Transcript Volcanoes SHOW

VOLCANOES
Volcano Basics
• Active – a volcano that has erupted
recently (geologically speaking)
• Dormant – (sleeping) has erupted
within the past few thousand years –
will likely erupt again
• Extinct – hasn’t erupted in 10’s of
thousands of years; unlikely to erupt
again
Mt. Rainier active
Mount Baker dormant
Shiprock Peak –
extinct volcano
magma: molten rock inside
the Earth
lava: magma that has
emerged on the Earth’s
surface
er
lava
magma
What makes a
Volcano Violent?
viscosity: a fluid’s
resistance to flow
high viscosity = high
resistance to flow
(THICK)
Low viscosity = low
resistance to flow
(THIN)
Nope…not
movin’
• Low viscosity magmas allow
gases to escape easily and
move easily through cracks.
• In higher viscosity lavas, gas
pressures build up and erupt
explosively.
• VIRTUAL LAB!!
Viscosity is determined by
silica content and
temperature.
The higher the silica
content, the higher the
viscosity.
The hotter the magma,
the less viscous it is.
TYPES OF VOLCANOES
1. Shield
2. Composite
3. Cinder cones
Shield Volcanoes
- largest volcanoes (tallest when
measured from the ocean floor)
- shaped like a gentle arch or
shield
-basaltic lavas (low silica
content)
- usually non-explosive
eruptions
- results in lava flows
- found in Hawaii (Mt.
Kilauea) and Iceland
lava tubes: caves left behind
after lava flows
•
Composite Volcanoes
- coned shaped; sometimes
called stratovolcanoes
- lava contains mostly
andesite or rhyolite
(higher silica content)
- more viscous
Combination of explosive activity
(pyroclastic) and lava flows
Responsible for most deaths of
any type of volcano
ex. Mount Saint Helens
Mt. Pinatubo
Mt. Fuji
Mt. Vesuvius
Mount Saint Helens, Washington State
Mt. Saint Helens, after eruption
Mount Pinatubo, 1994
Mount Fuji, Japan
Mount Vesuvius / Ruins of Pompei
Cinder Cones
- smaller volcanoes
- form quickly
-are active for a few years
and then usually go dormant
Wizard Island
ex. Paracutin, Mexico
-
1943, hole in ground
2 weeks prior, small tremors
1st day grew 10 m
By 5th day it was 100 m tall
After 2 yrs, it was 400 m tall
went quiet after 9 years
WHERE ARE
VOLCANOES?
Ring of Fire
• Area of the world where
volcanoes are common
• Outlines the Pacific
Ocean
hot spot: area of volcanic
activity independent of
lithospheric plates
ex. Hawaii
Features of Volcanoes
crater - depression found at
the top of a volcano; formed by
the explosion of the upper
portion of the cone
hot springs: water is heated
by the hot rock and reaches
Earth’s surface
geyser: heating and
circulation of water forms
a pattern (RARE!)
ex. Old Faithful
Half of the 1,000 geysers in the
world are in Yellowstone National
Park, WY (United States)
caldera: a giant crater that can
be more than 12.5 miles in
diameter
-formed by rare, very violent eruptions
-none have occurred in recorded history
(they are 1000 times more violent than
Mt. St. Helens!)
- Yellowstone caldera was formed 600,000
years ago!
Crater Lake, OR
Long Valley, CA
Aniakchak, AK
Volcanic Hazards
I. Primary Effects
II. Secondary Effects
Lava flows: eruption of
magma at Earth’s surface
Lava flows vary based on the
composition of the magma.
Pyroclastic Activity:
explosive volcanism where
tephra is physically blown
into the atmosphere
tephra: any material that
is blown out of a volcano
(mostly ash)
ash fall: huge quantities of
rock, glass and gas are blown
high into the air
-
kills vegetation
contaminate water
structural damage
jet engine “flame out”
respiratory irritation
lateral blast: explosions of
gas and ash from the side of
the volcano; destroys part of
the mountain
ex. Mt. St. Helens
Poisonous Gases
- CO2, carbon monoxide,
sulfur dioxide, and hydrogen
sulfide
- can cause acid rain;
contaminates water supply
and vegetation
Secondary Effects
lahar: debris flows and
mudflows
-volcanic debris becomes
saturated with water
-ex. Mt. Pinatubo, Philippines
Buildings buried after lahars at Pinatubo
Aerial View, Pinatubo Aftermath
Predicting Volcanoes
1. Monitoring of Seismic
Activity- often the
earliest sign
2. Thermal monitoring measuring ground
temperatures
3. Topographic Monitoring mountain may tilt and swell
before an eruption
4. Volcanic Gas Emissions changes in composition of
gases may indicates rising of
magma
5. Geologic History geologists map and date
rocks around the area