Volcanic Eruptions Ms. Pilcher

Vocabulary Mafic lava- dark in color and is rich in magnesium and iron. Felsic lava- lighter in color when cools, high in silica. Pahoehoe- (puh-HOY-hoy) wrinkles that are formed when lava cools rapidly. Aa- (AH-ah) refers to the sharp, blocky texture of volcanic rock.

Vocabulary Pillow lava- round blobs of lava that separate and cool underwater. Pyroclastic material- particles of lava that fly into the air when eruption occurs. Volcanic ash- Particles less than 2mm Volcanic dust- Particles less than.25mm Lapilli- Particles less than 64 mm

Vocabulary Pillow lava- round blobs of lava that separate and cool underwater. Pyroclastic material- particles of lava that fly into the air when eruption occurs. Volcanic ash- Particles less than 2mm Volcanic dust- Particles less than.25mm Lapilli- Particles less than 64 mm

Vocabulary Volcanic bombs- clot of lava that spins through the air and cools. Volcanic block- largest pyroclastic particle that blast from the fissure or vent. Shield Volcano- covers a wide area and generally result from lava eruptions. Cinder Cone- formed from explosive eruption. Composite Volcano- results from altering layers of pyroclastic material and lava.

Vocabulary Stratovalconoes- also known as composite volcanoes, highest volcanic mountains. Crater- funnel shape around the vent of the volcano. Caldera- basin in the crater that is created when slippage occurs.

Vocabulary Stratovalconoes- also known as composite volcanoes, highest volcanic mountains. Crater- funnel shape around the vent of the volcano. Caldera- basin in the crater that is created when slippage occurs.

Volcanic Eruptions The lava that erupts from volcanoes allows us to determine firsthand the material that emerges from the mantle. Scientist has discovered that there are two general types of lava. –Mefic lava –Felsic lava

Mafic Lava Dark in color when hardens. Rich in Magnesium and Iron. Forms much of the ocean crust. When crust cools rapidly, surface will form a crust.

Felsic Lava Lighter in color when hardens Common in continental crust Contains much silica, with lesser amounts of iron and Magnesium

Rock Formations When mafic lava cools and forms wrinkles there called pahoehoe (puh-HOY-hoy) Can break into jagged chunks to form aa (Ah-ah) When lava flows into the ocean and cools rapidly, it often separates and forms pillow lava.

Kinds of Eruptions The kind of lava that reaches the surface determines the force the volcano will erupt. Lava that contains large amounts of trapped gases produces a more explosive eruption of lava.

Oceanic Volcanoes Usually produced by mafic lava. Mafic lava is very hot and thin, and flows like almost as easy as water. Gases escape easier from mafic lava, so erupts are usually quiet. Will flow from the opening like a red hot river.

Continental Volcanoes Most commonly comprised of felsic lava. Tends to be cooler and thicker. Contains large amounts of trapped gases, mostly water vapor and carbon dioxide. When fissure or vent opens, gases escape explosively sending molten particles shooting into the air.

Volcanic Rock Fragments Felsic lava explode throwing pyroclastic material into the air. Formed when lava cools too fast or is sprayed into the air and solidifies. –Volcanic ash –Volcanic dust –Lapilli (luh-PIL-ie) –Volcanic bombs –Volcanic blocks

Volcanic Rock Fragments Volcanic ash –Particles less than 2mm Volcanic dust –Particles less than.25 mm

Volcanic Rock Fragments Lapilli –Particles less than 64mm Volcanic bomb –Round or spindle shape

Volcanic Rock Fragments Volcanic Blocks –Largest pyroclastic material, can be as big as a house!

Volcanic Features Volcanic activity produces a variety of characteristic features on the earth. The lava and pyroclatic material ejected during eruption can build up around the vent. These piles are known as volcanic cones; they are classified into three different types. –Shield Volcano –Cinder Cones –Composite Volcano

Volcanic Features Volcanic activity produces a variety of characteristic features on the earth. The lava and pyroclatic material ejected during eruption can build up around the vent. These piles are known as volcanic cones; they are classified into three different types. –Shield Volcano –Cinder Cones –Composite Volcano

Shield Volcano Covers a wide area Generally results from lava eruption Layers of hot mafic lava flow out around the vent, harden, and slowly build up to form a cone. The Hawaiian Island are a chain of shield volcanoes.

Cinder Cone Made up of solid fragments ejected from the volcano. Most cinder cones have very steep slopes, often close to 40 degrees. Rarely more than a few hundred meters high.

Composite Volcano Many volcanoes have both quiet and explosive eruptions. Composite volcanoes are formed as a result of alternating layers of lava and pyroclastic material. Also known as stratovalcanoes

Craters/ Calderas A creater is a funnel-shaped pit at the top of the volcanic vent. Formed when material is blown out of the volcano by explotion. Calderas are formed when slippage or sinking occurs in the crater.

Predicting Volcanic Eruptions Volcanic eruptions can be one of earth’s most destructive natural phenomena. Scientist are still making progress toward increase there abilities in predicting volcanic activity. Use instruments much like the one they use with earthquake prediction.

Predicting Volcanic Eruptions Things they look for: –Temperature changes within the rock –Fracturing of rocks from pressure build-up –Increase in # earthquake around volcano –Increase is strength of earthquakes –Bulging surface –Change in gases given off by the volcano in the area