volcanoes - science with smet · types of volcanic eruptions ... •there are 4 main types of...
TRANSCRIPT
What is Inside a Volcano?• A magma chamber filled with molten rock deep
underground that feeds the volcano
• Magma is released through vents during an eruption
Types of Volcanic EruptionsNon-Explosive & Explosive
• Non-explosive eruptions are the most common– Have calm lava flows
– Can release huge amounts of lava
– A lot of the sea floor and NW U.S. are covered with lava
Pu'u O'o volcano in Hawaii
Eruption Video 1Eruption Video 2Eruption Video 3
Explosive
• Explosive eruptions are rare
Clouds of hot ash and gas shoot out
– Molten rock is blown out and cooled into ash
– Ash = tiny pieces of rock, minerals and glass
Types of Volcanic Eruptions
Mt. Saint Helens, Washington State 1980
Best Explosive Eruptions Video
The Types of Magma is Important
Water and Magma = Explosive Eruptions
• Underground, water is dissolved in magma• If magma rises quickly, the decrease in pressure causes
water and other compounds (CO2) to become gases– The gases expand rapidly and explode
• This is similar to shaking a can of soda– The dissolved CO2 is released, the pressure Builds up, and
when the can is opened, soda shoots out
The Types of Magma is ImportantSilica and Magma = Explosive Eruptions
• Silica is a hard colorless compound that occurs as the mineral quartz
– Found mostly in Sandstone
Silica Grains Silica Gel Quartz Sandstone
The Types of Magma is ImportantSilica and Magma = Explosive Eruptions
• Silica-rich magma flows slowly and hardens in a volcano’s vents, plugging it
• As magma builds up behind it, pressure increases until it explodes
• Magma with less silica is more fluid, less likely to plug the vents, and less likely to cause explosive eruptions
What Erupts from a Volcano?• Lava
– Molten rock made up of a slush of crystals, liquids and bubbles
– Mostly Silicon, Oxygen, Aluminum and Iron
• Pyroclastic Flow– Material formed when magma
blasts into the air and hardens
– Move 100 mph and faster
– Can rise thousands of feet
– Reach 800 to 2000 °F
Pyroclastic Flow Video
Lava Video
What’s the Difference Between Magma & lava?
• Magma = molten rock under the Earth
• Lava = molten rock above the Earth
• They are really the same thing, one is just above, the other is below
Viscosity of Lava• Viscosity is how well something flows
– Milk = Low viscosity Milkshake = High viscosity
• The viscosity of Lava affects its surface & appearance
– Viscosity gives rise to different types of Lava
Types of Lava
• There are 4 main types of Lava
Aa Pahoehoe Pillow Lava Blocky Lava“Ah Ah” “Pa ho ho”
Aa• Hawaiian for “stony rough lava” & to “burn”
• Has a High viscosity = flows slowly
• The crust is torn into jagged pieces as lava flows underneath
• Is so named because of the painful experience of walking barefoot across its hot jagged surface
Aa Lava Flow VideoKilauea Volcano, Hawaii
Pahoehoe
• Hawaiian for “smooth, unbroken lava”
• Has a Lower viscosity = flows more quickly
• Has a shiny, smooth, glassy surface
Coke Vs. Pahoehoe Video
Monster Energy Vs. Pahoehoe
Pillow Lava
• Forms from underwater eruptions – Very common
• The lava gets a solid crust when hitting the water,
the crust cracks & oozes out a large blob or “pillow”
Pillow Lava Eruption
Blocky Lava
• Blocky lava = cool, stiff lava that doesn’t travel far
• Oozes from a volcano and forms jumbled heaps of sharp-edged chunks
Blocky Lava Video
Types of Pyroclastic Material
• There are 4 main types of Pyroclastic Material
Volcanic Volcanic Lapilli VolcanicBlocks Bombs Ash
Volcanic Blocks
• Large pieces of solid rock erupted from a volcano
• The 1924 eruption in Kilauea, Hawaii, threw rocks weighing up to 14 tons 3000 feet (10 football fields)
– There were multiple reports of people being hit and crushed by flying rocks
Volcanic Bombs
• Large blobs of magma that harden in the air
– Usually flatten out because they spin in the air
– Can explode from the gas pressure inside as they cool
Volcanic Blocks & Volcanic Bombs Video
Lapilli• Means “little stones” in Latin
• Must be less than 2.5 inches– Anything larger are Volcanic Blocks & Bombs
• Pele’s Tears are a type of Lapilli which looks like tear drops. Lava in the air can form teardrop-shaped glass lapilli. Named after Pele, the Hawaiian goddess of fire.
Volcanic Ash• Forms when gas in magma expands & the walls of
the bubbles explode into tiny glass slivers
– Ash makes up most of a pyroclastic flow
• Very fine ash can stay in the atmosphere for years and travel around the planet by wind currents
Effects of Volcanic Ash - Video
Shield Volcanoes
• Built of layers of lava from many non-explosive eruptions
– Because the lava is runny, the volcano spreads out over a wide area, creating gently sloping sides
• Mauna Loa, in Hawaii is 4,000 feet above sea level
Cinder Cone Volcanoes
• Smallest and most abundant volcanoes
• Are active for only a short time then go dormant
• Made of layers of ash from explosive eruptions
– The pyroclastic material forms steep slopes
Composite Volcanoes• Typically thousands of feet high & steep slopes
• Form from explosive eruptions of pyroclastic flows followed by quieter flows of lava
– This makes alternating layers of ash and lava
Types of Volcanoes Video
Other Volcanic Features
• There are 3 other types of volcanic Landforms:
Craters Calderas Lava Plateaus
Craters• Crater = A funnel-shaped pit at the top of a
volcano
• During eruptions, lava and pyroclastic flows build up material around the central vent
– If lava hardens in the center, the next eruption may blast it away. In this way, a crater becomes larger & deeper
Volcano Crater Video
Calderas• Caldera = Large circular depression of land above a
magma chamber
• Forms when a magma chamber empties and the land above it sinks downwards
• The Yellowstone Caldera is 45 miles wide
Aniakchak Caldera, Alaska
Caldera Formation Video
Lava Plateaus• Most lava comes (not from volcanoes but) from
lava plateaus
• Lava Plateaus are landforms created by repeated eruptions from long cracks in Earth’s crust
• The Columbia River Plateau formed between 14 & 17 million years ago in the North West U.S.– Some places are 2 miles high
Volcanic Lightning!
• Positively charged ejecta (stuff ejected from volcanoes) are separated from the negatively charged ground
• How Lightning Works VideoAwesome Volcano Lightning Pictures Volcanic Lightning Video