volcanism:any activity that includes the movement of magma toward the surface of the Earth volcano: place where magma reaches the surface What are volcanoes?

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Presentation transcript:

volcanism:any activity that includes the movement of magma toward the surface of the Earth volcano: place where magma reaches the surface What are volcanoes?

MID-OCEAN RIDGE: occurs where plates are moving apart lava flows out smoothly and fluidly from cracks

SUBDUCTION ZONE: occurs at subduction boundaries usually explosive and erupted material is mostly lava

HOT SPOTS: areas of volcanic activity in the middle of a lithospheric plates

Hawaiian Islands are an example

 What are the factors that determine the violence of the eruption? Composition of the magma Temperature of the magma Dissolved gases in the magma

magma: liquid, molten rock underground lava: magma that reaches the surface What is magma & lava?

Factors affecting viscosity - Temperature (hotter magmas are less viscous) - Composition (silica content) 1.High silica—high viscosity 2.Low silica—more fluid (e.g., basaltic lava) the measure of a material's resistance to flow.

What are the two types of lava? felsic: much silica, light- colored, slow moving (continental crust)

mafic: low silica, dark-colored, fast moving (oceanic crust)

PahoehoeLava Aa Lava

Pahoehoe

Aa

Aa

Pillow lava from Hawaii

many magmas contain dissolved gases that are given off water vapor, carbon dioxide (CO 2 ), sulfur (S) magmas with more gases have more explosive eruptions How do gases affect magma?

solid fragments ejected from a volcano ash (fine, glassy fragments) lapilli (walnut sized particles) blocks (hardened lava) bombs (ejected as hot lava) What is pyroclastic material?

lapilli

bombs

blocks

Vent: opening from which lava flows Crater: funnel-shaped pit or depression at top of volcano Caldera:craters whose walls have collapsed  What is the anatomy of a volcano?

What are the 3 different types of volcanoes? Shield Cinder Cone Composite

composed of quiet lava flows form gently sloping, dome- shaped mountain basaltic (mafic) magma

largest = Mauna Loa in Hawaii

Made mostly of tephra and other rock particle Formed from explosive eruptions Not very high, narrow base, steep sides Grantic (felsic) magma

built up of alternating layers of rock and lava explosive eruptions at first with tephra, then quiet with lava forms large, cone-shaped mountains made of grantic and basaltic magma

Mount Fuji

Mount St. Helens Before and After the May 18, 1980, Eruption

What are Igneous Rock Structures? Intrusions – underground rock masses Extrusions – surface rock masses

What are the different types of INTRUSIONS? 1. Batholiths –largest igneous intrusions –Form when huge bodies of magma cool underground –Cover 1000 km

Batholith

INTRUSIONS 2. Laccoliths –Domelike masses formed from magma bulging upward

This laccolith in Red and White Mountain, Colorado, is of Tertiary age. Overlying layers of rock have been eroded.

INTRUSIONS 3. Dike –Sheets of igneous rocks that cut across the rock layer

Dike

INTRUSIONS 4. Sill –Sheet of hardened magma that forms between and parallel to layers of rock

Sill

INTRUSIONS 5Stock –Similar to batholiths but less than 100 km

What are EXTRUSIONS? 1. Volcanic neck: –The plug of hardened magma left in the vent from which lava flowed

Volcanic neck:

EXTRUSIONS 2. Caldera

Aniakchak Caldera formed during an enormous explosive eruption that expelled more than 50 km 3 of magma about 3,450 years ago. The caldera is 10 km in diameter and 500-1,000 m deep.