Volcanoes Unit 5 Natural Disasters. Volcano Locations Volcanoes are associated with certain plate...
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Transcript of Volcanoes Unit 5 Natural Disasters. Volcano Locations Volcanoes are associated with certain plate...
Volcanoes
Unit 5
Natural Disasters
Volcano Locations Volcanoes are associated with certain plate boundaries:
Subduction Zones Rift Valleys Mid-Ocean Ridges Hot Spots
Volcanic eruptions include any escape of lava and/or gases from the Earth.
Lava can escape from rifts, fissures and vents.
Volcano Locations
First some definitions…
Magma = molten rock inside the Earth Lava = molten rock that reaches the Earth’s
surface Volcano = the place in the Earth where magma is
transported to the Earth’s surface Vent = the place in a volcano where lava flows
Most volcanoes have more than 1 vent
Factors Affecting Eruptions
Magma compositionViscosity = resistance to flow (ex: maple syrup = high
viscosity)Explosive eruption = more viscousMore silica in magma = greater viscosity
Magma temperature Greater heat = less viscous
Factors Affecting Eruptions Dissolved Gases
Gases in magma = force to eject molten rock As magma gets closer to surface --> pressure in magma is
reduced Dissolved gases released suddenly
Fluid basaltic magmas = gases bubble and escape easily Quiet eruptions (ex: Hawaii)
Highly viscous magmas = slow movement of gases Gases collect in bubbles and increase in size Explosive eruptions (ex: Mount St. Helens)
Factors Affecting Eruptions
QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.
Lava Flows
Volcanoes emit lava Hot basaltic = very fluid
10-300 meters per hourHardens = form smooth skin that wrinkles as it moves
= pahoehoeAa = rough, jagged blocks with sharp edges
Silica-rich lava = slow
pahoehoe
aa
Volcanic Particles During volcanic eruptions,
many rock fragments are blown into the air
Dust = smallest of volcanic debris (less than .25 mm)
Usually pushed up into the atmosphere
Ash = next biggest (.25 mm- 5 mm)
Can reach places on the other side of the globe from the volcano
ash
Volcanic Particles Cinders = small (golf ball sized) particles thrown from the volcano
Usually liquid when they leave the volcano but solid when they land Bombs = large cinders to blocks of rock (few cm – several meters)
Liquid when they leave the volcano, harden as they travel
bombs
Anatomy of a Volcano
Volcano Types:
Cinder Cone Composite (or Stratovolcano) Shield
QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.
Cinder Cones: form by explosive eruptions of volcanic material the size
of cinders into the air Settles around the volcano’s vent to form steep, loosely arranged
sides of the cone Narrow base and steep sides Not really tall Single eruption that lasts a few weeks-few years
Eruption ends = magma in pipe solidifies and it won’t erupt again
examples include: Pari’cutin, Mexico
Cinder Cones (cont):Pari’cutin, Mexico
Composite Cones: Built up of alternating
layers of pyroclastic deposits & lava explosive eruption, lava blanket, explosive eruption, lava blanket, and so on.
Generate viscous lavas that travel only short distances
Composite/Stratovolcano (cont.): When a violent eruption
occurs, tephra is ejected at very high speeds in an event known as a pyroclastic flow.
Explosive eruption Most located in the Ring of
Fire Usually capped with a
crater Classic looking volcanoes Examples: Mt. St. Helens,
Mt. Vesuvius
Composite/Stratovolcano (cont): Mt. St. Helens
During: After:
CompositeMt. Mayon, Philippines
Mt. Agua, Guatemala
Composite Cones--Dangers Pyroclastic flows = hot
gases, glowing ash, rock fragments Sometimes flows can go
downslope very quickly
Mount St. Helen’s Pyroclastic Flow
Composite Cones--Dangers Can make mudflows =
lahars Volcanic debris saturated
with water Consistency of wet concrete
Mt. Rainier?
Lahar on Mt. St. Helens
Ring of Fire Narrow zone that rims the
Pacific Includes Andes and
Cascades
Ring of Fire
QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.
Shield Volcano: gently-sloping dome formed from non-explosive,
runny lava Not explosive because the lava
does not have dissolved gases (like composite cones).
lava forms basalt rock form over hot spots Wimpiest of all volcanoes Examples: Kilauea, Hawaii,
Olympus Mons on Mars
Shield Volcano (cont):
Mauna Loa, Hawaii
Volcanic Landforms Caldera = big depression in a
volcano often trap rain water to form
mountain top lakes or fill-in forming islands.
Formation1. Collapse of the top of a composite volcano after eruption2. Collapse of the top of a shield volcano after the magma chamber is drained
Ex: Crater Lake, Oregon
Volcanic Landforms Lava Plateaus
Low-viscosity lava flows from fissures and cover a wide area
Ex: Columbia Plateau
Volcanic Activity Active = volcanoes that either erupt continually or periodically
Kilauea in Hawaii = continually Mt. St. Helens = periodically
Dormant = has been active in modern times but is not currently showing signs of activity Mt. Rainier
Extinct = have not shown signs of activity and have not erupted in modern times Sometimes trick us Kohala volcano, Hawaii
Where do Volcanoes Occur? Subduction Zones
Slabs of oceanic crust are pushed down into the mantle
Melting --> magma forms and migrates upward forming volcanoes
Found all over Pacific Ocean (Ring of Fire)
Where do Volcanoes Occur? Ocean-ocean subduction
Oceanic slab descends under another
Chain of volcanoes on ocean floor
Ex: volcanic island arcs = Aleutians
Where do Volcanoes Occur? Divergent Plate
Boundaries Magma from within the
mantle below rises up to erupt and fill in the space left behind as the plates move apart
New ocean crust formed At mid-ocean ridges and on
land (African continent spreading apart)
Where do Volcanoes Occur? Hot Spots (Intraplate)= place
where a lot of magma is produced, which rises to the Earth’s surface Stay stationary over long periods
of time but plates move Can be anywhere (don’t have to
be on plate boundaries) Ex: Hawaiian volcanoes Big Island of Hawaii lies above
the mantle plume
Effects of Volcanoes on Humans Houses, roads, fields covered
with ash Hard to breathe
Pyroclastic flows = can kill you Fast = can’t outrun them
Destruction of a city Produce rich soils for farming Beauty
Climate Effects of Volcanic Eruptions Indirect role in reducing ozone levels
Short lived Emit CO2 which enhances global
warming Offset by global cooling caused by
particles that block out sunlight (haze effect)
Enhance haze effect Block sunlight, lower temps.
Billowing eruption plume being
carried in a westerly direction
Effects of Volcanoes on Earth’s Systems
Biosphere Killed by lava flows, pyroclastic
flows, gases, tsunamis Die from famine, forest fires,
earthquakes Aquatic life = increased acidity,
change in temperature Influence bird migration, flying
ability, feeding activity
Effects of Volcanoes on Earth’s Systems
Hydrosphere = Increase temperatures Falling ash contaminates streams and ponds
Can be water supply for many people Eruptions can result in floods Create tsunamis
Lithosphere Create new islands and land Create mineral deposits Destroy habitats and crops Create beautiful landscapes