Chapter 10- Volcanoes Lecture notes

Broad, gently sloping sidesBroad, gently sloping sides Basaltic lavaBasaltic lava Small amounts of gases and silicaSmall amounts of gases and silica Shield Volcanoes

Material ejected high into the air falls back to EarthMaterial ejected high into the air falls back to Earth Steep sidesSteep sides More water and silica than shieldMore water and silica than shield Large volume of gasesLarge volume of gases More explosive than shieldMore explosive than shield Cinder Cone Volcano

Volcanic fragments alternate with lavaVolcanic fragments alternate with lava Large amounts of silica, water, and gasesLarge amounts of silica, water, and gases Dangerous to humans and environmentDangerous to humans and environment Violently explosiveViolently explosive Composite Volcano

Vesuvius – Sorrento (Italy)

Intrusive igneous rock bodies –Batholiths –Batholiths- largest plutons, irregularly shaped masses, course grained –Stocks –Stocks- smaller than batholiths –Laccoliths –Laccoliths- mushroom shaped –Sill –Sill- forms parallel to layers of rock –Dike –Dike- cuts across layers of rocksPlutons

3 Factors Effect Magma Formation3 Factors Effect Magma Formation –Temperature 800 – 1200c° for rock to melt and form magma800 – 1200c° for rock to melt and form magma Temperature increases with depthTemperature increases with depth –Pressure Pressure increases with depthPressure increases with depth Increased pressure raises a rock’s melting pointIncreased pressure raises a rock’s melting point Raised melting point prevents all rock from meltingRaised melting point prevents all rock from melting Magma Formation

-Water –Water molecules occupy pore space within rocks –Water lowers the melting point of a rock –The more water, the lower the melting point Magma Formation

BasalticBasaltic – rocks in upper mantle melt – low silica – low viscosity – quiet eruptions – very hot ( °C) – fast moving lava – melted basalt Magma Types

AndesiticAndesitic –oceanic crust or oceanic sediment –60% silica (high) –intermediate viscosity –intermediate eruptions –melted andesite Magma Types

RhyoliticRhyolitic –molten material rises and mixes with overlying silica and water rich continental crust –high viscosity –very explosive eruptions –highest silica content –thick, slow movinglava –thick, slow moving lava –melted granite Magma Types

Volcanoes

80% of volcanoes found along convergent boundaries80% of volcanoes found along convergent boundaries –Circum-Pacific Belt- along western coastlines of N. and S. Am. Divergent plates move apart, magma forced upwardDivergent plates move apart, magma forced upward –Ocean ridges (mid-Atlantic) –Iceland

Hot Spot Volcanoes Located away from plate boundary Magma plume rises from core Magma plume rises from core Plume melts the crust Plume melts the crust Islands are formed by escaping magmaIslands are formed by escaping magma Usually forms arcs as a result of moving platesUsually forms arcs as a result of moving plates

Volcanoes and earthquakes are generally located togetherVolcanoes and earthquakes are generally located together Both take place at convergent boundariesBoth take place at convergent boundaries