Formation of the Hawaiian Islands. Volcanoes, Magma, and Hot Spots

Formation of the Hawaiian Islands Volcanoes, Magma, and Hot Spots

Topics Hawai i Ring of Fire Hot Spots Decompression Melting The Hawai i Hot Spot

Hot Spots

Hot Spots The Source of Magma for the Hawaiian Islands

Divergent Boundary Most volcanism occurs at plate boundaries Convergent Boundary

Lithospheric Plates

However volcanism commonly occurs in isolated intraplate regions

These individual spots of volcanism occur over hotter than normal regions of Earth s interior. Regions called hot spots

Definition

Definition Hot Spot - region of the mantle that is hotter than the surrounding rock

Over 100 hot spots have been identified

Over 100 hot spots have been identified Hot spots can occur on the sea floor or on the continents

Hot spots are characterized by a voluminous outpouring of lava

Hot spots are characterized by a voluminous outpouring of lava And very high temperatures: 1200-1400 o C

Hot Spot Magma

Hot Spot Magma Hot spot magmas likely are generated deeper in the mantle than magmas associated with plate boundaries

Hot Spot Magma Hot spot magmas likely are generated deeper in the mantle than magmas associated with plate boundaries Chemical composition slightly different

Hot Spot Magma Hot spot magmas likely are generated deeper in the mantle than magmas associated with plate boundaries Chemical composition slightly different Temperatures are higher

Continental Hot Spots

Continental Hot Spots Two examples: Yellowstone Columbia Plateau

Wyoming

Wyoming Castle Geyser Yellowstone National Park

Yellowstone Caldera

Lava Flows in Yellowstone National Park

Trace of the Yellowstone Hot Spot

Columbia Plateau Flood Basalts

Columbia Plateau Lava Flows

Two Ways to Look At the Structure of Earth

Two Ways to Look At the Structure of Earth Density Structure Mechanical Structure

Density Structure of Earth

Density Structure of Earth Earth can be classified into three layers: 1. Crust 2. Mantle 3. Core

Density Structure of Earth

Density Structure of Earth The relative positions of the three layers: 1. Crust --- outside 2. Mantle 3. Core --- inside

Density Structure of Earth

Density Structure of Earth Crust 5-70 km Mantle 2900 km Core 6400 km

Thickness of the crust in kilometers

Question

Question How do geologists know that Earth is divided into three layers?

Density Structure of Earth

Density Structure of Earth This is a structure based on two criteria:

Density Structure of Earth This is a structure based on two criteria: 1. Density

Density Structure of Earth This is a structure based on two criteria: 1. Density 2. Composition

Density Structure of Earth This is a structure based on two criteria: 1. Density 2. Composition Each layer has a different density and a different composition

Density Differences

Density Differences The crust is the least dense layer

Density Differences The crust is the least dense layer The mantle is more dense than the crust

Density Differences The crust is the least dense layer The mantle is more dense than the crust The core is the most dense layer

Compositional Differences

Compositional Differences The crust is mostly Al silicate

Compositional Differences The crust is mostly Al silicate The mantle is mostly Fe, Mg Silicate

Compositional Differences The crust is mostly Al silicate The mantle is mostly Fe, Mg Silicate The core is mostly Fe

Mechanical Structure of Earth

Mechanical Structure of Earth Earth can be classified into four layers: 1. Lithosphere 2. Asthenosphere 3. Mesosphere 4. Core

Mechanical Structure of Earth

Mechanical Structure of Earth The relative positions of the four layers: 1. Lithosphere --- outside 2. Asthenosphere 3. Mesosphere 4. Core --- inside

Mechanical Structure of Earth This is a structure based on two criteria:

Mechanical Structure of Earth This is a structure based on two criteria: 1. Strength

Mechanical Structure of Earth This is a structure based on two criteria: 1. Strength 2. Viscosity

Mechanical Structure of Earth This is a structure based on two criteria: 1. Strength 2. Viscosity Each layer has a different strength and a different viscosity

Definition

Definition Viscosity - a measure of resistance to flow

Definition Viscosity - a measure of resistance to flow Substances like water do not resist flow and have a low viscosity

Definition Viscosity - a measure of resistance to flow Substances like water do not resist flow and have a low viscosity Substances like ice resist flow and have a high viscosity

Lithosphere

Lithosphere All of the crust and the upper mantle

Lithosphere All of the crust and the upper mantle Averages 80 km thick

Lithosphere All of the crust and the upper mantle Averages 80 km thick Relatively strong

Lithosphere All of the crust and the upper mantle Averages 80 km thick Relatively strong Tends to withstand stress to the point of fracture

Lithosphere All of the crust and the upper mantle Averages 80 km thick Relatively strong Tends to withstand stress to the point of fracture Relatively high viscosity

Lithosphere

Asthenosphere

Asthenosphere Underlies the lithosphere

Asthenosphere Underlies the lithosphere 80 km to 300 km

Asthenosphere Underlies the lithosphere 80 km to 300 km Relatively weak

Asthenosphere Underlies the lithosphere 80 km to 300 km Relatively weak Tends to flow when stressed

Asthenosphere Underlies the lithosphere 80 km to 300 km Relatively weak Tends to flow when stressed Relatively low viscosity

Asthenosphere Underlies the lithosphere 80 km to 300 km Relatively weak Tends to flow when stressed Relatively low viscosity Relatively high temperature

Density Structure Mechanical Structure

Mantle plume

Hotter than surrounding rock Mantle plume

Less dense Hotter than surrounding rock Mantle plume

Rises Less dense Hotter than surrounding rock Mantle plume

Mantle plume rises to the base of the lithosphere

Mantle plume rises to the base of the lithosphere Melting occurs in the upper asthenosphere, at the base of the lithosphere

Decompression Melting

Next Decompression Melting

Silicate contains SiO 2 Back