Transcript Geology Notes Part 9 What is a volcano?

Geology Notes
Part 9
What is a volcano?
• A vent or fissure in
the Earth’s surface
through which
magma and gases
are expelled
What is the difference
between lava and magma?
• lava is the molten rock or
magma that has reached
the surface
Lava
Magma
Where do volcanoes
generally occur?
• They generally occur along plate boundaries
when plates collide or move apart
What are the two different
types of volcanic eruption?
• nonexplosive or
quiet eruptions
produce calm flows
of lava
• explosive eruptions
are rare and
rapidly erupt ash
and rock into the
atmosphere
What are the
different
types of lava?
• Aa lava is thin and
forms brittle
jagged crust as it
cools
• Pahoehoe lava flows
slowly forms a
glassy wrinkled
crust
What are the different types of lava?
Pahoehoe
Pahoehoe
Aa
Aa
Aa
Pyroclastic
Materials
What is a shield volcano and
how do they form?
• formed by quiet
eruptions
• thin lava that
spreads out over a
wide area
• sides are not steep
Photograph of the Hawaiian volcano, Mauna Kea, with a light
dusting of snow, seen from Kohala above Kamuela.
Photograph by Eric Guinther provided to Wikipedia under
GNU.
Belknap Shield Volcano, Oregon.
What is a cinder cone volcano
and how do they form?
• Formed by
moderatly explosive
eruptions
• the pyroclastic
material forms
steep sides
Tavurvur, Rabaul Caldera, Papua New Guinea. A small
explosion from Tavurvur sends an eruption column into the
sky a few weeks after it began erupting on September 19,
1994. Lava erupted from the cone in October 1996 and
flowed through the breach in the crater (left center).
Mount Veniaminof, Alaska. Steam rises from the cinder
cone within the caldera of Mount Veniaminof in the final
stages of an eruption in 1983-1984. Lava flows that spilled
down the side of the cone (dark areas) melted a pit in the
summit ice cap about 2.3 x 1 km in dimension.
What is a composite volcano
and how do they form?
• Form from explosive
eruptions followed
by slower flow of
lava
• forms alternating
layers of
pyroclastic material
and lava
• Also known as a
stratovolcano
Mount St Helens
1980
Snow-covered Kanaga Volcano in Alaska erupts a small
column of tephra, gas, and steam. Kanaga is a
stratovolcano.
What is a hot spot?
• A volcanically active area far from a
plate boundary
How can hot spots be used to
determine the motion of
tectonic plate?
• Using the distance of volcanoes (such as the
Hawaiian Islands) and their age, the direction
and rate of plate movement can be
determined. Distance ÷ Time
Current Eruption
Thursday, January 13, 2011 - Mount Etna, Italy
How can volcanoes change the
atmosphere, hydrosphere, and
other Earth systems.
•The lava, gas, and ash that erupt into
the atmosphere can remain in the
atmosphere and be dispersed around
the world by global wind currents.
•The sulfur dioxide combines with
water vapor to form sulfuric acid,
which reflects the sun’s energy back
into space. This can cause global
temperatures to decrease.
•Also the acid rain has a negative
impact on vegatation around the world
How can volcanoes be used to
determine plate boundaries?
•Composite volcanoes usually
form in straight lines along
convergent plate boundaries as
one plate is being subducted
under another.
Convergent Boundaries