Download Volcanoes

Volcanoes
Volcanoes
Mountains built up by molten rock that
has risen to the earth’s surface through a
vent.
 Volcanologist

– a volcano geologist
Volcano Terms

Molten rock inside the earth
– Magma

The source of magma at the bottom of the
vent
– Magma chamber

Connects the magma chamber with the
earth’s surface
– Vent

Magma that reaches the earth’s surface
– Lava

Layered structure of lava, ash, or both that was
built up by successive eruptions
– Volcanic cone

Secondary cone that forms on the side of the
main cone or is completely separate from it
– Parasitic cone

Depression at the top of the cone
– Crater

Enlarged depression caused by an explosion or
the collapse of a volcanic cone; often filled with
water
– Caldera
Volcanic Emissions
Gaseous Emissions

Dissolved gases separate from the magma
because of reduce pressure as the magma
approaches the surface

Glowing avalanche – mixture of hot
solid particles suspended in water vapor
and other gases
– At night it glows a dull red
– So heavy that it flows quickly down a
volcano’s slope instead of rising into the air
– Also called a pyroclastic flow
– Can move at up to 93 mph and contain gases
from 100-800*C
– Suffocates or incinerates everything in its path

Superheated water vapor
– Lahar – a mud-flow of volcanic ash mixed
with water
At Nevado del Ruiz in Colombia over 23,000 people died
when a lahar, started by a relatively minor eruption of
the volcano, swept down the river valleys on the side of
the edifice and destroyed Armero and Chinchina. The
footage of rescue efforts after the lahar were devastating
and heartbreaking. Sadly, this disaster was mostly
preventable as the citizens of these towns could have
had at least an hour's warning to walk to higher ground,
but the Colombian government did not have an effective
plan in place.
I clearly remember driving through the area hit by the
lahar a few years after it occurred. The whole area paved
by the mud, rock hard by the time I saw it a few years
later. However, if any good came from this event, it was
that it opened many people's eyes around the world to
the dangers posed by volcanoes and the relatively simple
solutions to preventing tragedies like this.

Fumaroles – a vent in the ground where
steam and gases from volcanic activity
escape
– Carbon dioxide escaping from fumaroles can
be dangerous
Liquid Emissons
Thin, runny magma is more likely than
thick magma to remain fluid enough to
flow as lava.
 Lava causes fewer deaths than other types
of volcanic emissions because of its slow
rate of flow.


Pahoehoe lava flow
– Fast flowing lava
– Has a shiny surface and an appearance similar
to twisted rope when hardened

‘A’a lava flow
– Slow flowing lava that has a rough broken
surface with sharp edges when hardened

Pillow lava flow
– Forms under water
Solid Emissions

Solidified lava; also called pyroclastic
materials
– Ash – tiny, angular, glassy fragments
– Tephra – an accumulation of loose ash
– Cinders – pieces of solidified magma a little
larger than ash
– Bombs – masses of lava that solidify while
flying through the air
Classifying Volcanoes

There are three major ways to
classify volcanoes.
– Structure
– Activity
– Explosivity
Structure
Shield Volcano
 Cinder Cone Volcano
 Composite Volcano

Shield Volcano
Emits mostly lava in quiet eruptions
 Dome shaped with relatively flat slopes
 Broadest type of volcano

Examples of Shield Volcanoes
Hawaiian Islands
 Mauna Loa – the world’s largest active volcano
 Mauna Kea - greatest actual height of any
mountain on earth
 Surtsey – formed a new island in 1963

– Now supports plant life and animals

Olympus Mons on Mars
– Largest volcano in the solar system
Island of
Hawaii
Surtsey
Olympus Mons on Mars
Olympus Mons, Mars
Maxwell Montes, Venus
Mt. Everest, Earth
Cinder Cone Volcano
Emits mostly cinders, ashes, and bombs
 Relatively steep slopes
 Results from a single, short eruptive
period

– Typically small

Paricutin in Mexico
Paricutin
Composite Cone Volcano
Emits lava and solid debris in alternately
quiet and explosive eruptions
 Size is between shield and cinder cone
 Typical “volcano shape”
 Most volcanoes are composite volcanoes.

– Fuji in Japan
– Mt. Rainer and Mt. St. Helens in Washington
– Mt. Vesuvius in Italy
Mt. Fuji
Mt. Rainier
Classified by Historical Activity

When classifying a volcano by activity,
scientists must consider
– Time since last eruption
– Associated earthquake activity
– Nearby hot springs
– Changes of elevation within the volcano’s
crater or caldera
Active Volcano

Has erupted within historical times or
shows signs that it could erupt at any time
– Mauna Loa in Hawaii
– Vesuvius in Italy
– Mt. St. Helens in Washington
Continuous Volcano
Mt. Stromboli, Italy

The eruptions of Stromboli are seen best
at night, when chunks of lava blasted out
of the volcano trace bright red arcs in the
sky. In fact, it's such an iconic type of
eruption that geologists have named an
entire class of eruptions after Mount
Stromboli. Whenever you get a volcano
blasting out blobs of hot lava, gas, and
rocks in arcs from its volcanic vent, that's
a strombolian eruption.
Dormant Volcano

Has not erupted in historical times but
could erupt based on seismic indications
of tectonic activity beneath the volcano
– Mt. Rainier in Washington
– Mauna Kea in Hawaii
 Some of the largest and most expensive telescopes
are built on the summit.
Extinct Volcano
No historical record of eruptions
 No significant seismic activity
 Evidence of long periods of inactivity
based on erosion patterns

– Almost any supposedly extinct volcano has
the potential to erupt again.
– A volcano cannot be classified as truly extinct
until the magma chamber has been exposed
by erosion.
Classified by Explosivity

Volcanic Explosivity Index (VEI)
– A scale of 1 – 8 which estimates the explosive
power of a volcanic eruption

Mt. Tambora in Indonesia (1815)
– Category 7
– Most powerful eruption in recorded history

The Yellowstone Caldera in Yellowstone
National Park was believed to be formed
by a category 8 eruption.
Mt. Tambora
Category 7 Eruption
Classified by Location

Most active volcanoes are located in two
volcano belts
Circum Pacific Belt
Ring of Fire
Alpine – Himalayan Belt
Heated Groundwater
How is Groundwater Heated?

Geothermal gradient – the rate of
temperature change with depth
– The earth’s temperature rises between 15 50* C per kilometer of depth in the crust.
 Core temperature is approximately 5000* C
 Surface temperature is about 30* C

Magma Intrusions
Hydrothermal Processes

Hot Springs – an area where heated water
rises to the surface in a liquid state.
– The heated groundwater dissolves minerals in
the rocks that it flows through.
– The hot water cools when it reaches the
surface and the minerals precipitate.

Mud pots – hot springs that come to the
surface in volcanic ash and cinder fields
Mammoth Hot Springs
Yellowstone Park
Warm Springs, Georgia
Geysers
Thermal springs that eject water from the
ground at intervals
 For a geyser to occur there must be

– Heat, water, and a plumbing system
– Scientists think geysers are heated with
magma

Geyserite – a whitish deposit consisting of
silica dissolved from the igneous rock
through which the hot water has passed
Geothermal Energy

The internal energy of the earth
– Especially evident in areas where hot springs,
fumaroles, and geysers exist
Uses for Geothermal Energy
Resorts use hot spring for bathing and
swimming
 Heating homes and businesses
 Generating electricity

 More than 85% of the homes in Iceland are
heated by geothermal steam
 The US is the largest producer of geothermally
generated electricity.
– Enough to continually supply 130,000 homes
Difficulties in Developing
Geothermal Energy

Deciding where to explore
– Not many areas have heat close enough to
the surface to be accessible.

Obtaining funding to drill exploratory wells
– The financial risk discourages investors.