VOLCANOES
Dec 26, 2015
Volcano Basics• Active – a volcano that has erupted
recently (geologically speaking)
• Dormant – (sleeping) has erupted within the past few thousand years – will likely erupt again
• Extinct – hasn’t erupted in 10’s of thousands of years; unlikely to erupt again
viscosity: a fluid’s resistance to flow
high viscosity = high resistance to flow (THICK)
Low viscosity = low resistance to flow (THIN)
Nope…not movin’
•Low viscosity magmas allow gases to escape easily and move easily through cracks.
• In higher viscosity lavas, gas pressures build up and erupt explosively.
•VIRTUAL LAB!!
The higher the silica content, the higher the
viscosity.
The hotter the magma, the less viscous it is.
Shield Volcanoes
- largest volcanoes (tallest when measured from the ocean floor)- shaped like a gentle arch or shield-basaltic lavas (low silica content)
- usually non-explosive eruptions
- results in lava flows
- found in Hawaii (Mt. Kilauea) and Iceland
Composite Volcanoes- coned shaped; sometimes called stratovolcanoes- lava contains mostly andesite or rhyolite (higher silica content)- more viscous
Combination of explosive activity (pyroclastic) and lava flows
Responsible for most deaths of any type of volcano ex. Mount Saint Helens Mt. Pinatubo Mt. Fuji Mt. Vesuvius
Cinder Cones
- smaller volcanoes- form quickly -are active for a few years and then usually go dormant
ex. Paracutin, Mexico
- 1943, hole in ground- 2 weeks prior, small tremors- 1st day grew 10 m- By 5th day it was 100 m tall- After 2 yrs, it was 400 m tall- went quiet after 9 years
Features of Volcanoes
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: heating and circulation of water forms a pattern (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!
Lava flows: eruption of magma at Earth’s
surface
Lava flows vary based on the composition of the magma.
Pyroclastic Activity: explosive volcanism where tephra is physically blown into the atmosphere
tephra: any material that is blown out of a volcano (mostly ash)
ash fall: huge quantities of rock, glass and gas are blown high into the air
- kills vegetation- contaminate water- structural damage- jet engine “flame out” - respiratory irritation
lateral blast: explosions of gas and ash from the side of the volcano; destroys part of the mountainex. Mt. St. Helens
Poisonous Gases
- CO2, carbon monoxide, sulfur dioxide, and hydrogen sulfide- can cause acid rain; contaminates water supply and vegetation
Secondary Effects
lahar: debris flows and mudflows
-volcanic debris becomes saturated with water-ex. Mt. Pinatubo, Philippines
Predicting Volcanoes
1. Monitoring of Seismic Activity- often the earliest sign2. Thermal monitoring - measuring ground temperatures
3. Topographic Monitoring - mountain may tilt and swell before an eruption
4. Volcanic Gas Emissions - changes in composition of gases may indicates rising of magma