Objectives:

Describe how volcanoes can affect people.

Describe conditions that cause volcanoes.

Describe the relationship between volcanoes and Earth’s moving plates.

Inside of Old Smokey,All covered with snow,Lurk tons of hot magma,Getting’ ready to blow,From deep in the chamber,Up a vent to the top,Like one great big zit that Is soon going to pop.

The pressure keeps building,And one day – KA-BLOOEY!Out will blast lots of lava,Red-hot and quite gooey.Plus steam and sharp cinders,Dark ash falling down,If I lived near Old Smokey,I’d get out of town. MT. ZITTSAPOPPIN10 MILES

A volcano is an opening in Earth’s surface. Mountains are formed by the lava & volcanic ash after an eruption. Most are dormant which means inactive.

At this time, more than 600 are considered to be active.

The largest in North America –

Mt St. Helens,

Most active in the world -

Kilauea, Hawaii.The eruption of the century is considered to be Mt. Pinatubo, Philippines (1991)

Effects of Eruptions

• Lava is not the only thing about a volcano that is dangerous to humans. When sulfurous gas mixes with water vapor it forms acid rain that can kill vegetation and therefore leaving animals with little to eat.

• Pyroclastic flows is a common and devastating result of some explosive eruptions. The flows are fast-moving currents of hot gas and rock which travel away from the volcano at speeds generally as great as 450 mi/hr. The gas can reach temperatures of about 1,800 degrees.

How do volcanoes form?

Magma forms deep inside Earth because heat & pressure causes rock to melt. Magma is less dense than other rock & is forced upward. After thousands/millions of years it reaches Earth’s surface & flows out through an opening called a vent. The steep walled depression around the vent is called the crater.

Volcanoes form in three kinds of places.

Divergent Boundaries,

Convergent Boundaries,

&

Hot Spots

Divergent boundaries are located where plates are moving apart. They form long deep cracks called rifts. When the magma flows out it is called lava. The lava is cooled quickly by the sea water and sometimes build up to form islands like Iceland. ex. Mid-Atlantic Ridge

Convergent boundaries are where plates move together. As part of one plate is pushed down, it begins to melt and magma is forced up to the surface.

Ex. Pacific Ring Of Fire & Mount Saint Helens.

Hot spots are not located on plate boundaries. They are areas at the mantle’s outer core that is hotter than other areas. Magma is forced upward towards the crust.

Hawaiian Islands

Objectives:

Relate the explosiveness of volcanic eruption to the silica and water vapor content of its lava.

Describe three forms of volcanoes.

All eruptions are not the same. Some are quiet and some are violent. The severity of the eruption affected by

magma composition.

A quiet eruption occurs when a volcano has basaltic magma which contain less silica & is very fluid. This means less pressure. ex. Kilauea

Granitic magma contains a lot of silica. It is very thick & gas gets trapped in vents causing pressure. It also has a high water content which also creates pressure.

Pyroclastic FlowA pyroclastic flow occurs

when an explosive eruption hurls out a mixture of hot gases, ash, cinders, and bombs (large cinders).

Forms of Volcanoes

Shield VolcanoesCinder Volcanoes

Composite Volcanoes

They produce quiet eruptions, and contain basaltic lava. They are broad and it has gently sloping sides.

ex. Hawaiian Islands

They produce explosive eruptions and throws tephra in the air. They typically have steeps sides.

(Material that is thrown into the air by a volcano.)

Composites vary between quiet & violent eruptions.

These have alternating lavers of tephra & lava.

Mount St. Helen's - sequence of eruption

6-3 Igneous Rock Features

Objectives:

•Give examples of intrusive igneous features.

•Explain how a volcanic neck and caldera form.

Sometimes magma forces its way through cracks in the upper crust, but does not reach the surface. The magma cools and hardens into solid rocks. Eventually, the erosion process exposes the rock.

BatholithsIt is largest type of intrusive igneous rock. They form when a large body of magma cools underground. Some have been exposed due to erosion.

YOSEMITE

STATE

PARK

DikeWhen magma squeezed into vertical cracks and hardens.

SillA sill is when magma is squeezed into horizontal cracks.

Palisades over the Hudson River

Volcanic Neck

Sometimes the magma will harden inside the vent and become solid igneous rock. After the cone has eroded away it leaves what we call a neck.

Devils TowerWyoming

Caldera

When the top of volcano collapses into itself.

Crater Lake