused the most casualties. - 900 million people live on the Gangetic plain, near a megathrust fault. ### Ground shaking - Eg. 1994 Northridge earthquake, California. - Fault ruptures generate earthquakes, which consist of several different kinds of waves: - P waves - 6km/s. - S waves - 3.5km/s. - P waves come first followed by s waves. - Time between p wave and s wave is short means that the earthquake is nearby wherever you are at. - Surface waves (rayleigh waves & love waves) - <3km/s. - Shaking is the greatest near earthquake source. - Shaking lasts a few seconds to several minutes. - Deadliest contribution to lives lost. - Eg. A 60 metre tower in Kathmandu responses differently to different earthquakes: the tower was not destroyed by the 1934 earthquake but was destroyed by the 2015 earthquake; 1999 Kobe earthquake; 2011 Tohuku earthquake. - Earthquakes don't kill people, Buildings kill people. ### Surface faulting - Clear surface offsets. - Eg. California' solution to the problem of fault rupture: Every "active" fault zone is restricted with respect to land use; Sellers are required to notify buyers but not renters of hazard. - Eg. Chelungpu fault rupture in 1999, Taiwan - a typical thrust fault surface deformation. ### Landslides - Ground shaking can dislodge large masses of unstable rocks and soils. - Especially areas that have experienced *liquefaction* and have steep slopes. - Rainfalls facilitate landslides as it can be a lubricant for surfaces to slip. - Could destroy an entire town/city. - Eg. Landslide triggered by 2015 M7.8 Nepal earthquake destroyed the entire village. ### Flooding - Landslides → Flooding. - Eg. Flooding of the Jian river due to a landslide dam led to creation of Tangjiashan Lake after the 2008 Wenchuan earthquake. - Landslide → debris collapse into river/water bodies → flooding. ### Liquefaction - A phenomenon in which the strength and stiffness of a saturated soil/sand is reduced by earthquake shaking or other rapid loading. The pressures generated during large earthquake shaking can cause the *liquefied sand and excess water to force its way to the ground surface*. Hence structures such as bridges or large buildings constructed on pile foundations might lose the support from the adjacent soil and come to rest at a tilt after shaking. - Eg. Niigata, Japan, 1964 after an Earthquake. ### Changes of land level - Uplift and subsidence. - Eg. coral reef was below water before earthquake; after earthquake, uplift and rose to above sea level (Libuat, Sumatra, during the M8.4 Bengkulu earthquake in 2007). - Shoreline was shifted inland. - Submergence is harder to deal with compared to uplift. ### Tsunami - Other lecture. ## Ground shaking and common ways to mitigate the impact - **Need to know**: - Locations of active faults. - How fast the faults are slipping. - When was the previous big earthquake and their recurrence period. - How does shaking decrease away from the fault. ## Earthquake early warning system - Warning system that issues useful info **AFTER THE OCCURRENCE OF AN EARTHQUAKE**. - In an earthquake, a rupturing fault sends out different types of waves. The fast moving p-wave is the first to arrive, but damage is caused by the slower s-waves and later-arriving surface waves. - Sensors detect the p-wave and immediately transmit data to an earthquake alert centre where the location and size of the quake are determined and updated as more data become available. - A message from the alert centre is immediately transmitted to your computer or mobile phone, which calculates the expected intensity and arrival time of shaking at your location. - Rupture of fault → earthquake happens → p wave detected by sensors → sensors transmit the data to earthquake alert centre → alert centre predicts the location and size of earthquake → alert centre transmits the message to your computer/mobile phone to calculate the expected intensity and arrival time of shaking at your location. ## Earthquake prediction system - To predict an earthquake **BEFORE AN EARTHQUAKE OCCURS**. # WEEK 5 - LECTURE 6 (online lecture) - 9 SEP 2024 ## Physics of tsunami ### Initiation of tsunami - Vertical deformation/movement from earthquake generates waves that propagate away from the deep ocean into coastal areas. - Usually, reverse faults are responsible for earthquake induced by tsunami by uplifting/subsiding a large area of sea floor. - Tsunami waves can propagate throughout the entire ocean. - **Wavelength**: distance between 2 peaks/troughs of waves. - **Period**: time passage of one wave. - **Wave height**: height difference between the peak and trough of a wave. ### Normal waves VS tsunami waves - **Normal waves** (wind-driven waves) have SHORT wave lengths - tens of metres. - **Tsunami waves** have LONG wave lengths - up to more than a hundred kilometres. - When ocean floor deforms, it is a very large area beneath the sea floor. - So, when a big earthquake uplifts the ocean floor, hundreds of kilometres are uplifted simultaneously. - Hence the wavelengths of tsunami waves are hundreds of kilometres as well. - Due to the long wave lengths and high wave speeds, more damages are done to coastal areas. ### Tsunami waves - Propagates towards the coast. - As the waves approaches the coast, wavelength ↓, wave height ↑. - As the waves enters shallow water (approaching the coast), tsunami wave speed slows and its height increases, creating destructive, life-threatening waves. ## Causes and characteristics of tsunamis (earthquake, volcanic eruption, landslide, asteroids) ### Undersea rupture of normal, thrust and megathrust faults - **Thrust Faults**: 2004 Indian Ocean & 2011 Tohoku - takes place on the plate interface. - Stuck area ruptures, releasing energy in an earthquake (if a rupture is 100km wide, initial tsunami wavelength is also 100km). - **Waves get steeper and higher as they come into shallower waters, often becoming a chaotic front**. - **Velocity of a tsunami is related to the depth of the sea**: - Deep ocean, faster waves, lower waves. - Shallow areas, slower waves, higher waves. - Uplift/subsidence of seafloor stimulates tsunami waves. ### Normal Faults: 1933 Sanriku - Normal faulting earthquakes takes place in the deeper seas. ### Factors affecting height of tsunami wave - Earthquake magnitude: Usually magnitude > 8 to produce tsunami. - Area of rupture zone: Tsunami waves cannot be generated if area of seafloor deformation is small. - Rate and volume of water displaced: Should be large enough. - Sense of ocean floor motion: Vertical deformation to produce tsunami waves. - Depth of water above rupture: - Has to occur in deep waters. - Shallow waters do not have enough energy to propagate the waves and produce big tsunami waves. ### Undersea landslides: 1958 Lituya Bay, Hawaiian Islands (Alika 2 collapse on the flanks of Mauna Loa volcano) - Earthquake → Landslide → tsunami waves - A large amount of mass slides into the ocean, tsunami waves generated. ### Undersea volcanic eruptions: 1883 Krakatau, 1628 BC Santorini, 2022 Tonga eruption - Volcanic processes can displace large volumes of waters and trigger tsunami waves. - When undersea volcanic eruptions are large, hot volcanic ash moves faster, hence tsunami waves. - Submarine volcanic explosions, gases coming out of the volcanoes, hence tsunami waves. - Landslides leads to collapse of volcanoes, hence tsunami waves. - Maximum size is still unknown as these types of tsunami waves are rare. - 3 possible causes: - Explosion beneath the seawater, explosion displaces a large quantity of seawater. - Underwater portions of the volcano subside quickly during the eruption, greatly disturbing the seafloor. - Large volumes of volcano material enter the sea and displace seawater (another fairly new cause): volcanic eruption → air pressure waves create tsunami waves - Volcanic eruptions can lead to changes in topography/bathymetry. ### Asteroids (no modern cases): 65 million years ago K-T extinction, Eltanin impact - Average frequency of asteroid impacts is low (1km asteroid impact occurs about once every million years). - 1km asteroid falling into 5km deep ocean → could generate 3km deep cavity → cavity walls collapse → generate tsunami with immense run-up on shore. - **Height of fall** has more effect than volume of mass that displaces water. - **Higher height** means faster speed. - **Speed of meteorites** plays the most important role in generating tsunami. ## Tsunami hazard mitigation ### Land use zoning - Limit buildings to elevations above those potentially flooded areas. - Structures designed to better resist wave erosion and scour. - Orientation of streets and buildings designed perpendicular to wave crest (reduces impact of tsunami waves and increases survival rate). - Well-rooted trees can be planted along potentially flooded areas to slow down water waves. - Large ditch or reinforced concrete wall can be built to reduce impact of first wave. - As long as it can survive the big hits (first wave), the chances of survival increases. ### Tsunami warnings - Warning systems are now perfected for far-field (far from the source tsunami). - Seismic waves travel faster than tsunami waves. - Can give warnings of an hour to a day. - Pacific Ocean Tsunami Warning (PTWC) network. - Buoy Warning System: Buoys near anticipated sources of tsunamis detect a tsunami in its early stages and transmit it to the Pacific Tsunami Warning Center in Hawaii. ### Tsunami hazard maps - Tsunami hazard maps help communities with infrastructural adaptation and emergency planning. - Some good infrastructure practices: - Tsunami-resistant buildings. - Warning signs. - Vertical evacuation structures (eg. Tsunami Evacuation Raised Earth Parks). - Elevated restaurants in Hawaii where the lower level is designed to allow waves to pass through. # WEEK 6 - LECTURE 7 - 16 SEP 2024 ## Explain why some volcanic eruptions are explosive and others are not and give historical examples of each ## Describe and give examples of three broad categories of volcanoes ### Volcano types - **Shield volcanoes** (eg. Hawaii - Mauna Kea, Mauna Loa, Kohala, Hualalai, East Maui): - Low aspect ratio because of the fluidity of lavas, commonly non-explosive eruptions. - FAR LARGER than stratovolcanoes (~200km) bc of the viscosity difference of magma that produces them. - Lavas that erupt on Hawaii are basaltic and contain about 50% silica - erupt at about 1200°C and are very fluid and pasty. - (viscosity increases as temperature decreases). - **Stratovolcanoes** (eg. Mt Vesuvius, Italy): - Higher aspect ratio because of lava viscosity. - Both explosive and non-explosive eruptions. - Smaller than shield volcanoes. - Cinder cones - Most lavas that erupt on volcanoes like Mt. St. Helens are closer to rhyolitic and are about 65 to 75% silica - erupt at about 900°C and are pretty stiff. - **Calderas** (ultra-plinian) - eg. Toba Caldera in Sumatra: - Formed by very voluminous & explosive eruptions. - More than a hundred kilometres in scale. - Closest volcano eruption to Singapore ## Describe basic types of rocks from various volcanic process - **Igneous rocks** - Formed from the crystallisation of magma. - **Extrusive**: fine-grained and quickly cooled, eg. felsic: pumice; mafic: obsidian, basalt. - **Intrusive**: coarse-grained and slowly cooled, eg. felsic: granite; mafic: gabbro ## Rock cycle - Classification of igneous rocks: Mineral composition, Grain size, Texture. ## Importance of silica in magma - Magma range from about 50-75% silica. - More silica, STIFFER magma, HIGHER VISCOSITY; eg. 75% silica: Rhyolite - Less silica, MORE FLUID magma, LOWER VISCOSITY; eg: 50% silica: Basalt ## Importance of water in magma - More water, viscosity decreases (behaves more like fluid), more explosive (especially for Rhyolite). - Explosive reaction comes from the build up of gas within bubbles. - At greater depth, higher pressure, bubble rises up to the surface, pressure decreases, bubble expands, BOOM (eruption is caused by the pressure decreasing too fast). - Viscous, stress builds up easily within the bubble, when it gets to the surface of Earth, pressure is higher because magma surrounding the bubble is stiff. ## Describe a Plinian eruption column ### Eruption types - **Shield volcanoes - Hawaiian-type eruptions** - Lava is very fluid and hot. - Bubbles can expand and escape easily. - Relatively gentle, low-energy eruption. - Magma: - Typically basaltic. - Effusive. - Low silica. - Low viscosity. - Very fluid. - Eg. Pu'u O'o eruption - **Plinian-type eruptions** - Lava is sticky and cooler. - Bubbles cannot expand or escape easily. - Explosive. - Starts with glowing pyroclastic flows. - Forms lava domes with steep sides. - Key characteristics: - Ash and smoke columns that can extend to the stratosphere. - Large amounts of pumice. - Powerful gas blasts. - Large amounts of magma erupted. - Caldera formation possible. - Named after Pliny the Younger. - Mt. Vesuvius, Italy. ### Calderas - Ultra-pilian type eruptions - Key characteristics: - Caldera formation. - Large ejecta volumes. - High energy release. - Massive plumes. - Magma is rhyolitic. ## Types of magma (temperature and mineral content of magma affect how easily it flows) - **Basaltic**: - High in iron, magnesium, calcium. - Low in potassium, sodium. - Ranges in temperature from about 1000°C - 1200°C. - **Andesitic**: - Moderates amounts of minerals. - Ranges in temperature from about 800°C - 1000°C. - **Rhyolitic**: - High in potassium, sodium. - Low in iron, magnesium, calcium. - Ranges in temperature from about 650°C - 800°C. ## Describe three types of volcanic deposits ### Volcanic eruptions and products - **Lava flow**. - **Lahar** (mud or debris flow): Mix of mud, water, magma. - **Pyroclastic flow**. - **Lava dome**. - **Landslide** (debris avalanche). - **Eruption column** → **Eruption cloud**: - Ash fall. - Acid rain. ### Pyroclastic deposits - **Pyroclastic fall (or airfall)**: - Fallout from the Pilnian column blankets the ground with a nearly uniform mantle of fine particles. - Coarser grain size compared to surrounding sediments. - eg. Tavurvur volcano, New Britain, Papua New Guinea - **Pyroclastic flow**: - Deposits fills in the gaps in the ground. - Dense slurries of debris racing down the slopes of the volcano deposit, which concentrate in valleys. - eg. Pinatubo Volcano, the Philippines - **Pyroclastic surge**: - Clouds of debris-laden gas jetting out of the volcano and racing over the countryside forms layers of irregularly bedded ash and blocks. - eg. Santorini, Greece # WEEK 7 - LECTURE 8 - 23 SEP 2024 ## Describe various aspects of hazards associated with two end-member modes of volcanoes ## Able to understand the direct and indirect volcanoes hazards and their impact to the environment and human society - Unlike earthquakes, we often can predict volcanic eruptions, and evacuate large population centres. - This requires careful monitoring, and a willingness to accept false alarms. - We cannot prevent volcanic eruptions, and when they happen there will be large financial losses and human impact. - Even when we successfully anticipate an eruption, we cannot always predict the style and severity. ## Living on (or near) a volcano can lead to ### Hazards (WITHOUT ERUPTION) - **Ground shaking**. - **Fractures/Fissures**: Eg. Mammoth mountain, California. - **Outgassing**: - Volcanoes often leak gas. - Gas may stay in the soil or percolate into the air. - CO₂ is denser than air so it sits near the ground level. - Animals (including people) can suffocate due to the concentrations of this odourless gas. - High concentrations of CO₂ in the soil kill plants by denying their roots of O₂ and by interfering with nutrient uptake. - Although the leaves of plants produce oxygen and absorb CO₂ during photosynthesis, their roots need to absorb oxygen directly. High CO₂ concentrations in the soil kill plants by denying their roots oxygen and by interfering with nutrient uptake. - Eg. Mammoth Mountain, California: trees on the south side of the volcano began dying from high concentrations of CO₂ gas in the soil. - **Acid lakes**: Crater lakes can have pH values as low as 0.1 (strong acid); this is the result of gases from magma, like CO2, SO2, HS, HCI, HF dissolving in water. - **Lahars & landslides**: - Lahar: volcanic mudslide - a mixture of water, rock fragments, soil, etc. flowing down a volcanic slope or a river valley on or near a volcano. - Lahars grow as they flow and erode material on the volcanic slope. - Lahars can be triggered by eruption, or by heavy rain; move at tens of metres per second and destroy communities. - Eg. The city of Puyallup, Washington, is built on top of an old lahar deposit. Many communities are at risk. ### Direct hazards (WITH ERUPTION) - Most types of volcanic deposits can pose hazards. - **Lava flows**: - Least hazardous of all processes in volcanic eruptions. - Rate and distance depend on temperature, silica content, extrusion rate and slope of land. - Cold lava flows (flows with high silica content) will not travel far due to high viscosity. - Biggest hazard is to property. - Eg. Hawaii; Mt. Etna, Sicily; Holuhraun eruption Bardarbunda volcanic complex, Iceland. - **Pyroclastic flows**: - Pyro (fire); clastic (broken). - High-density mixtures of hot, dry rock fragments and hot gases moving away from an eruption vent. - Destroys almost everything in their path. - Moves faster than 80km/h, temperatures 200-700°C - Can block streams and create temporary dams, that will later overtop and cause sudden flooding downstream. - Eg. Mount Pinatubo; Mayon Volcano, Philippines. - **Pyroclastic falls (ash fall)**: - Volcanic ash is composed of very small fragments of rock. - Ash can cover wide areas and travel downwind from the erupting volcano. - Effects: reduces visibility, blocks sunlight, damages engines, dense - can collapse roofs, disrupts power generation/transmission/distribution, clogs water supplies, causes breath difficulty, damages crops, etc. - **Ground shaking**. - **Fissuring**. - **Outgassing**. - **Lahars & landslides**. ### Indirect hazards (WITH ERUPTION) - **Air travel effects**: - Eg. KLM Flight 867: flew into a thick cloud of volcanic ash from Mount Redoubt, captain used backup power to restart the engines. - Eg. Eyjafjallajokull eruption: commercial aircraft were unable to reach altitudes of 40,000ft. without passing through the ash cloud. - Damage to jet engine - possible engine failure, Abrasion to cockpit windows, Penetration of air conditioning system, Contamination of electrical, hydraulic and fuel systems. - Cancelled flights - business and leisure travel delayed/cancelled, perishable goods lost, industrial plants suspended production. - **Climate change**: - Volcanic ashes can physically block sunlight - Drop in global temperatures - Led to famines and epidemics of typhus and cholera - Global climate change: hotter summers ## Worst case scenario for volcanoes - Supervolcano - Volcano capable of producing a volcanic eruption with an ejecta volume greater than 1000km³ (240 cu mi) - Taupo volcanic zone, New Zealand - 26,500 and 254,000 years ago - Toba, Sumatra - 74,000 years ago - Yellowstone - 640,000; 2,100,000; 4,500,000; 6,000,000 years ago - Cerro Galan, Argentina - 2,500,000 years ago - Pacana, Chile - 4,000,000 years ago ## Able to describe basic scientific monitoring of volcanoes ### Volcanic Monitoring - **Volcanic tremor** - seismic signals indicating magma movement. - **Ground deformation** (GPS, InSAR, Tiltmeter) - InSAR (Synthetic Aperture Radar interferometry): mapping the surface displacement from space. - **Gas Monitoring** - Gas samples are collected from fumaroles and active vents. - Gas levels may also be monitored by remote sensing techniques. ### Heat and hydrothermal activity: - **Hydrothermal activity**: demonstrates the presence of magma, not necessarily magma movement. - Thermal features: can be monitored by - Night aerial observations. - Thermal (infrared imaging). - Direct temperature measurements. ### Infrasound - Picks up the vibration of air pressure that can propagate away from a volcanic eruption. - Locating the source of something :) ## Eg. Pinatubo prediction - Different government agencies worked to convince local inhabitants of the severity of the threat. - 3 evacuation zones and 5 stages of alerts; daily alerts announced in major and local news sources. - 60,000 people evacuated before the major eruption. ## Eg. Mt. St. Helens prediction - USGS scientists convinced local authorities to close the volcano to the public based on observations of ground deformation and tremors. - A landslide on the north face of the volcano exposed the magma chamber, producing a sideways eruption. - 57 people were killed, including a geologist. # WEEK 8 - LECTURE 9 - 7 OCT 2024 ## What is a landslide - Landslide: the movement of a mass of rock, debris, or earth and/or mud down a slope. - Sliding takes place from a few metres to a few tenths of metres per second. - Rocks can slide or roll downhill *rockfall*. - May occur when large volume of material moves downslope quickly → *rotational/translational landslide*. - May be wet (rain) → *debris flow*. - May occur gradually → *creep* (very slow; a few centimetres per day). - Downslope ground movement is a natural part of landscape evolution (gravity!!!!!!!!!). - Landslides can cause tsunamis, eg. Hawaii. - eg. Near San Salvador, El Salvador, 2001; Palu Bay area landslide, 2018; Shimla, Himachal, India 2017. ## Mount Kinabalu Earthquake, June 2015 - Magnitude 6.2 earthquake. - Earthquake caused rockfall. - Singaporean teachers and students were killed by rockfalls and landslides. ## Rotational slides - Moves downward and outward above curved slip surface, with movement rotational about an axis parallel to slope. - Head moves downward and rotates backward. - Toe moves upward on top of landscape. - Move short distances. ## Translational slides - Moves faster and farther than rotational slides. - Move on planar slip surface such as fault, joint, clay-rich layer. - Move as long as on downward-inclined surface, and driving mass exists. - Underlying material fails so overlying material slides. ### Different behaviours - Remain coherent as block. - Deform and disintegrate to form debris slide. ## How, where and why do landslides occur ### Physical processes ### What causes landslides - **Driving force**: - Gravity pulls down on material. - External forces contribute - eg. earthquakes, eruptions. - **Resisting force**: - Holds material in place. - Strength of material and amount fo friction. ### Factors contributing to slope failure - **Slope steepness** (slope angle, a): - There needs to be a slope (tilting of land) for a landslide to occur. - Steeper slope, greater driving force, greater likelihood of slope failure. - Angle of repose (critical angle): steepest angle at which any loose material is stable; depends on angularity and size of grains and moisture content. - **Material weight**. - **Moisture content**: Moisture content increases, friction decreases. ### Sources of weakness for planar internal surfaces - Layers in sedimentary rock. - Fractures in any kind of rock. - Contacts between rocks of different strength. - Faults, or slip surfaces of old landslides. ### Cohesion adding to frictional resistance - Frictional resistance depends on: slope angle a, load, cohesion. - Cohesion: important force for holding soil grains together due to surface tension of water (or other glue material) between loose grains. - Cohesion is overcome when driving force is large enough. - **Increase in pore fluid pressure** (deeper underground) **reduces friction and facilitates landslide**. ### Impacts - **Table 8-1** ## Rockfall - Very fast → 1m/s - 100m/s. - Short runout bc the speed is very fast. - Patchy impact - eg. taiwan ## Debris flow - Fast 1cm/s - 10m/s. - Long runout (can be > 50km). - Impact through burial, boulders and dynamic forces. - Level of impact related to sediment concentration, debris content, velocity and depth. ## Translational landslide - Fast 1cm/s - 10m/s. - Long runout (can be > 50km). - Complete impact through burial and dynamic forces. - Can transform into debris avalanche. ## Creep - Slow 0.3mm/year - 3.1cm/year. - Short runout. - Damage to brittle structures through ground movement. ## Cascading impacts - **Flood**: - A landslide dam on Sichuan Dadu River, created by an earthquake 10 days earlier, burst and caused a flood that > 1400km downstream and killed 100,000. - Vajont Dam, Italy: during the initial filling, a massive landslide into the lake displaced 50 million m³ of water, a wave of 250m high overtopped the dam and completely destroyed villages and towns downstream. ## Monitoring - A lot of monitoring comes from the mining industry bc landslides occur a