By Ms.Kopchick

Volcanoes

What are volcanoes?A Volcano is a gap in the earth where molten

rock and other materials come to the earth's surface. Some volcanoes are just cracks in the earth's crusts. Others are weak places in the earth's crust, which occur on places where magma bubbles up through the crust and comes to the earth's surface. Magma is molten rock that occurs by partial melting of the crust and the mantle by high temperatures deep down in the ground. Once magma comes to the earth's surface it is called lava.

Active and non-active volcanoes

Active volcanoes: which are likely to erupt at any moment

Dormant volcanoes:which lie dormant for centuries, but then erupt suddenly and violently

extinct volcanoes : ones no longer likely to erupt.

Types of MagmaBasaltic Magma: Low viscosity (gentle flow),

Low silica content (about 50 % )Basaltic magma forms Shield Volcanoes

Andesitic Magma: Intermediate viscosity ( can be both gentle and violent), Intermediate silica content (about 60 %)

Andesitic magma forms Composite Volcanoes

Rhyolitic Magam: High viscosity (very violent eruptions), High silica content (about 70 %)

Super volcanoes form out of rhyolitic magma along with Cinder Cones

Structure of a Volcano

3 Types of VolcanoesShield Volcano: broad, sloping sides made

of basaltic lava layers (very gentle eruptions)

3 Types of VolcanoesCinder Cones: smallest of volcanoes, but

have very steep sides. Material called cinders are ejected into the air, fall back to earth and pile upward. Very explosive rhyolitic lava.

3 Types of VolcanoesComposite or Strato-Volcano: built up of

alternating lava and ash /rock particles. Andesitic magma can be both explosive and gentle. The more gentle eruptions form the lava layers and the more explosive eruption form the ash/rock layers

Volcanic MaterialAsh: (volcanic): Fragments less than 2

millimeters in diameter of lava or rock blasted into the air by volcanic explosions. The MOST Dangerous eruptive material! Ash can travel for hundred of miles, it can block out the sunlight and change climate, it is poisonous to breath

Volcanic MaterialBombs: Fragments of fluid or partially fluid

lava or rock larger than 64 millimeters in size that are blasted into the air by volcanic explosions.

Volcanic Material Cinders: Cinders are vesicular lava

fragments 1 centimeter or larger in diameter.

Volcanic MaterialPumice: A light-colored, frothy, vesicular

volcanic rock, usually of intermediate and felsic composition, formed by the expansion of gas in erupting lava. Commonly perceived as lumps or fragments of pea size and larger but can also occur abundantly as ash-size particles. Because of its numerous gas bubbles, pumice commonly floats on water

Volcanic MaterialPyroclastic Flow: Pyroclastic flows are

fluidized masses of rock fragments and gases that move rapidly in response to gravity. Pyroclastic flows can be very hot. They can reach 1075 degrees Fahrenheit. They also move extremely fast, over 60 miles per hour.

Famous VolcanoesMt. Paricutin -----Cinder Cone

Famous VolcanoesMt. St. Helens------------Compostite/Strato

volcano

Famous VolcanoesSunset Crater -------Cinder Cone

Famous VolcanoesKrakatoa-------Composite/Strato-Volcano

Famous VolcanoesManau Loa -------Shield Volcano

Famous VolcanoesMt. Kilauea ---------Shield Volcano