VOLCANOES

Anatomy of a Volcano

Volcano “Life-cycle” 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

Mount Baker - dormant Mt. Rainier - active Shiprock Peak- Extinct

LAVA vs MAGMA what’s the difference? magma: molten rock inside the Earth lava: magma that has emerged on the Earth’s surface magma lava

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. Which of the volcanic eruptions (2 slides ago) likely had high viscosity lavas?

Which volcanoes below have high viscosity magma/lava Which volcanoes below have high viscosity magma/lava? (CIRCLE YOUR CHOICES)

What causes molten rock to be viscous or not? TWO THINGS Silica The higher the silica content, the higher the viscosity. Temperature The hotter the magma, the less viscous it is.

1. Shield 2. Composite 3. Cinder cones TYPES OF VOLCANOES 1. Shield 2. Composite 3. Cinder cones

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 & sometimes lava tubes: caves left behind after 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

Example: 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

Where are volcanoes?

Plate Boundaries! Ring of Fire Where are volcanoes? Plate Boundaries! Ring of Fire Area of the world where volcanoes are common Outlines the Pacific Ocean

hot spot: area of volcanic activity independent of lithospheric plates (meaning…they don’t move) ex. Hawaii

In MOTION!

Other volcanic features! 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!

Volcanic Hazards Primary Effects Secondary Effects Lava flows Pyroclastic activity Ash fall Poisonous gas Lateral Blast Secondary Effects Lahar

Lava flows: eruption of magma at Earth’s surface Lava flows vary based on the composition of the magma.

tephra: any material that is blown out of a volcano (mostly ash) 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 mountain ex. Mt. St. Helens

- CO2, carbon monoxide, sulfur dioxide, and hydrogen sulfide Poisonous Gases - CO2, carbon monoxide, sulfur dioxide, and hydrogen sulfide - can cause acid rain; contaminates water supply and vegetation FURTHEST WE GOT IN 3RD BLOCK.

Secondary Effects lahar: debris flows and mudflows volcanic debris becomes saturated with water ex. Mt. Pinatubo, Philippines

Predicting Volcanoes (5 factors used) 1. Monitoring of Seismic Activity- often the earliest sign 2. 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 indicate rising of magma

5. Geologic History - geologists map and date rocks around the area