Module 4 Volcanoes & Tsunamis PDF

Module 4: Volcanoes & Volcanism Volcanoes Volcanoes can be quiet Other types are unpredictable, violent, in an instant, creating chaos Different types of eruptions have to do with many factors including steepness of slope (determines how fast it flows) Volcano: A "vent" throug...

Module 4: Volcanoes & Volcanism Volcanoes Volcanoes can be quiet Other types are unpredictable, violent, in an instant, creating chaos Different types of eruptions have to do with many factors including steepness of slope (determines how fast it flows) Volcano: A "vent" through which lava, solid rock debris, volcanic ash and gases erupt from earth's interior (crust/mantle) to its surface. Can be explosive or nonexplosive. Magma: Molten rock below surface, which may include fragments of rocks and gas Igneous rock: rock formed from magma (as a result of cooling) ○ Plutonic rock: rock formed from magma before it reaches the surface ○ Volcanic rock: rock formed from magma after it reaches the surface as lava Lava: Molten rock that reaches Earth's surface Volcanoes and Magma Volcanic Eruption: lava, gas, pyroclastics ○ Pyroclastics: pulverised rock, lava and glass fragment ejected during volcanic eruption Magma Chamber: reservoir of magma that lies underneath every active volcano Three V's of Eruptions: ○ Viscosity of magma ○ Volatiles of the magma ○ Volume of the magma Magma and Volcanic Eruptions Begin with heat at depth ○ Rock that is superheated will rise ○ As hot rock rises, pressure decreases so some of the "rock" melts (producing magma) ○ Volume expansion leads eventually to eruption ○ Zone of weakness at plate boundaries Three factors cause rock to melt: ○ Raising temperature ○ Lowering Pressure ○ Increasing water content Lowering pressure is most common way to melt rock: decompression melting Chemical Composition of Magmas  Of 92 naturally occurring elements: ○ Eight make up more than 98% of Earth's crust: O, Si, Ai, I, Ca, Na, Mg, K, ○ Twelve makeup 99.23% of Earth's crust: (+Ti, H) ○ Oxygen (-2) and silicone (+4) are by far most abundant Typically join up as SiO4 tetrahedron - bonds with positively charge atoms to form minerals Crust dominantly made up of silicates: minerals containing SiO4 Most of the minerals in crust and mantle rock are silicates Quartz, micah, etc Silicon atom surrounded by 4 oxygen atoms → tetrahedron. Building block, to form many structures in geometry Can form layers Crustal Elements in Weight-Percent Oxides Continental Crust → quartz, feldspar, mica (light minerals) Oceanic Crust → olivine, pyroxene, plagioclase (heavy minerals) Magmas, Minerals & Rocks Elements → Minerals → Rocks Different magma composition = different igneous rocks ○ "Oceanic crust" ○ "Andesites" ○ "Continental crust" Magma & Lava Composition: ○ 45% (ultramafic) to 75% (felsic) of magma by weight is silica (SiO) ○ Water vapour and carbon dioxide are usually present Temperature: ○ Lavas vary in temperature between 750 degrees celsius and 1200 degrees celsius ○ Magmas with high H2O contents melt at lower temperatures Viscosity: ○ Lavas vary in their ability to flow ○ Influenced by silica content and temperature Magma and Lava: Viscosity Viscosity: internal resistance to flow ○ Lower viscosity: more fluid behaviour Water, melted ice-cream ○ Higher viscosity: thicker Honey, toothpaste Viscosity is determined by:  ○ More silica tetrahedra: higher viscosity ○ Higher temperature: lower viscosity ○ More mineral crystals: higher viscosity Magma, Lava and Gas Water → carbon dioxide → sulphur dioxide ○ Basaltic magma: lower water content, lower SiO2: peaceful, safe eruptions ○ Rhyolitic magma: higher water content, higher SiO2: violent, dangerous eruptions How a Volcano Erupts Molten magma is stored in "magma chamber" Magma at depth under too much pressure for gas bubbles to form (gases stay dissolved in magma) As magma rises toward surface, pressure decreases and gas bubbles form and expand, propelling the magma upwards Eventually gas bubbles volume ay overwhelm magma, fragmenting it into pieces that explode out as lava flows, ash and tephra Q 1: Rock may melt by: ____all of the above__________ ----------End of Lecture------------------- Oct 09 2024 Tsuanmis Wind-Caused Waves Waves are described by: ○ Crest: highest part of passing wave ○ Trough: Lowest part of passing wave ○ Wavelength: Distance between two waves ○ Wave Height (amplitude): Height from Crest to trough Waves are described by: ○ Frequency → number of waves passing a specific point each second ○ Period → time between passing waves ○ Water depth → average water depths; determines wave behaviour (surf vs swell) Wind creates waves that cause water particles to rotate in place ○ Most waves caused by frictional drag of wind at surface Size of water-particle orbit is the same as wave height at the water surface ○ Orbital diameter decreases with depth due to decreasing effects of wind ○ Storm wave base: 200M below sea level Wind-caused Waves Height of wave depends on: ○ Wind/velocity/strength: The stronger the wind, the bigger the waves ○ Duration of time wind blows: Strong wind that does not blow for a long period will not generate large waves ○ Fetch: Length (distance) wind blows over open water ○ Consistency of wind direction Wave Equation: Large Fetch + Long Duration + strong winds (wind speed) = Large, Long Period Waves  ○ Fetch is important because the interrelationship between wind speed and duration, both functions of fetch, is predictive of wave conditions Waves typically propagate from the centre of a storm These waves combine with pre-existing waves, creating a confused sea Some waves will move in the same direction as the storm, and grow bigger. Others will head off in the opposite direction, lose energy over time and fade away. As waves disperse from the storm, they settle into groups of different sizes and velocities continuously moving away from the source. This is known as a wave train Wind-caused Waves: Rogue Waves Rogue Waves → Storm systems operate all over the oceans, generating waves that interact. ○ Multiple sets of ocean waves interacting in constructive and destructive interference produce sea swells away from storm fronts. Occasionally, waves become briefly synchronised with their energies united to form a spectacularly tall rogue wave. Rare and short-lived, but destructive to boats Wind-caused Waves: Wave Stages Open Sea ○ Irregular waves that commonly form rogue waves ○ Can be devastating to ships ○ Composed of many waves superimposed Swell ○ Deep-water waves (D=L/2) ○ Far from origin (storm center) ○ Larger wavelength and period waves ○ Travel faster than smaller waves ○ Can travel up to several 1000km but lose intensity with distance from storm centre Surf ○ Near-shore waves (D = L/20) ○ Swells shoals and breaks ○ Can be destructive Wind-caused waves: Rogue Waves Draupner Oil Rig, January 1, 1995 ○ First known measurement of a rogue wave; ~320 km off coast of Norway ○ Design: 19.5m - Actual: 25.9m Wind-casued Waves: Surf Wave Break Bottom of rotating orbit interacts with shallow seafloor near coast Friction slows motion, as waves slow their wavelengths decrease and concentrate energy causing taller waves When wave height-to-wavelength ratio reaches 1:7, wave front grows too steep and breaks Tsunami Japanese word: tsu = harbour, nami = waves Tsunami reach greater height when they enter harbour or other narrow space on shore ○ 8m wave on open coastline ○ 30m wave in narrow harbour Japan, 1896 ○ Offshore earthquake → tsunami 20 min later ○ Highest waves (29m) in narrow inlets ○ 27,000 killed, 10,000 homes destroyed 'Tidal wave': inappropriate term (it is not related to tides) Created by different natural disasters happening below or close to water: ○ Earthquakes: Most common cause ○ Explosive (plinian) volcanic eruptions ○ Caldera collapse as aftermath of volcanic activity ○ (underwater) landslides ○ Meteorite impacts Created most often by earthquakes ○ Vertical shift of ocean floor that offset water mass, released energy is transmitted throughout the ocean in tsunami 70,000 people killed by 141 tsunami in 20th century Single tsunami on 26, December,2004 killed at least 245,000 people in 13 countries around indian ocean Tsunami vs Wind-Caused Waves Wind waves ○ Single wave in entire water mass ○ Velocity depends on period of wave 17mph for 5-second wave; 70 mph for 20-sec wave Tsunami  ○ Huge mass of water with tremendous momentum ○ Velocity: v=(g*d)½ g= acceleration due to gravity; d- depth of water For average d = 5,500 m, v = 232 m/sec (834 km/h) Actual observations of tsunami speed peak at 676 to 772 km/h Wave will slow as approaches shore, but still fast ○ Wind-Caused wave onshore: Surf and wave break ○ Tsunami onshore: Large wave rushing inland Tsunami vs. Wind-Caused Waves Wind Waves ○ Height = range from small ripples up to 20 metres (sometimes higher) ○ Speed = 15-120 kmh ○ Wavelength: varying ○ Periods = 5-25sec Tsunamis ○ Height = open ocean less than 0.6 m; -- onshore up to 90m ○ Speed = jetliner speeds 640-800 kmh ○ Wavelength: 100's of kilometres ○ Periods: minutes (10-60) Tsunami → Higher, faster, with longer periods and wavelengths than wind waves ○ Higher risk at causing damage and fatalities onshore Wavelength & Period vs Height Destructive power of tsunami is not due to height, but due to momentum of large mass, with ultra-long wavelength and period ○ 60 min period tsunami rushes inland for 30 min before water pulls back to form next wave Long wavelengths and periods mean waves can bend around islands and ht all shores - no shore is protected, as they are with wind waves. ○ 2004 Indian Ocean tsunami 100 people killed in Sri Lanka on the "protected" shore opposite side of island where tsunami initially hit Computed Tsunami Arrival Time Tsunami travels around islands causing damage/fatalities on all coasts Black numbers on isographs indicate time in hour Red star = epicentre of Earthquake Red Circles = aftershocks within one day  Question 1: Tsunami are typically about _________ high in the ocean, and 6-15 m high on reaching shallow water ○ 0.1 m ○ 1m ○ 5m ○ 20m ○ 30m Earthquake-Caused Tsumami Fault movements of sea floor ○ Must be vertical movement ○ Result in uplifting or down-dropping seabed ○ Earthquakes of at least magnitude of 7.5 ○ Normal or reverse faults inject lots of energy into water column In subduction zone seaward edge of plate is dragged downward as landward edge bulges upward When stuck area ruptures, leading edge of the overriding plate breaks free and springs seaward and upward, causing a tsunami. Subduction Zones & Tsunami Oceanic crust subducted along (reverse) fault creating friction between both planes along fault In subduction zone seaward edge of plate is dragged downward as landward edge bulges upward over geologic time forming mountain range When stuck area ruptures, earthquakes occurs releasing seismic waves into overlying ocean and crust and overriding plate breaks free Tsunami is caused by released energy creating waves in the water column that travel in all directions from the epicentre. Earthquake-Caused Tsunami: Chile 1960 Chile, 22 May 1960: thor wave was the biggest  ○ Magnitude 9.5 subduction event was the most powerful earthquake ever recorded, created large tsunami. ○ Three waves, each successively larger, hit chilean coast, killing 1,000 Chileans ○ Adequate warning was given in Hawaii but 61 people killed anyway- many thought danger had passed after the second wave ○ Tsunami continued to Japan, killing 185 people ○ Could continue to be measured in Pacific Ocean for a week Earthquake-Caused Tsunami: Alaska 1964 Magnitude 9.2 subduction earthquake killed 122 people along sparsly populated Alaskan Coast Alaskan continental plate shifted horizontally up to 19.5 metres and uplifted up to 11.5 metres Tsunami hit Vancouver Island, then California Series of waves, with the fifth one the largest Which wave in series will be the largest is not predictable Earthquake-Caused Tsunami: Indian Ocean 2011 Indian Ocean 26 December 2004 ○ 14 countries were affected, more than 245,000 deaths ○ Fault 1,200 km long ruptured west of Sumatra near Andaman Islands ○ Subducting Indian-Australian plate, when ruptured, raised the seafloor tens of feet In 1883, eruption if Krakatau caused a similar tsunami in the Indian Ocean ○ 36,000 casualties ○ World population was 4x larger in 2004 casing more deaths: >245,000 Quesstion 2: Eq related Tsunami are created by sub-sea fault movements with pronounced vertical offsets of the seafloor. Such movements occur mostly along _________________ A. Oceanic transform faults B. Seafloor spreading centres C. Subduction zones D. Continental rift zones Volcano-Caused tsunami: Krakatau, 1883  Krakatu, Indonesia, 26 to 27 August 1883 Volcanic eruptions & explosions increased in frequency and strength, w/ volcanic masses (Pyroclastic flows) flowing into sea and creating tsunami Culmination of eruption sequence was collapse of mountain int partially emptied magma chamber (caldera), creating tsunami 40 m high ○ More than 36,000 people killed ○ Volcanic eruption killed most people from tsunami and not plinian eruption Volcano-Caused Tsunami: hunga Tonga-hunga Ha'apai, Tonga Jan 15, 2022 @ about 5pm Volcanic ash and gas: up to 58 km VEI = 5; 6.5 to 10km3 Tongan Islands: ○ Waves: up tp 20 m ○ Displaced 1500 people and 4 fatalities Pacific shores: ○ Damage in Peru, Fiji, Hawaii, Chile, California, etc.. → worldwide wave increase Japan: ○ First arrival: 8:20p.m. - 0.3 m (meteotsunami) → 1100 kmh ○ Second arrival: 11:55p.m. - 1.5 M (classic tsunami) → 700 kmh -------End of Lecture------ Oct 25 Lecture Tsunami pt 2 Volcano Associated Landslide: Anak Krakatau Sundra Strait Tsunami: December 22, 2018 Anak Krakatau: breached sea level in about 1928 to more than 330m above sea level in 2018 ○ Abundant volcanic activity starting in June 2018; 423 eruptions on December 22 Collapse of SW side of caldera: 338 metres to 110 metres - occurs at high tide About 456 people killed, no tsunami warning system for volcanoes ○ 2 to 13 m waves Volcano Associated Landslide: Kilauea  Coastal area southeastof Kilauea (active volcano on Big Island of Hawaii) ○ Slides at up to 25 cm/year into the ocean ○ A major movement could create tsunami up to 40 m high ○ Directed to southeast Kilauea sliding into the pacific major slide would cause tsunami up to 40m height "Volcano Associated" Landslide: Hawaii Slump and debris-avalanche deposits cover more than 5 times land area of islands Also, flank-collapses, where entire side of volcano breaks off and falls into the sea Huge tsunami when island collapses into ocean ○ Slump and debris avalanche deposits could cause major tsunami when released into Pacific "Volcano Associated" Landslide: Canary Islands Volcano Collapses: Canary Islands in the Atlantic Ocean ○ Three of Canary Islands have had mega-collapse, last one 15,000 years ago ○ Next mega-collapse could send powerful tsunami to coastlines of Africa, Europe, North and South America ○ Models simulate 10 to 20 high tsunami across Atlantic Ocean striking the coast of North and South America Tsunamis and Landslides Landslide → Mass movement that release huge volumes of rock and soil due to gravity causing masses to move downslope Potential causes: ○ Earthquakes ○ Instability of ground due to heavy rain, snow melt, rising ground water levels ○ Volcanic activity ○ Human activities Rock and soil masses released into water (lake or ocean) causes waves that can create a tsunami Landslide-Caused Tsunami: Earthquake-Triggered Papua New Guinea, 17 July 1998 Magnitude 7.1 earthquake 20km offshore Three successfully larger tsunami hit the shore Third wave was 10 metres high, 4 to 5 km across, travelled at 15 mph, lasted more than a min 2,200 fatalities, four villages on barrier beach decimated Seiches Seiche → oscillating waves in enclosed body of water that slosh back and fourth ○ Occur in sea, bay, lake, swimming pool ○ Swish-French = back-and-forth Energy causing seiche comes from variety of sources: ○ Strong winds ○ Earthquakes Common in Great Lakes of North America Hebgen Lake, Montana, 17 August 1959 ○ Two faults under lake shifted in 6.3M and 7.5M earthquakes ○ Eyewitness accounts of water migrating from one end of lake to other, over 11.5 hours Tsunami Hazards Most hazards occur as direct result of tsunami: ○ Damage of coastlines ○ Destruction of buildings and beaches ○ High fatality rates esp on coast lines Tsunami is a potential secondary hazard of both earthquakes and volcanic eruption Most fatalities and damage occur: ○ On highly populated coastlines ○ Areas with no or low warning system ○ Bad infrastructure/poor concentration ○ Ares altered by human activity: Deforestation Tsunami and You If you feel an EQ and are near water -- possibility of tsunami ○ Mild shaking (>25 secs): powerful, distant EQ generated by tsunami ○ Sea may withdraw significantly, or may rise before first big wave ○ Water changes character, makes unusual sounds Take action: ○ Run to higher ground ○ Inform poeple close by about potential tsunami Tsunami Alert System: Take Action  Tsunami and You Simeuele Island, Indonesia, dec 26, 2004 ○ Closest inhabited land to epicenter of M9.1EQ ○ After shaking stopped, residents fled uphill ○ Only 7 outof 75,000 inhabitants were killed ○ Oral history reminded people: when ground shakes, run to hills before giant waves arrive Nicarauga, 1 sept 1992 ○ Subduction earthquake shifted ground very slowly, creating little ground shaking, but transmitting energy into water very efficiently, generating large tsunami ○ 13,000 homes destroyed and 170 people killed Tsunami and You: Humans can increase the Hazard Coastal areas of India, Indonesia, and Sri Lanka hit hardest by the 2004 tsunami where deforested ○ Trees and shrubs absorb energy In Sri Lanka, areas hit hardest were where coral reefs were removed ○ Destroyed for beaches, with dynamite fishing, and to sell as souvenirs ○ Reefs absorb energy so tsunami do not travel as far inland Tsunami and You: Tsunami Warnings Seismic signals and pressure sensors Sensors automatically detect and analyse seismic waves for tsunami potential National Oceanic and Atmospheric Administration (NOAA) also has pressure sensors throughout the pacific ○ Deep-ocean Assessment Reporting of Tsunami (DART) ○ Pressure sensor transmit to buoys that relay to satellites that trigger warning systems Japanese Tsunami: March 11, 2011  Tohoku earthquake magnitude 9.0, epicenter: 70 km off Japan's northeast shore ○ 5th largest earthquake globally Japan: ○ Most prepared nation in the world for Tsunami with expensive warning system Higher than expected waves: entire towns were obliterated along a 670 km stretch of coastline Cost: most expensive in 2011 Death toll: ~19.500 people. -----End of Lecture Slides----