Mount Pelee 1902 Mount Pelee St. Pierre 28,000 killed 1 survivor 17 ships in the harbor destroyed Ash cloud swept through town at 125MPH Event lasted 5 minutes Masonry walls 3 feet thick blown apart Temperatures over 10000F

Magma Magma: Molten material consisting of liquid, gas, and a crystals. 1) Basaltic magma: 50% SiO2 , 1-2% gas temperature @ 900-12000C Ca-rich plagioclase feldspar & pyroxene minerals dark - > 40% dark minerals tends to be highly fluid, low viscosity 2) Granitic magma: 65-77% SiO2 , 10-15% gas <8000C temperature quartz, orthoclase feldspar, Na-rich plagioclase minerals light colored - < 15% dark minerals highly viscous - silica tetrahedrons link together to resist flow Magma which reaches the surface and erupts from a volcano is termed extrusive, such as lavas and ash clouds. That which crystallizes underground is called intrusive or plutonic.

Bowen’s Crystallization order of minerals in a basaltic magma Mg, Fe rich: Dark, dense Ionic Substitution 1st to melt Na, K, Al, Si rich Light-colored, less dense minerals

Igneous Rocks Intrusive (slow cooling) Extrusive (fast cooling)

Interlocking Grains Phaneritic texture Quartz Biotite Feldspar

Thin section Biotite Feldspar Quartz

Aphanitic Texture Phenocryst

Glass An amorphous solid--no internal crystalline structure

Magma Generation Partial melting of down-going slab: Si, Al, Na, Ca, K

Crystallization Early-forming minerals, such as olivine & pyroxene and sulfide minerals

Plutonic Rock Features

Intrusive

Intrusive Igneous Rocks

Devils Tower

Sill

Dike, Neck

Batholith

Sierra Nevada

West Coast Batholiths

Basaltic Volcanism Generally non-explosive Basaltic magma: Only 50% SiO2, very fluid Generally results in lava flows, little ash

Mid-Oceanic Ridge 80% of world’s volcanism

Flood Basalts Over 1km thick

Basaltic Lava Flow

Columbia River Basalts

Hawaii

Shield Volcano Builds up over time, lava flow on top of lava flow

Pahoehoe Lava Very fluid, thin, and ropy Outer crust cools quickly, hardens Very fluid, thin, and ropy

Aa Lava Thick and chunky Slow moving

Lava Tube Window

Kilauea, Hawaii Caldera

Ocean

Kalapana, Hawaii

Fountain Fountain

Scoria Vesicular Fe & Mg rich Ejected as liquid

Cone

Cinder Cone

Mauna Kea