Volcanic Processes and Hazards PDF

Volcanic Processes and Hazards Dr. Neil J. Porter Introduction to Natural Hazards ESCI-1000 The course material is the intellectual property of Dr. Neil J. Porter. Distribution or publicat...

Volcanic Processes and Hazards Dr. Neil J. Porter Introduction to Natural Hazards ESCI-1000 The course material is the intellectual property of Dr. Neil J. Porter. Distribution or publication of this material in whole or in part is illegal, under the Canadian Copyright Act, RSC 1985  Volcanic Processes and Hazards Overview 4.0 Introduction to Volcanism 4.1 Properties of Igneous Rocks: 4.2 Types of Volcanoes 4.3 Products of Volcanic Eruptions & Landforms 4.4 Volcanic Hazards 4.5 Linkages 4.6 Why Do People Live Near Volcanoes? 4.7 Volcano Monitoring and Forecasting  Volcanic Processes and Hazards mercury has no volcanic activity 4.0 Introduction to Volcanism Mars has volcanic activities Io Jupiter's moon has volcanic activities Volcanism in our Solar System  Volcanic Processes and Hazards 4.0 Introduction to Volcanism: Volcanic Eruptions 50 to 60 volcanoes erupt each year Most eruptions are in sparsely populated areas Nearly 100,000 people have been killed by eruptions in the past 100 years 500 million people live in the vicinity of volcanoes Japan, Mexico, Philippines, Indonesia Western North America  Volcanic Processes and Hazards 4.0 Introduction to Volcanism: Volcanic Eruptions  Volcanic Processes and Hazards 4.0 Introduction to Volcanism – Distribution of Volcanoes Volcanoes are not randomly distributed, but occur in well-defined zones or belts. 2/3 of all active volcanoes on land are located along the Ring of Fire which surrounds the Pacific Ocean  Volcanic Processes and Hazards 4.0 Introduction to Volcanism – Distribution of Volcanoes Tectonic setting determines the type of volcano. - Mid-Ocean Ridges, Subduction Zones & Hot Spots  Volcanic Processes and Hazards 4.1 Properties of Igneous Rocks: Molten rock material below the Earth's surface is called magma. It becomes lava when it reaches the surface. The viscosity of magma is controlled primarily by silica content. Silica content affects viscosity Silica-rich magma does not flow easily and has a high viscosity Viscosity affects the flow of lava and therefore the shape of the resulting volcano In explosive eruptions, tephra is ejected Small fragments of pyroclastic debris An accumulation of tephra is a pyroclastic deposit  Volcanic Processes and Hazards 4.1 Properties of Igneous Rocks: Rock Classification Extrusive igneous rocks Intrusive igneous  Volcanic Processes and Hazards 4.1 Properties of Igneous Rocks: Silica Content rhyolite High silica content (70-75%) high viscosity Andesite Intermediate silica content (60-65%) intermediate viscosity Basalt Low silica content (50-55%) Low viscosity Komatiite Limited silica, (below 40%) Very low viscosity  Volcanic Processes and Hazards 4.1 Properties of Igneous Rocks: Lava Flows Rhyolitic lava flows Flows have broken and blocky surfaces Lava dome Andesitic lava flows Advances slowly 1 to 5 m/day Typically flows are < 10 km long Breaks into angular blocks distincitve cone shape less silica content  Volcanic Processes and Hazards 4.1 Properties of Igneous Rocks: Lava Flows Basltic Lava flows Average flow rates – 30 km/hr Most flows travel between 10 to 50 km from the source Komatiite lava flows Has not erupted in about 2.5 billion years  Volcanic Processes and Hazards 4.2 Types of Volcanoes The shape and eruptive style of volcanoes are related to the chemistry and viscosity of their magmas.  Volcanic Processes and Hazards 4.2 Types of Volcanoes 1. lava dome a. Charcteristic: Rhyolite lava b. shape: dome shaped c. explosiveness: very explosive d. location: inside old volcanoes, vents( cracks that come to the surface and release lava  Volcanic Processes and Hazards 4.2 Types of Volcanoes 2. Composite volcano a. andesite lava b. cone shaped c. explosive d. location: subduction zone and around the Ring of Fire  Volcanic Processes and Hazards 4.2 Types of Volcanoes 3. Shield volcano a. basaltic lava flow b. Roman Shield shape , gentle shape c. non-explosive d. location: hotspots eg Hawaii and Iceland  Volcanic Processes and Hazards 4.2 Types of Volcanoes 4. Shield volcano a. Komatiite lava flows shape: very low profile thin b.. c.. non-explosive d.. around plate bounderies  Volcanic Processes and Hazards 4.2 Types of Volcanoes 5. Cinder volcano a. pyroclastic material b. steep cone shape c. non-explosive d. location: around vents and cracks and fissures  Volcanic Processes and Hazards 4.3 Products of Volcanic Eruptions & Landforms: Pyroclastic Materials pyroclastic material are magma fragments that are explosively ejected by volcanoes, most are solid. Ash < 2 mm primary projectile Lapilli, 2 - 64 mm Bombs, partially molten, > 64 mm Blocks, solid, > 64 mm  Volcanic Processes and Hazards 4.3 Products of Volcanic Eruptions & Landforms: Volcanic Gases Primarily water vapour , Lesser amounts of carbon dioxide, nitrogen, sulfur dioxide, and hydrogen sulfide Erupted sulfur can have widespread, significant effects on climate.  Volcanic Processes and Hazards 4.3 Products of Volcanic Eruptions & Landforms: Depressions formed by explosion or collapse of volcano top. Harrat Khaybar Volcanic Field  Volcanic Processes and Hazards 4.3 Products of Volcanic Eruptions & Landforms: calderaslava  The summit of a volcano collapses into its magma chamber following voluminous eruptions (violent explosions).  Thousands of meters across, hundreds of meters deep.  Volcanic Processes and Hazards 4.3 Products of Volcanic Eruptions & Landforms: lava tubes Forms when the margins and upper surface of the flow solidify. Can move up to 50 km/hr. In some cases, they drain and become empty tunnels.  Volcanic Processes and Hazards 4.3 Products of Volcanic Eruptions & Landforms: ventsHor  Any opening for lava and debris (may be circular or thin fissures)  Can produce flood basalts  Volcanic Processes and Hazards 4.3 Products of Volcanic Eruptions & Landforms: Hot springs Hot rocks heat groundwater discharged at surface  Volcanic Processes and Hazards 4.3 Products of Volcanic Eruptions & Landforms: Geysers Groundwater boils, erupting steam at surface  Volcanic Processes and Hazards 4.3 Products of Volcanic Eruptions & Landforms: pyroclastic sheet deposits Huge sheet-like eruptions of pyroclastic materials  Volcanic Processes and Hazards 4.3 Products of Volcanic Eruptions & Landforms: lava lakes  Volcanic Processes and Hazards 4.3 Products of Volcanic Eruptions & Landforms: Jokulhlaups Ice Contact Volcanoes Erupt beneath or against glaciers subglacial volcanoes erupt, rapidly melting ice and producing huge floods known as jokulhlaups Ex: Iceland, Mt. Garibaldi  Volcanic Processes and Hazards 4.4 Volcanic Hazards What are the most dangerous manifestations of volcanoes? Primary effects lava flows, ash fall, volcanic bombs, pyroclastic flows, pyroclastic surges, lateral blasts, and poisonous gases Secondary effects lahars, debris avalanches, landslides, groundwater and surface contamination, floods, fires, and tsunamis The size of an eruption can be quantified using a scale called the Volcanic Explosivity Index (VEI)  Volcanic Processes and Hazards 4.4 Volcanic Hazards: lava flows Occur when magma reaches the surface Can move slowly or rapidly depending on viscosity and temperature High viscosity moves more slowly  Volcanic Processes and Hazards 4.4 Volcanic Hazards: Lava Flows Basaltic lava flows are the most common pahoehoe Harden with a smooth ropy texture Travel at speeds of up to a few kilometers per hour Aa Harden with a rough, blocky texture More viscous, travels at rates of a few meters per day  Volcanic Processes and Hazards 4.4 Volcanic Hazards: Diverting lava flows (Iceland) Hydraulic chilling bombing Block channels to cause lava flows to take a less damaging route hydraulic chilling Water used to chill and control lava flows Barriers wall construction Walls are used to redirect lava flows  Volcanic Processes and Hazards 4.4 Volcanic Hazards: pyroclastic flows and surges Flows - avalanches of hot rock, ash, volcanic rock fragments Hot and race down side of volcano at speeds exceeding 400 km/hr (~250 mph) Surges - dense clouds of hot gas and rock debris produced by explosive interaction of water and magma Catastrophic if populated area in path  Volcanic Processes and Hazards 4.4 Volcanic Hazards: Pyroclastic Flows and Surges The eruption of Vesuvius and the resulting destruction of Pompeii (Italy) Pyroclastic flows covered 6 km from the summit  Volcanic Processes and Hazards 4.4 Volcanic Hazards: In 1902, the city of St. Pierre on Martinique in the Caribbean. 2 survivors Obliterated by an incandescent pyroclastic flow - nuee ardentes  Volcanic Processes and Hazards 4.4 Volcanic Hazards: lasteral blast Rock fragments, gas, and ash that are blown horizontally from side of volcano Mt. St. Helens: May 18, 1980, 8:32 am – A M 5.1 earthquake triggers a landslide/debris avalanche of the bulge area  Volcanic Processes and Hazards 4.4 Volcanic Hazards: lateral blast 57 people were killed Flooding destroyed over 100 homes Forests to the north of the mountain were flattened Damage exceeded U.S. $1 billion September 23, 2004, Mt. St. Helens reawakened Magma began moving up toward the crater floor The mountain is monitored with seismographs to continuously record events  Volcanic Processes and Hazards 4.4 Volcanic Hazards: poisionous gases Gas emissions usually accompanies lava and ash, but sometimes acts alone carbon dioxide Odorless, heavy gas that can displace breathable air. sulfur dioxide Odorous gas that causes acid rain and can contaminate rock and soil.  Volcanic Processes and Hazards 4.4 Volcanic Hazards: lahors Debris Flows and Other Mass Movements lahors - large amounts of loose volcanic ash and other pyroclastic material become saturated with water and rapidly move downslope  Volcanic Processes and Hazards 4.5 Linkages between Volcanoes and Other Natural Hazards Earthquakes Commonly precede or accompany volcanic eruptions Landslides Sector collapses can cause tsunamis if they enter water Fire Hot lava may ignite plants and structures Climate Change Volcanic ash from an eruption can temporarily cool climate  Volcanic Processes and Hazards 4.6 Why Do People Live Near Volcanoes? People live near volcanoes for a variety of reasons: 1. place of birth 2. unaware of risks 3. limited economic abilities to move 4. believe explosion is unlikely 5. fertile land for farming 6. on some islands all land is volcanic  Volcanic Processes and Hazards 4.6 Why Do People Live Near Volcanoes? Natural Service Functions: volcanic soil Good for coffee, maize, pineapples, sugar cane, and grapes Geothermal Energy Can create energy for nearby urban areas Mineral Resources Gold, silver, etc. and nonmetallic rocks Used for soap, building stone, aggregate for roads, railroads, etc.  Volcanic Processes and Hazards 4.6 Why Do People Live Near Volcanoes? Natural Service Functions: recreation Health spas and hot springs Hiking, snow sports, and education Kilauea National Park creation of new land Hawaiian Islands  Volcanic Processes and Hazards 4.7 Volcanic Monitoring and Forecasting Is It Possible to Forecast Eruptions? Monitoring involves recording and analyzing both physical and chemical changes at volcanoes. Tiltmeters and geodimeters to detect changes to slope elevation and shape Seismometers to.detect harmonic tremors Gas emmisions, thermal, magnetic and hydrologic monitoring are also measured