volcanoes! - mr. celia's science...
TRANSCRIPT
Volcanoes
• A volcano is a
mountain that
forms when molten
rock is forced to
the earth’s surface.
How many are there and how often do they
erupt?
• There are about 1500 volcanoes that are known to have erupted within the last 10,000 years.
• Normally, eruptions at volcanoes are irregular.
• Some eruptions can be quite regular. For example: Mt. Stromboli in Italy erupts every 15 min or so, for the last 1000 years.
• Arenal in Costa Rica is currently continuous.
• Volcanic Structure
• The
Roman
God
Vulcan,
causing an
eruption.
Important Reminder:
• Molten rock under
the ground is called
MAGMA
• Molten rock at the
surface of the earth
is called LAVA
What does a volcano look like
inside?
• All volcanoes share the same basic features.
They all form around ‘vents’ of magma that is
released to the earth’s surface.
Vents
Magma Chamber
Crater
• Types of Eruptions
How does a volcano erupt?
• Volcanoes erupt either in an explosive
manner or non explosive manner.
Explosive Eruptions: • Hot debris and gasses shoot
out of the volcano at supersonic speeds.
• Little bits of magma are blown out and harden into rock as it flies through the air.
• Larger rocks and particles then rain down on and around the volcano.
Explosive Eruptions
• Smaller bits of volcanic dust can remain in the atmosphere for years.
• If the pressure inside is great enough, the entire top of the volcano can be blown apart.
• With explosive eruptions, volcanoes may actually shrink instead of grow after the eruption is over.
Non explosive
eruptions • Lava gradually pours
out of a volcano over a
long period of time.
• This slowly builds up
the size of the volcano
over thousands of
years.
• Some of the largest
mountains on earth are
made this way.
What erupts from a volcano?
• Explosive volcanoes eject pyroclastic materials which are usually rock fragments.
• Non Explosive eruptions are normally lava flows.
• Most volcanoes alternate between both pyroclastic materials and lava flows.
What are pyroclastic materials? • The term "pyroclastic" – is derived from the Greek
words pyro (fire) and klastos (broken)
• Pyroclastic materials are the debris formed in the explosive eruptions of volcanoes.
• Consists of solidified chunks of magma and lava and the exploded remains of the surrounding rocks.
• Small, fine grained pyroclastic material is called Volcanic Ash.
• Larger sized pyroclastic fragments are called Lapilli, blocks, or bombs.
Volcanic Ash
Used to
show scale
• Pyroclastic Flow: High-speed avalanches of
hot ash, rock fragments, and gas.
• They move down the sides of a volcano during
explosive eruptions or when the steep edge of a
dome breaks apart and collapses.
• They can reach 15000F and move at 100-150
miles per hour.
• They are capable of knocking down and burning
everything in their path.
• Pyroclastic flow sweeps down the side of Mayon Volcano, Philippines, during an explosive eruption on 15 September 1984. Note the ground-hugging cloud of ash (lower left) that is billowing from the pyroclastic flow and the eruption column rising from the top of the volcano.
• Types of Volcanoes
Three types of volcanoes
• Shield, cinder cone, and
composite are all types
of volcanoes.
Each volcano is formed in
a slightly different way.
Shield Volcanoes
• These types of volcanoes are built out of
layers of lava from repeated non explosive
eruptions.
• Shield volcanoes usually have very gently
sloping sides an a large base.
• Although they are not very steep, these
volcanoes can be enormous.
• Mauna Kea in Hawaii is a shield volcano.
Shield Volcano
• The Hawaiian Islands are composed of linear chains of shield volcanoes.
• Kilauea and Mauna Loa are two of the world's most active volcanoes.
• As Mauna Loa, the largest of the shield volcanoes (and also the world's largest active volcano), projects 13,677 feet above sea level, its top is over 28,000 feet above the deep ocean floor.
Cinder Cone Volcanoes
• Cinder cone volcanoes are small and made up of
pyroclastic material deposited by mildly explosive
eruptions.
• These volcanoes are usually very steep with a
narrow base.
• Cinder cone volcanoes erode quickly because
the pyroclastic material is not cemented together
by lava.
• Cinder cones are the simplest type of volcano.
• As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone.
• Most cinder cones have a bowl-shaped crater at the summit and rarely rise more than a thousand feet or so above their surroundings.
• There are many cinder cones in Western North America.
• Cinder cone volcanoes often form on the sides, or flanks, of Shield and Composite volcanoes.
• A flank eruption on Mt. Etna, Italy
Famous Cinder Cone Volcanoes
• Parícutin, in Mexico.
• Sunset Crater, Arizona
• Vulcan's Throne, Arizona
• Monte Nuovo, Italy
• Lava Butte in Newberry National Volcanic
Monument, Oregon. (Photo)
Typical Cinder Cone
Cinder Cone Volcano
• The Birth of
a Volcano
Where did that come from?
• In 1943 a cinder cone started growing on a farm near the village of Parícutin in Mexico. Explosive eruptions caused by gas rapidly expanding and escaping from molten lava formed cinders that fell back around the vent, building up the cone to a height of 1,200 feet.
• The last explosive eruption left a funnel-shaped crater at the top of the cone. After the excess gases had largely dissipated, the molten rock quietly poured out on the surrounding surface of the cone and moved downslope as lava flows. This order of events--eruption, formation of cone and crater, lava flow--is a common sequence in the formation of cinder cones.
• During 9 years of activity, Parícutin built a prominent cone, covered about 100 square miles with ashes, and destroyed the town of San Juan. Geologists from many parts of the world studied Parícutin during its lifetime and learned a great deal about volcanism, its products, and the modification of a volcanic landform by erosion.
• Parícutin Volcano, Mexico, is a cinder cone rising approximately 1,200 feet above the surrounding plain. It is a subduction zone volcano.
• The church at Paricutin. Photograph by K. Segerstrom, U.S. Geological Survey, 1948.
• Paricutin was the first volcano born in the
20th century. It erupted for nine years. By
the time Paricutin went dormant in 1952, it
had formed a 424-meter cinder cone in the
highlands southwest of Mexico City.
• The volcano of Paricutin now bears the honor of being listed as one of the world's 7 natural wonders. It holds the distinction of being the only volcano on the planet born in modern times. Eruptions from volcanoes are commonplace occurrences but the birth of an entirely new volcano is genuinely rare.
Composite volcanoes • Composite volcanoes are also called
stratovolcanoes.
• These are the most common type of
volcanoes.
• They form from a combination of
explosive and non explosive eruptions.
This gives them layers of pyroclastic
materials and lava flows.
• They have broad bases and steep
summits.
Composite Volcanoes Facts
• Most composite volcanoes have a crater at the summit which contains a central vent or a clustered group of vents.
• Lavas either flow through breaks in the crater wall or issue from fissures (cracks) on the flanks of the cone.
• Lava, solidified within the fissures, forms dikes that act as ribs which greatly strengthen the cone.
Mt. Shasta
Inside a Composite
Composite Volcano
Notable Composites
• Some of the most conspicuous and beautiful mountains in the world are composite volcanoes, including – Mount Fuji in Japan,
– Mount Cotopaxi in Ecuador,
– Mount Shasta in California,
– Mount Hood in Oregon,
– Mount St. Helens and Mount Rainier in Washington.
– Mount Vesuvius, Italy.
Irazu Volcano in Costa Rica
• States of Volcanic Activity
There are many differing definitions for what
a volcano is doing…..
• For our purposes, we will use these definitions:
• Active: a volcano that currently shows any sign of activity, including seismic (tremors and earthquakes) and gas emissions.
• Examples: Mt. Stromboli, Italy, Mauna Loa, Hawaii
Mt. Stromboli, Italy
• A dormant volcano has erupted in historic times (last 10,000 years) but currently shows no sign of activity.
• Example: Mt. St. Helens, WA can be dormant for 1000s of years between eruptions. It was dormant since 1857 before it erupted on 18 May, 1980.
• An extinct volcano is one that is currently not active nor dormant and is unlikely to erupt again.
• Example: Mt. Kilimanjaro in Africa, old volcanoes on the Hawaiian island of Oahu
Dikes and Sills
Dikes
• A dike is a flat vein of
solidified magma cutting
across layers of older
rocks.
• Dikes form when molten magma seeps
into cracks in the surrounding rock.
• The point where a dike reaches the
surface and erupts lava can be called a
vent.
• Dikes in the
Black Canyon of
the Gunnison
National Park,
Colorado, USA
• Magmatic dikes radiating from West
Spanish Peak in Colorado
Sills
• A Sill is like a
dike, that is in
between layers of
rocks, not cutting
through them.
Sills
• Where do volcanoes Form?
Where do volcanoes Form?
• Volcanoes form anywhere magma comes to the earth’s surface.
• Subduction zones and the mid-oceanic ridge are both places we find volcanoes.
• Sometimes, magma ‘burns’ a hole in the middle of a plate. This is called a Hot Spot. The Hawaiian Islands are all Hot Spot Volcanoes.
• Map of the Island of Hawai`i
Mid-Oceanic Ridge
• The global mid-ocean ridge system is the largest single volcanic feature on the Earth, encircling it like the seams of a baseball.
• Here the Earth’s crust is spreading, creating new ocean floor and literally renewing the surface of our planet.
• The mid-ocean ridge consists of thousands of individual volcanoes or volcanic ridge segments which periodically erupt.
The Mid-
Atlantic
ridge
• The majority of the world's active
volcanoes above sea level are located in a
geographic belt of subduction zones called
the Ring of Fire.
• The pacific plate is getting subducted by
most other plates.
• When a Volcano finally dies…..
• When a volcano becomes dormant,
erosion begins to destroy the cone.
• When the cone is eroded away, all that is
left are the solidified magma chamber and
main vent, and smaller vents.
• The remains of the magma chamber and
main vents are called volcanic necks and
the smaller vents make dikes and sills.
Extinct Volcanoes
Volcanic Necks
• A volcanic neck is a cylindrical-shaped landform standing above the surface created by magma solidifying in the vent of a volcano. Erosion of the sides of the volcano exposes the neck.
• In other words, after a volcano has become extinct, the central core solidifies and over millions of years becomes exposed as the outer portion of the volcano erodes away.
Devil’s Tower,
WY, is another
example of a
volcanic neck.
Blue Hills, MA The Blue
Hills are the
remains of
volcanoes
that last
erupted
around 440
million years
ago.
Granite on top of Blue Hills
weathered by glacial activity
• The Blue Hills lay the foundation for the many types of igneous rock found in Eastern Massachusetts.
• Quincy Granite, used to build many buildings around New England, was formed by the magma chamber of Blue Hills cooling and solidifying slowly over time.
• Unlike Devil’s Tower
and Shiprock, Blue
Hills has been
subject to repeated
glacial activity and
the volcanic neck
has been worn down
over time.
• A dike
radiating
away
from
Shiprock.
• A. Magma, rising upward through a conduit, erupts at the Earth's surface to form a volcanic cone. Lava flows spread over the surrounding area.
• B. As volcanic activity continues, perhaps over spans of hundreds of years, the cone is built to a great height and lava flows form an extensive plateau around its base. During this period, streams enlarge and deepend their valleys.
• C. When volcanic activity ceases, erosion starts to destroy the cone. After thousands of years, the great cone is stripped away to expose the hardened "volcanic plug" in the conduit. During this period of inactivity, streams broaden their valleys and dissect the lava plateau to form isolated lava-capped mesas.
• D. Continued erosion removes all traces of the cone and the land is worn down to a surface of low relief. All that remains is a projecting plug or "volcanic neck," a small lava-capped mesa, and vestiges of the once lofty volcano and its surrounding lava plateau.
• Notable Volcanoes
Notable Volcanoes
Mt. Etna, Italy erupting in 2002
The 79 A.D. eruption of Vesuvius was the first
volcanic eruption ever to be described in detail.
From 18 miles (30 km) west of the volcano,
Pliny the Younger, witnessed the eruption and
later recorded his observations in two letters.
He described the earthquakes before the
eruption, the eruption column, air fall, the
effects of the eruption on people, pyroclastic
flows, and even tsunami. Volcanologists now
use the term "plinian" to refer to sustained
explosive eruptions which generate high-
altitude eruption columns and blanket large
areas with ash. It is estimated that at times
during the eruption the column of ash was 20
miles (32 km) tall. About 1 cubic mile (4 cubic
kilometers) of ash was erupted in about 19
hours.
Mount Vesuvius
• Mt. Vesuvius as seen from the ruins of Pompeii, which was destroyed in the eruption of AD 79. The active cone is the high peak on the left side; the smaller one on the right is part of the Somma caldera wall.
• About 10 feet (3 m) of tephra fell on Pompeii, burying everything except the roofs of some buildings. The city was abandoned and its location forgotten. In 1595, excavations discovered artifacts at Pompeii and centuries of pillaging followed. Archeological excavations began in the mid-nineteenth century. Now, much of Pompeii has been excavated and it has revealed much about how people lived during that time (and died during the eruption). There are numerous molds of people in their final moments. The mold of a dog is shown in the above photo. The poor animal was chained to a post and struggled for hours before finally succumbing to the ash.
Mt. Saint Helens
• Mt. St. Helens is an excellent example of a
volcano with an explosive eruption.
• Mt. St. Helens had not erupted in over 123 years
when she started showing signs of instability –
earthquakes and smoke rising out of fissures in
March of 1980.
• In April, a huge bulge started to form on the side
of the mountain. This was a sign of building
pressure. The bulge grew 5 ft per day.
• On May 18, 1980 Mt. Saint Helens finally
erupted.
• The eruption caused the largest landslide
in history – within seconds the mountain’s
height dropped more than 1300 feet!
• Burning gasses moving at 670 miles per
hour burned away forests up to 6 miles
away.
• The heat from the blast melted away all of
the snow on the mountain causing horrific
mud flows that carried away or buried
everything in its path – including homes.
Before:
After
57 people died in this eruption.
• Eruption of Mount St. Helens volcano, 1980. The volcano, located in the state of Washington, rose to a height of
9,677 feet and was a perfect cone shape before the eruption. The explosion caused the breaking away of the
uppermost 1,300 feet, and resulted in the largest landslide in recorded history.
This car was more than 7 miles from the
mountain.
These mailboxes are buried in mud
flows…35 MILES away from Mt. St. Helens
The new Landsat 7
satellite is now taking
high resolution images
of the Earth. This 1999
press release picture
shows Mt. St. Helens.
The green is forest and
fields, the white is
glaciers and snow, and
the grey shows areas
destroyed by flowing
ash in the 1980's
eruption that have still
not recovered their
vegetation covering.
Spirit Lake is still partly
covered by floating
logs. Image by EROS
Data Center, Sioux
Falls, SD.
Yellowstone Supervolcano
• Yellowstone National Park is famous for its
geysers, but actually contains one of the
largest volcanoes on Earth.
• The volcano is classified as a caldera
volcano, one that forms after land
collapses and sinks after a volcanic
eruption.
• Yellowstone is one of only ten
supervolcanoes on Earth.
• It is a hotspot volcano.
• It is so large it can only be
seen from the air.
• Yellowstone experiences
more than 2000 earthquakes
each year.
• Yellowstone last erupted
640,000 years ago,
covering half of North
America with pyroclastic
ash that caused the
extinction of thousands of
plants and animals.
• Dust remained in the
atmosphere for over a
year, lowering global
temperature about 2
degrees.
• Area covered by
pyroclastic flow
640,000 years
ago.
• When it did erupt, the Mountains above and
around Yellowstone sunk thousands of feet into
the magma chamber forming the current
caldera.
Will Yellowstone Erupt again?
• No one is really sure. We do know the more
non-explosive eruptions it has, the better off we
are.
• If it does erupt, life on Earth will drastically
change.
The End