VOLCANOES

Chapter 7

Sections 3 & 4

Volcanic Eruptions As magma heats up it

becomes LESS dense and flows upwards.

If there is an opening in the crust, it will reach the earth’s surface – a volcano is born!

Inside a volcano

ERUPTIONS As magma rises the pressure surrounding

it decreases. (It is not as deep anymore) This allows gases in and around the magma to expand. These expanding gases push the magma out of the volcano.

Eruptions can spew out

Ash – fine dust specks

Cinders – pebble-sized particles

Bombs – baseball to car sized

pieces!

ASH CINDERS

BOMBS!

2 types of eruptions

1) QUIET: magma low in silica; magma flows easily, gases bubble out slowly and gently.

2) EXPLOSIVE: magma high in silica; thick/sticky; doesn’t always flow out of the crater; can plug it like a cork; gases get trapped and build up pressure until they “explode”.

PYROCLASTIC FLOW: when the volcano hurls out a mixture of hot gases, ash, cinders, and bombs.

QUIET EXPLOSIVE

SCARY PYROCLASTIC FLOW!

Mt. PinatuboPhilippines

1991 eruption

More pyroclastic flows

Edge of a pyroclastic flow

Pyroclastic flows cause tremendous damage!

Volcano Hazards Fire Ash can bury towns Landslides Mudslides Flooding (melted

snow)

Stages of Volcanic ActivityVolcanoes are classified

as:

1) ACTIVE – a live volcano that is erupting or will in the near future

2) DORMANT – “sleeping” may erupt again

3) EXTINCT – a dead volcano; unlikely to ever erupt again.

TYPES OF VOLCANOES

Wide, gently sloping,

usually form at a hot spot,

lava pours out gently

Lava has high

viscosity, steep, cone shaped hill,

more explosive eruptions

Combination of both; sometimes

gently flowing lava, sometimes

explosive, alternating layers of ash/cinders &

lava

Click for the video clip!

Other volcanic landforms

Lava plateau – lava flows out of several long cracks in an area and eventually over hundreds of years build up to form a plateau

Calderas Caldera – huge hole left by the

collapse of volcano

Soils from Lava & AshWhen hardened lava erodes and forms soil,

phosphorous, potassium and other important minerals are released. These make the soil very fertile.

Dikes and SillsWhen magma forces itself across rock

layers it hardens into a DIKE.

When magma squeezes between horizontal layers of rock it forms a SILL.

Dikes & Sills in New Zealand

Volcanic NecksForms when magma hardens in the

volcano’s pipe and the softer rock surrounding it erodes away.

Batholiths & Dome Mountains

Batholith: large rock masses form the core of many mtn ranges; formed when a large body of magma cools inside the crust.

Dome Mountain: smaller bodies of hardened magma

Batholiths

Sierra Batholith (Yosemite Nat’l Park)

Dome Mountains

Geothermal Activity Geo – means “earth” Therme – means “heat” Geothermal is heat produced

by the Earth (actually magma!) Hot springs & Geysers are

types of geothermal activity found in volcanic areas.

Hot Springs

In IDAHO

In ARKANSAS

GEYSERS (New Zealand)