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Everything Else About Volcanoes
Including but not limited to how they erupt, the accompanying hazards, the life cycle, features and
predicting eruptions
How a Volcano Erupts
» Magma collects underneath the volcano in a magma chamber
» Pressure from the earth on the chamber forces magma to rise
» Violence dependent on˃ Pressure˃ Dissolved gases
Volcano Video
» http://www.youtube.com/watch?v=u2V2kAGp91I
Hazards
» Lava flows: eruption of magma at Earth’s surface
» Lava flows vary based on the composition of the magma
Pahoehoe
» pahoehoe: fast moving; low viscosity
» smooth ropy texture when it hardens
» move at a rate of about 1 meter per hour
Aa
» aa: slow moving; higher viscosity
» blocky texture when hardens
» move at rates of a few meters per day
Pyroclastic Activity
» Pyroclastic activity: explosive volcanism where tephra is physically blown into the atmosphere
Tephra
» tephra: any material that is blown out of a volcano (mostly ash)
Ash Fall
» ash fall: huge quantities of rock, glass and gas are blown high into the air
» kills vegetation» contaminate water» structural damage» respiratory irritation
Lateral blast
» lateral blast: explosions of gas and ash from the side of the volcano; destroys part of the mountain
Poisonous Gases
» CO2, carbon monoxide, sulfur dioxide, and hydrogen sulfide
» can cause acid rain; contaminates water supply and vegetation
» lahar: debris flows and mudflows» volcanic debris becomes saturated with water» ex. Mt. Pinatubo, Philippines
Volcano Life Cycle
» An active volcano has erupted recently and is expected to erupt again in the future
» A dormant volcano is not active but may become active in the future
» An extinct volcano is at the end of its life and it is no longer able to erupt
Features
» crater - depression found at the top of a volcano; formed by the explosion of the upper portion of the cone
» hot springs: water is heated by the hot rock and reaches Earth’s surface
» geyser: a hot spring that periodically erupts (RARE!)
» ex. Old Faithful
» caldera: a giant crater that can be more than 12.5 miles in diameter
» formed by rare, very violent eruptions» none have occurred in recorded history (they
are 1000 times more violent than Mt. St. Helens!)
» Yellowstone caldera was formed 600,000 years ago!
Predicting Eruptions
» Monitoring of seismic activity- often the earliest sign
» Thermal monitoring - measuring ground temperatures
» Topographic Monitoring - mountain may tilt and swell before an eruption
» Volcanic Gas Emissions - changes in composition of gases may indicates rising of magma
» Geologic History - geologists map and date rocks around the area