Volcanoes!!

What is a Volcano?

Volcano - A Volcano is an opening in the Earth’s surface through which molten material or volcanic gases are erupted.

A volcano can either be a classic volcanic cone…..

Mt. St. Helens, pre-1980

Mount Ranier

a crack in the ground, through which lava erupts……

Or a simple volcanic vent.

How Magma Rises To view this animation, click “View” and then “Slide Show” on the top navigation bar.

Where are volcanoes located?

Major Volcanoes Around the World

Volcanic Settings

How and Where Volcanoes Form Volcanic activity takes place primarily at subduction boundaries, 4. Some of the magma reaches Earth’s surface, and volcanoes form on the overriding continental plate. 1. Water in the subducted rock is released into the asthenosphere. Oceanic lithosphere Continental lithosphere Asthenosphere 3. The magma is less dense than its surroundings, so it rises. 2. The water lowers the melting temperatures of materials in the asthenosphere, leading to magma formation.

Ocean- Continental Subduction Pacific Northwest Volcanoes

Ocean- Ocean Subduction

Ocean- Ocean Subduction

Diverging Boundary Volcano

Hot Spot Volcano

How and Where Volcanoes Form Magma and volcanoes also form at hot spots. Kauai Oahu Direction of Plate Movement The Hawaiian Islands formed over a hot spot. Molokai Lanai Maui Hawaii

Major Hotspots of the World

Plate Tectonics and Magma Generation To view this animation, click “View” and then “Slide Show” on the top navigation bar.

Tectonic Settings and Volcanic Activity To view this animation, click “View” and then “Slide Show” on the top navigation bar.

Volcanoes are classified as either Active, Extinct or Dormant

Active

Dormat Mt. Ranier

Vesuvius

Extinct

Magma and Erupted Materials Parameters of volcanism: Viscosity Chemistry of Magma Gases within the magma Water content of magma

Magma and Erupted Materials Viscosity: Viscosity is a measure of how thick (viscous) and sticky a liquid is. VOCABULARY viscosity lava pahoehoe aa pillow lava pyroclastic material pyroclastic flow

Types of Magma

Felsic Magma Characteristics: -light in color -high viscosity: means it is very thick and flows very slowly. -Associated with composite type volcanoes and continential hotspots -Found along continental-ocean subduction boundaries.

Mafic Magma Characteristics: -dark in color -low viscosity: means it is thinner and flows much faster -Associated with shield volcanoes, rift zones, and oceanic hotspots -Found at divergent boundaries and oceanic hotspots

Gases in Magma Water Vapor Carbon-Dioxide Carbon Monoxide Sulfur-Dioxide Hydrogen-Sulfide

Types of Lava

Pahoehoe Lava

Aa Lava Aa Lava

Pillow Lava

Types of Lava Fragments

Ash

Ash Layers

Pyroclastic Rock- Tephra

Pyroclastic Rock- Pumice

Cinder

Bombs

Blocks Blocks

Volcanic Blocks

Pyroclastic Flows

There are three types of volcanic cones: Cinder ______ – explosive eruptions, small but steep slopes, pyroclastics. _______ – non-explosive eruptions, fluid basaltic lava, gentle broad slopes. _________ – alternating between lava and pyroclastics, explosive and non-explosive eruptions, steep and tall. Shield Composite

Volcano Types To view this animation, click “View” and then “Slide Show” on the top navigation bar.

Volcanic Landforms Volcanoes VOCABULARY A volcano’s shape and structure depend on how it erupts and what materials are released. shield volcano cinder cone composite volcano Shield volcanoes are formed by basaltic lava that flows long distances before hardening. lahar caldera Shield Volcano lava plateau

Shield and Composite Volcanoes

Volcanic Landforms Volcanoes Cinder cones are formed when molten lava is thrown into the air from a vent and breaks into drops. These drops harden into cinders that form a steep cone around the vent. Cinder Cone

Volcanic Landforms Volcanoes Composite volcanoes are formed by layers of pyroclastic materials and lava that have erupted in the past. Composite Volcano

Composite volcanoes

Debris Avalanche and Eruption of Mount St. Helens, Washington To view this animation, click “View” and then “Slide Show” on the top navigation bar.

Nuee ardente: pyroclastic flow, of searing superheated gas and incandescent volcanic ash and dust Mount Pelee, on the Carribean island of Martinique, 1902 eruption. All but 2 of the more than 20,000 people in the town of St. Pierre were killed.

Lava Plateau

Volcanic Landforms Volcanoes A caldera is a large crater-shaped basin that forms when the top of a volcano collapses.

Formation of Crater Lake To view this animation, click “View” and then “Slide Show” on the top navigation bar.

EFFUSIVE ERUPTIONS Generally at hots spots, spreading centers Mantle comes directly to surface Hot lava; low viscosity, very mafic, flows easily, gases escape easily Forms shields, flood basalts

EXPLOSIVE ERUPTIONS Found at subduction zones Magma low temp (800 degrees C), high viscosity, does not flow easilty, more felsic mineralogy, gases trapped, hard to predict explosions Forms composite volcanoes, cinder cones, calderas, aerial bombs, nuee ardente gas flows, very destructive