Types of Volcanoes KEY CONCEPT: TECTONIC PLATE MOTIONS CAN RESULT IN VOLCANIC ACTIVITY AT PLATE BOUNDARIES.

Types of Volcanoes KEY CONCEPT: TECTONIC PLATE MOTIONS CAN RESULT IN VOLCANIC ACTIVITY AT PLATE BOUNDARIES.

Volcanoes

How do volcanoes work?

How do volcanoes work? Magma is forced onto Earth s surface. It dries and hardens, this happens many times over thousands of years. Eventually a mountain called a volcano is formed.

Parts of a Volcano Most volcanoes share a specific set of features. The magma that feeds the eruptions pools deep underground in a structure called a magma chamber. At Earth s surface, lava is released through openings called vents. Flowing lava in the interior travels through long, pipelike structures known as lava tubes.

Where do most volcanoes occur? Volcanoes occur at both divergent and convergent boundaries and also at hot spots.

Types of volcanoes

Cinder cone volcano Smallest type of volcano Most common Made from pyroclastic material (material shot out of a volcano) Form a large crater form from explosive eruptions, very steep Wide crater at the top. Usually only erupt once as the force of the explosion destroys the cone. Usually found near shield volcanoes and Composite cones eg Mauna Loa in Hawaii has more than 120

Mauna Loa Cinder Cones around Mauna Loa

Shield Volcanoes Form Shield from volcano: many layers usually of form runny at hot lava. spots, Usually form from hot spots or sometimes as constructive plate boundaries Very wide, not to steep formed from gentle eruptions not much explosive material in magma successive eruptions build up to form gently sloping volcanoes Biggest type of volcanoes Tallest mountain in the world is Mauna Kea (measures from sea floor to top = 6.3 miles non explosive eruptions kilauea

Kilauea

Mauna Kea, Hawaii

Kilauea

Shield Volcano in New Mexico

Composite volcano: Strato Volcano Eruptions alternate between explosive and nonexplosive formed at both constructive and destructive boundaries. Sometimes they have runny lava layers, other times they have pyroclastic materials (ash, dust, rocks) that form layers. Have a wide base and steep sides sides get steeper towards the summit. Have a crater Example - Mount Fuji

Mount Fuji mt fuji

2 Types of eruptions Explosive: volcanoes that build enough pressure to blow its top, sending pyroclastic material into the air.

Explosive eruptions Felsic flow means magma with high feldspar and silica content. Felsic magma traps water and gas bubbles, which leads to lots of pressure. Silica acts like a cork Explosive eruptions are caused by a build up of high pressure. Lava has a high viscosity this means it flows slowly Convergent zones contain lots of water, therefore have explosive eruptions. Associated with subduction

Non explosive eruptions

Non explosive eruption -Build only enough pressure to allow lava to run down its sides. Mafic flow: refers magma (and rocks) rich in magnesium and iron This type of lava is very runny. It has a low viscosity As magma nears the surface there is little pressure, causing gasses escape easily. Magma low in Silica have quiet eruptions Associated with Mid Ocean ridge eruptions

Pyroclastic Material

Four types of lava Aa: lava that is thick and sharp Pahoehoe: lava that forms thin crust and wrinkles Pillow lava: lava that erupts under water, has a round shape Blocky lava: cooler, lava that does not travel far from eruption, jagged when it dries.

Aa lava that is thick and sharp

Pahoehoe: lava that forms thin crust and wrinkles

lava that erupts under water, has a round shape Pillow lava

Blocky pasty lava lava that does not travel far from eruption, jagged when it dries.

Stages in the life cycle of a Volcano 1 Active erupts regularly eg Mt. Etna, Sicily, Mt St Helen s in USA 2 Dormant Has not erupted in a long time but may erupt again eg Cotoaxi in Peru

Extinct has not erupted in recorded history roughly 10,000 years since last eruption Mt. Togiak in Alaska

Volcanoes at Divergent Boundaries At a divergent boundary, the lithosphere becomes thinner as two plates pull away from each other. A set of deep cracks form in an area called a rift zone. Hot mantle rock rises to fill these cracks. As the rock rises, a decrease in pressure causes hot mantle rock to melt and form magma. The magma that reaches Earth s surface is called lava. Basaltic magma rises to Earth s surface through these fissures and erupts non explosively ( it flows out as runny lava)