Chapter 10: Mountains and
Volcanoes
10.1: Movement of rock builds mountains
10.2: Volcanoes form as molten rock erupts
10.3: Volcanoes affect Earth’s land, air, and
water
Review t/f
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The main gases in volcanic eruptions are water vapor and
oxygen
Water vapor and carbon dioxide
Much of Earth’s volcanic activity takes place underwater along
spreading centers in the oceans
True
Lava forms as tectonic plates sink into subduction zones?
Magma forms in this process
Pyroclastic flows are dense and dangerous clouds of superhot
gases and rock fragments that race downhill during eruptions
true
Which is more dangerous to live near,
Mauna Loa or Mount Shasta?
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Mauna Loa: shield volcano, one of the most active
volcanoes on Earth, frequently produces large
amounts of lava that flow long distances
Mount Shasta: composite volcano, has erupted at
least once every 600 to 800 years for the past
10,000 years, erupts with devastating violence
Mt. Shasta erupts less often than Mauna Loa, but its
explosions are much more violent due to built-up
pressure
Volcanic gases from Mauna Loa are a constant
danger to people with breathing difficulties
Volcanoes affect Earth’s land, air, and
water
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Can knock down forests and clog rivers
Build as well as destroy – form new land
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Lava flows can form new, rich soil
Goma, in the eastern Democratic Republic of the
Congo
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Lava flow cut the city in half, destroying the homes of tens
of thousands of people
Immediate Effects
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Effects of a volcanic eruption
depend on the material ejected
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Lava flows can form new rock
Ash falls, landslides, mudflows,
pyroclastic flows, and steam
explosions:
Lava Flows: people can escape,
but it still destroys!
Volcanic Ash: weight of fallen
volcanic ash can collapse
buildings
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Contains rocks
Makes roads slippery
Clogs machinery (cars and airplanes)
Suffocate plants, animals, people
Immediate Effects
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Mudflows
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Landslides of loose rocks and soil
mixed with water
 Heat from an eruption melts ice and
snow
Ash can also mix with rivers flowing
from volcanoes
Pyroclastic flows
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a dense cloud of superhot gases and
rock fragments that races downhill
Can knock down or burn everything in
its way
Tend to follow valleys but fast-moving
flows can sweep up and over hills
Immediate Effects
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Landslides
 Rapid downhill movement of rock and soil
 May be caused by magma moving underground, an eruption, an
earthquake, or even heavy rainfall
 Can cause a tsunami!
Steam Explosions
 When magma comes near water or in contact with it
Long-term effects
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Mount Pinatubo in 1991 – threw out a lot of volcanic ash and
rock fragments
 the area gets heavy rains each year
 Mudflow formed as large amounts of rainwater mix with ash and
other loose material from the eruption
 Has destroyed the homes of more than 100,000 people since
1991
Another water source:
 Water begins to fill the volcano’s crater, the upper part of the
crater is weak, and the lake level rises
 The crater possibly collapses or overflows, emptying the lake
 In 2001 a channel was dug to divert water away to reduce
chances of a collapse
Lava cools and forms a layer of hard rock where no plants can
grow for a while, which later breaks down to form rich soil
Volcanic gases and ash affect the air
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Nearby a volcano: unpleasant odors from gases
released from magma
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Sulfur: Hydrogen sulfide gas = rotten eggs
Carbon dioxide: no color or odor
Gases released before, during, and after an eruption
Gases dangerous to breathe: lungs
In 1986, 1700 people died from a volcano at the
bottom Lake Nyos releasing a massive amount of
carbon dioxide
Pipes are now being used to release carbon dioxide
from the bottom of the lake, preventing gases from
building up
Lake Nyos in normal conditions (left) and just after the 1986
gas release (right). The sudden welling up of carbon dioxide
from the bottom of the lake brought iron to the surface, which
oxidized, creating the brown rust color.
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?What are two ways a volcanic eruption can result in damage to areas
hundreds of kilometers away?
Heavy ash falls or tsunamis
Why can volcanic ash be dangerous for years after an eruption?
Ash can mix with other loose materials and rainwater or floodwater to
create dangerous mudflows
Describe how volcanic eruptions affect Earth’s surface
 What are four kinds of events that can happen during a volcanic
eruptions?
Lava flows, mudflows, pyroclastic flows, steam explosions
Explain: How do volcanic gases affect the atmosphere: How do
volcanic gases aid ash in blocking sunlight?
They lift ash high above an erupting volcano where winds can spread
the ash and keep it suspended in the atmosphere, so it blocks
sunlight
Describe two ways sulfur dioxide can affect the atmosphere
By forming acid rain and by forming a haze that blocks sunlight
Volcanic activity affects water
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Ex: Yellowstone National Park: hot springs
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Heated water flowing to the Earth’s surface
Sit in a huge caldera
Hot spring’s heat comes from a hot spot under the
North American plate
Hot Springs, Geysers, and Fumaroles
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Hot springs are usually in areas where magma or
hot rock is near Earth’s surface
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Usually hot water flows into a calm pool
Geysers are a type of hot spring where water shoots
into the air
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Water collects in an underground chamber
It then erupts through a narrow channel
Old Faithful in Yellowstone: erupts every 35 minutes to 2
hours
Hot Springs, Geysers, and Fumaroles
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Beneath Iceland: ocean spreading center
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Magma rises as plates pull apart
Hot underground water is used as an energy
source
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Geothermal spa!
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The steamy waters are part of a lava formation, and full of
minerals such as silica and sulfur
Hot Springs, Geysers, and Fumaroles
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Fumarole – similar to hot spring but rather
than liquid water, it releases steam and other
gases
Changes in hot springs and fumaroles on
volcano sides indicate it may be becoming
more active
Deep-Sea Vents
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Hot springs that form at spreading centers in the ocean
Cracks in the ocean floor where cold seawater sinks to depths of
several kilometers
The sea water gets heated by hot rock and magma, then rises
again
This hot water is rich in dissolved minerals and gases from the
rock and magma
Warm water can flow gently from cracks in the floor
Some can have higher temperatures at 350C (660F) shooting out
of chimney-like vents
 This water looks black because of the dissolved minerals
 Vents are built up when the minerals cool and solidfy
Unusual organisms are found here: blind crabs and tubeworms
up to 3 m (10 ft) long
 Energy from chemicals
Volcanic gases and ash affect the air
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Sulfur dioxide + water  acids
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Volcanoes are a source of acid rain
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Can fall in rain, snow, or sleet
Rain with a large amount of acid = acid rain
So are humans – coal burning
Can damage forests, kill fish
Volcanic gases can affect worldwide weather
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Haze from sulfur dioxide, reducing temperatures
Ash can be lifted high above and far away from an erupting
volcano
Smallest ash particles remain in the air for years