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# Volcanic Eruptions: Hazards and Impacts ## 1. Chemical Composition of Magma (Nature of Hazard) * **Type of magma:** determines if the eruption is explosive or effusive. ### 1. Low Silica Magma * **Less viscous** (thick, sticky consistency) * **Gentle + effusive eruption** * Lava flows far from...

# Volcanic Eruptions: Hazards and Impacts ## 1. Chemical Composition of Magma (Nature of Hazard) * **Type of magma:** determines if the eruption is explosive or effusive. ### 1. Low Silica Magma * **Less viscous** (thick, sticky consistency) * **Gentle + effusive eruption** * Lava flows far from volcano before cooling, damaging infrastructure and property over large areas. * Rarely kills people as they can avoid the lava flow. * **Example:** 2016 Kilauea, Hawaii eruption * 24 injuries * 600 homes destroyed * USD$800 million damage ### 2. High Silica Magma * **More viscous** * **Violent eruption** * Highly destructive pyroclastic flows (causing widespread damage, injuries, and death). * Volcanic bombs may strike people/property causing injuries and death. * **Example:** 2010 Mount Merapi, Indonesia * Pyroclastic flow travelled 3 km down heavily populated mountain sides. * Volcanic bombs spread over 10 km distance. ## 2. Availability of Surface and Groundwater (Vulnerable Conditions) * **Greater availability** of surface and groundwater leads to a higher likelihood of lahars. * **Increased amount** of people and buildings exposed increases disaster risk. * **Sources:** * Rapid melting of snow and ice on volcano summit (before/after eruption). * Groundwater released through cracks and fractures during eruption. * Existing lakes/rivers * Heavy rainfall * **Example:** Many lahars followed the 1991 Mount Pinatubo, Indonesia eruption. * Due to heavy rain (Monsoon season). * More than 100,000 homes destroyed.