volcanoes
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VOLCANOES Chapter 7 Sections 3 & 4
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Chapter 7 Sections 3 & 4. volcanoes. 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. - PowerPoint PPT Presentation
Transcript of volcanoes
VOLCANOESChapter 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 outAsh – fine dust specksCinders – pebble-sized particlesBombs – baseball to car sized
pieces!
ASH CINDERS
BOMBS!
2 types of eruptions1) 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
Volcano Hazards Fire Ash can bury towns Landslides Mudslides Flooding (melted
snow)
Stages of Volcanic ActivityVolcanoes are classifiedas: 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)
