Volcanic Hazards PDF

VOLCANIC HAZARDS VARIOUS VOLCANO-RELATED HAZARDS  Formation 1. LAHARS - Are a specific kind of mudflow 1. when small slope collapses gather water on their way down a made up of volcanic debris. volcan...

VOLCANIC HAZARDS VARIOUS VOLCANO-RELATED HAZARDS  Formation 1. LAHARS - Are a specific kind of mudflow 1. when small slope collapses gather water on their way down a made up of volcanic debris. volcano. 2. through rapid melting of snow and ice during an eruption. 3. from heavy rainfall on loose volcanic debris. 4. when a volcano erupts through a crater lake. 5. when a crater lake drains because of overflow or wall collapse DESTRUCTIVE CHARACTERISTICS  Lahars move rapidly down valleys like rivers of concrete.  Lahars can occur with or without a volcanic eruption.  Lahars pick up material as they travel, which can cause damage to structures in their path.  Lahars and excess sediment cause serious economic and environmental damage to river valleys and flood plains.  VARIOUS VOLCANO-RELATED HAZARDS 2. ASH FALL  FORMATION - refer to all explosive eruption - volcanic ash is formed during products, including particles larger explosive volcanic eruptions when than 2 mm. Consists of fragments of dissolved gases in magma expand and pulverized rock, minerals and volcanic escape violently into the atmosphere. glass, created during volcanic eruption. DEVASTATING EFFECTS OF ASH FALL  HAZARD TO AVATION.  DISRUPTION & DAMAGE TO: - BUILDINGS - TRANSPORTATION - WATER & WASTEWATER - POWER SUPPLY - COMMUNICATIONS EQUIPMENT - AGRICULTURE  HEATH IMPACTS TO HUMANS AND ANIMALS VARIOUS VOLCANO-RELATED HAZARDS 3. PYROCLASTIC FLOWS  CONSIST OF TWO PARTS: - high-density mix of hot lava 1. a lower (basal) flow of coarse blocks, pumice, ash and volcanic gas. fragments that moves along the ground. - They move at very high speed down volcanic slopes typically following valleys. 2. turbulent cloud of ash that rise above the basal flow. DIFFERENT FORMS OF PYROCLASTIC FLOWS  Collapse of eruption column – during a highly explosive eruption, the column ejected upwards into the atmosphere cools and can become too cool and dense to maintain upward momentum.  Boiling over from eruptive vent – during an explosive eruptions, material is erupted without forming a high plume and rapidly moves down slope.  Collapse of lava domes or flows – the fronts of lava flows or domes can become so steep that they collapse due to gravitational force. VARIOUS VOLCANO- RELATED HAZARDS 4. VOLCANIC GASES MAGMA – contains dissolved gases, which provide the driving force that causes most volcanic eruptions. As magma rises towards the surface and pressure decreases, gases are released from the liquid portion of the magma (melt) and continue to travel upward and are eventually released into the atmosphere. HARMFUL EFFECTS OF VOLCANIC GASES 1. Carbon Dioxide trapped in low-lying areas can be lethal to people and animals. 2. Sulfur Dioxide is irritating to eyes, skin and respiratory system. 3. Hydrogen sulphide is very toxic in high concentrations. 4. Hydrogen halides (HF, HCl, HBr) are strong, toxic acids. VARIOUS VOLCANO- RELATED HAZARDS 5. LAVA FLOWS - are streams of molten rock that pour or ooze from an erupting vent. Lava is disrupted during either non- explosive activity or explosive lava fountains. Factors that influence the speed at which lava flows:  Type of lava erupted and its viscosity  Steepness of the ground over which it travels  Whether the lava flows as a broad sheet, through a confined channel or down a lava tube  Rate of lava production at the vent Devastating Effects of lava flows  Lava flows may instigate other types of hazards  Everything in the path of an advancing lava flows will be knocked over, surrounded, buried or ignited by the extremely hot temperature of lava  When lava erupts beneath a glacier or flows over snow and ice, melt water from the ice and snow can result in far-reaching lahars  If it enters a body of water or water enters a lava tube, the water may boil violently and cause an explosive shower of molten spatter over a wide area  Methane gas, produced as lava buries vegetation, can migrate in subsurface voids and explode when heated  Thick viscous lava flows, especially those that build a dome, can collapse to form fast-moving pyroclastic flows VARIOUS VOLCANO- RELATED HAZARDS 6. BALLISTIC PROJECTILES - are rocks that an erupting volcano may hurl into the air. These blocks and bombs travel like cannonballs and usually land within 2 km of the vent. These events may occur without warning and in the absence of a larger magnetic eruption. DEVASTATING EFFECTS OF BALLISTIC PROJECTILES Tephra falls and ballistic projectiles endanger life and property by: 1. the force of impact of falling fragments, but this occurs only close to an eruption; 2. loss of agricultural lands if burial is greater than 10 cm depth; 3. producing suspensions of fine-grained in air and water which clogs filters and vents of motors, human lungs, industrial machines, and nuclear power plants; 4. carrying of noxious gases, acids, salts, and close to the vent, heat; and 5. burial by tephra can collapse roofs of buildings, break power and communication lines and damage or kill vegetation