Volcanoes

__ are windows to see inside the earth

volcanoes

Volcanoes help us understand Earth’s ___ processes

interior

Many people live near volcanoes and die because of volcanic ____

eruptions

6 types of lava?

basaltic lava, pahoehoe, pillow lava, columnar joints, andesitic lava, rhyolitic lava

Characteristics of basaltic lava?

• mafic

• ex: volcanoes of hawaii

• aa

AA (type of basaltic lava)

chunky lava, full of vesicles

What are vesicles?

small cavities or holes in volcanic rocks formed by gas bubbles trapped in lava as it cools

Pahoehoe

ropy lava, less viscous than aa

Pillow Lava

piles of ellipsoidal basalt

• form underwater

• hot lava interacts with cold ocean

• “plastic skin” develops (like inflating balloon)

pillow lava

Columnar Joints

basalt fracturing during cooling

• roughly hexagonal columns

• form when ___, ___, or ___ flows cool

columnar joints; dikes, sills, lava

Andesitic Lava

intermediate

• flows slower than basaltic lavas

• plus volcanoes (pyroclastic eruption)

• example: lascar volcano, chile

andesitic lava

Felsic

Rhyolitic Lava

• most viscous lava

• plug volcanoes

• PRODUCE MOST EXPLOSIVE ERUPTIONS

• ex: mt st helens

andesitic lava

T/F: olcanoes with Si-rich magma not more likely to explosively erupt than volcanoes with non Si-rich magma

false

T/F: magma with lots of gas also makes more explosive eruptions than magma lacking lots of gas

true

Pyroclasts

broken pieces of rock ejected into air

Ash

fine-grained pyroclastic material- easily goes into atmosphere

Pyroclastic Flow

hot ash gas that flows downhill at high speeds

Left A?

central vent

Right A?

side vent

Top B?

conduit

C?

volcano

D?

dike

E?

sill

Bottom B?

magma chamber

Volcano

hill or mountain made of lava and other erupted material

Central Vent

primary eruption site at the center of a symmetrical volcano

Conduit

igneous intrusion that feeds central vent

Side Vent

volcanic eruption site from side of a volcano

Dike

wall-like intrusion that cuts across layers of wall rock

Sill

sheet-like (table-top like intrusion) that is formed by magma injection between parallel layers of bedded wall rock (does not cut across layers but layers can be later tilted)

Magma Chamber

large pool of magma in the lithosphere

Magma __ through crust and __ or pushes aside wall rock

rises; melts

Magma forms in ___ & rises through cracks in the crust to form a magma ___

mantle; chamber

Magma erupts from ___ & ___ vents, forming ___ which accumulates on Earth’s surface, forming a volcano

central; side; lava

Shield Volcano

broad, gently sloping volcano formed by low-viscosity lava that can flow over long distances (non-explosive eruptions)

• generally >10km tall

• circumference: hundreds of kms

• ex: mauna loa, hawaii

What Volcano Structure?

shield volcano

Stratovolcano (composite volcano)

a steep sided, symmetrical volcano built from alternating layers of lava flows, ash, and rock fragments

• common at CONVERGENT plate zones

• ex: mount fuji, japan

What Volcano Structure?

stratovolcano

Cinder Cone (scoria cone)

small, steep-sided volcano built from pyroclastic fragments (like ash, cinders, and volcanic rocks)

• usually forms short, explosive eruptions

• ex: parícutin, mexico

What Volcano Structure?

cinder cone

Caldera

a large, basin shaped depression formed when a volcano collapses after a massive eruption empties the magma chamber

• lots of magma discharged, volcano collapses, leaving an empty magma chamber (or depression)

• top of volcano collapses into empty magma chamber, leaving a large hole

• ex: crater lake, usa

caldera

Fissure Eruption

• tens of kilometers long

• LARGEST volcanic eruptions

• common at DIVERGENT boundaries (like MOR’s or continental rift zones)

Flood Basalt

• forms from fissure eruptions under continents or on ocean floors

• timing of 3 largest flood basalt events in Phanerozoic Eon corresponds to the timing of 3 largest known mass extinctions (massive releases of toxic gases & climate poisoning)

• ex: columbia river flood basalt

Volcanism occurs where?

at subduction zones, rifts, mid ocean ridges (spreading centers) & hot spots (intraplate volcanism)

What type of plate boundary is a subduction zone?

convergent boundary

What type of plate boundary is a rift?

divergent boundary

What type of plate boundary is a MOR?

divergent boundary

• magma comes from partial melting of subducted oceanic crust

• example: aleutian islands, alaska

What type of convergence? (O-O or O-C)

o-o (subduction zone)

What geologic features are found at an ocean-ocean convergent plate boundary?

deep ocean trenches, volcanic island arcs, earthquakes, subduction zones

• magma is a mixture of: fluids from subducted oceanic crust & re-melted felsic continental crust, & melted materials from the mantle above the subducting plate

• lava types include: andesite & rhyolite

• example: west coast of south america (andes)

What type of convergence? (O-O or O-C)

o-c (subduction zone)

What geologic features are found at an ocean-continent convergent plate boundary?

trenches, continental volcanic arcs, mountain building, earthquakes

• magma comes from decompression melting of the mantle

• lava types include: basalt

• example: MOR

What kind of divergence? (O-O or C-C)

o-o (mid ocean ridges)

What geologic features are found at an ocean-ocean divergent plate boundary?

mid-ocean ridges, rift valleys, new oceanic crust, shallow earthquakes, hydrothermal vents

• magma comes from decompression melting of that mantle & may interact with continental crust

• lava types include: basalt, andesite, and rhyolite

• example: east african rift

What kind of divergence? (O-O or C-C)

c-c (rifts)

What geologic features are found at a continent-continent divergent plate boundary?

rift valleys, volcanoes, earthquakes, eventual formation of new ocean basins

What is a mantle plume?

a column of hot, solid rock that rises from deep within the Earth's mantle

Hot Spot

• magma comes from a mantle plume

• mantle plume is stationary, tectonic plates move over stationary plume = creates a chain of volcanoes

• lava types include: basalt (if ocean) & rhyolite or andesite (if land)

• examples: hawaiian islands (ocean) & yellowstone (land)

• __ flows

• ash ___

• ___ gases

lava, falls, volcanic

Lahar

torrential flow of wet volcanic debris

• caldera collapse

• eruption clouds

lahar

Flank Collapse

catastrophic structural failure of volcano that creates massive landslide

Tsunami

large ocean wave caused by underwater volcanic eruptions, landslides, or earthquakes displacing water

Leading cause of death from volcanoes?

pyroclastic eruptions

Active Volcano ex: mount etna, italy

volcano that is currently erupting, has recently erupted, or is likely to erupt again in the near future

Dormant Volcano ex: mount fuji, japan

volcano that is not currently active, but could erupt again in the future

Extinct Volcano ex: edinburgh’s arthurs seat, scotland

volcano that is not expected to erupt again

• historical records, geological records, & oral stories

• determine age of erupted rocks (geochronology)

• search for active geothermal evidence

• shape of volcano (erosion “flattens” volcanoes over time)

how to tell active from dormant & extinct volcanoes:

Predicting Eruptions – long term

monitoring patterns to predict eruptions years or decades in advance

Prediction Eruptions - short term

• monitoring tools to predict eruptions days to weeks, to sometimes hours in advance

  • increased seismic activity

  • changes in heat flow (from hot magma)

  • changes in volcano shape

  • increased gas & steam emissions