Volcanoes

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

Types of Volcanoes

• There are 3 main types of Volcanoes:

Shield Cinder Cone Composite

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