Download Volcano Notes

Volcanoes
1
Volcanoes
around the
world
Volcanoes per Continent
So
As
ia
Eu
ro
pe
Af
r
An ica
ta
rc
tic
a
ut
h
Au
st
ra
l
i
Am a
N
er
or
ic
th
Am a
er
ica
250
200
150
100
50
0
Australia
South America
North America
Asia
Europe
Africa
Antarctica
2
INTRO VIDEO
3
What is a volcano?
vent
cone
conduit
• A volcano is a vent
or 'chimney' that
connects molten
rock (magma) from
within the Earth’s
crust to the Earth's
surface.
• The volcano includes
the surrounding
cone of erupted
magma material.
chamber
4
Volcano vent
5
Eruption Cloud
Eruption Column
Tephra
Landslide
Acid Rain
Pyroclastic Flow
Dome
Pyroclastic
Flow
Lahar
Lava
http://volcanoes.usgs.gov/Hazards/What/hazards.html
6
• Steep-walled depression around a
volcano’s vent
• Formed as lava flows out of vent,
quickly cools, hardens and sinks
7
8
9
• DOME
•Build up
of quiet
lava
10
• Hot, molten rock (magma) is buoyant (has
a lower density than the surrounding
rocks) and will rise up through the crust to
erupt on the surface though an opening
called a vent.
•Same principle as hot air rising, e.g.
how a hot air balloon works
11
• Viscosity = how resistant a fluid is to flow.
• High viscosity = thick, does not flow well = explosive
eruption
• Low Viscosity = runny = quiet eruption
• What determines the viscosity of a volcano’s lava?
1. Composition of magma (what the magma is
made of)
• High silica—high viscosity
• Andesitic lava
• Low silica content – low viscosity
• Basaltic lava
12
2. Temperature of Magma
• Hotter lava tends to be less viscous
• Cooler lava tends to be more viscous
3. Amount of gas in magma
• Mostly water vapor and carbon dioxide (CO2)
• Large amounts of gas and a high viscosity (sticky) magma will
form an explosive eruption!
• Think about shaking a carbonated drink and then
releasing the cap.
• Small amounts of gas and (or) low viscosity (runny) magma
will form an effusive eruption
• Where the magma just trickles out of the volcano
(lava flow).
13
The Nature of Volcanic Eruptions
Factors Affecting Eruptions
 Dissolved gases
• Violence of an eruption is related to how easily
gases escape from magma
-Gases escape easily from fluid magma = less
violent eruption
-Gases can’t as easily escape from Viscous
magma - produces a more violent eruption.
• Have severe
environmental
and climatic
effects
• Hazardous!!!
Mt. Redoubt
Above: Large eruption column
and ash cloud from an
explosive eruption at Mt
Redoubt, Alaska
15
Effusive Eruptions
• Effusive eruptions are
characterized by outpourings
of lava onto the ground.
Hawaii
Courtesy of www.swisseduc.ch16
WHERE DO VOLCANOES OCCUR?
• Form in one of three places
–Divergent plate boundary
–Convergent plate boundary
–Hot spot
17
Divergent Boundaries
• Plates separate (move apart) and
magma flows up from the rifts.
• Can rise above sea level to form
islands
• Ex: Mid-Atlantic Ridge, Iceland
18
Divergent Plate Boundary
19
Thick ash poured from Iceland Eyjafjallajokull
volcano when the Moderate Resolution
Imaging Spectroradiometer (MODIS) on
NASAÕs Aqua satellite acquired this image on
April 19, 2010, blowing south and then
turning east to the United Kingdom. The ash
cloud consists of fine particles of pulverized
rock, and potentially can cause a catastrophic
hazard to aviation. UPI/NASA
20
Convergent Boundaries
• Plates move together
• Creates a subduction zone where
several volcanoes may form
• Ex. Ring of Fire
21
ANIMATION OF OCEANIC-OCEANIC
COLLISION
• http://www.phschool.com/webcodes10/index
.cfm?fuseaction=home.gotoWebCode&wcpref
ix=cul&wcsuffix=3101
22
23
Pacific Ring of Fire
24
Hot Spots
• Areas away from plate boundaries
where magma is forced to the
surface
–Ex: Hawaii, Yellowstone
25
What causes volcanoes?
Hot Spots
26
Hawaiian Hot Spot
27
• The Yellowstone hot spot has been
active for at least 15 million years,
producing a chain of geysers and
other volcanic features along the
Snake River Plain (US) that extends
from Wyoming to the Idaho-Oregon
border.
Video
28
29
30
STOP
31
•
•
•
•
•
•
Courtesy of www.swisseduc.ch
Pyroclastic flow
Lahars/Mud flows
Pyroclastic fall
Lava flow
Noxious Gas
Earthquakes
32
• PYROCLASTIC
FLOW
– A highly heated
mixture, largely of
ash and pumice
fragments,
traveling down the
flanks of a volcano
or along the
surface of the
ground
33
Direct
measurements
of pyroclastic
flows are
extremely
dangerous!!!
34
35
Mayon Volcano, Philippines
36
Mt. St. Helens, Washington
37
Unzen Volcano, Japan
38
• LAHAR
•Debris flow on the
slopes of
volcanoes that
result when
unstable layers of
ash and debris
become saturated
with water and
flow down slope
•Usually follows a
stream channel
VIDEO
39
40
• If it doesn’t flow out of the volcano, it
gets blasted from the volcano. These
blasted pieces can range in size.
41
• Tephra is a general term for all
fragments of volcanic rock and lava that
are blasted into the air by explosions or
carried upward by hot gases.
• Such fragments range in size from less
than 2 mm (ash) to blocks the size of
houses.
• Pyroclastic material (or pieces shot from the
volcano) are classified by their sizes.
42
• There are 4 main types/sizes ejected from explosive
eruptions:
• Volcanic blocks: Solid chunks of rock blasted
from the volcano, they are basically chunks of the
volcano top.
• Volcanic bombs: Large blobs of magma that
harden in the air. They often form tear-drop
shapes as they fly through the air. They are larger
than 64mm in diameter.
43
What Erupts from a Volcano?
Volcanic blocks
Volcanic bombs
44
•Lapilli (La pill ee): Meaning “little stones”
in Italian, these are pebble-like pieces
that range from 2mm to 64mm.
•Volcanic Ash: Particles that are less than
2mm in diameter. Ash forms when gases
force magma to explode into tiny pieces.
45
What Erupts from a Volcano?
Lapilli
Volcanic ash
46
Day Turns to Night
Roofs May collapse
47
HOW DO VOLCANOES AFFECT
THE EARTH?
Flows and Fallouts
• Hot ash can flow really
quickly
•Knock down buildings
•Dam rivers (flooding/drought)
•Kill crops and livestock
•Clog water/sewage systems
Climatic Changes
•Ash & Gases can block sunlight
•Drop average global temperature
noticeably
48
Types of Lava Flow
• Type of lava flow is determined by the
viscosity of the lava
–Viscosity is determined by chemical
make-up and temperature of the lava
49
Pahoehoe: Lava with a ropelike surface texture due to
partial cooling as the lava flowed. Relatively hot, low
viscosity lava.
50
Aa: Blocky, rough lava flow. Due to high
viscosity lava that flowed pushing
chunks of solid and semi-solid blocks.
www.volcanovideo.com/Movies/p8vdclp.htm
51
52
Pillow lava: The result of lava erupting
underwater. The water causes rapid
cooling and results in bubble like pillows.
53
Types of Volcanoes
1.
Shield
– Lava quietly flows from vent
– Mountain covers large area, is dome-shaped
and gently sloping
– Shield Volcanoes are built by many layers of
runny lava flows
54
Shield Volcano Continued….
–This is caused by the very fluid, basaltic
lava which can't be piled up into steep
mounds
–Ex. Mauna Loa in Hawaii
55
Mauna Loa
• Earth’s largest volcano
56
Types of Volcanoes (cont.)
2. Cinder cone volcano
– Small volcanic cones made from its own
pyroclastic material.
– Has a steeper slope with a narrower base.
– They often erode quickly because they are not
cemented down by lava.
– among the most common volcanic landforms
found in the world.
57
• Cinder cones are built from lava fragments
called cinders. The lava fragments are ejected
from a single vent and accumulate around the
vent when they fall back to earth.
• The cones usually grow up in groups and they
often occur on the flanks of strato volcanoes
and shield volcanoes.
58
Paricutin, Mexico
• It was born in February 20, 1943 in a corn
field and grew to 300 feet in 5 days.
59
PARICUTIN, MEXICO
60
Outside of St. George, UT
Photo by: Ms. Conley
61
Types of Volcanoes (cont.)
3. Composite (Stratovolcanoes)
– Strato-volcanoes are mainly found along
subduction zones
– Forms mountain large and cone-shaped with
steep sides
– Violent eruption sends up volcanic bombs,
cinders and ash
– Quiet volcanic flow follows explosion
– Alternating layers of rock fragments and lava
form mountain
62
• Between eruptions they are often so
quiet they seem extinct
• Composite volcanoes usually erupt in an
explosive way.
– This is usually caused by viscous magma.
– When very viscous magma rises to the
surface, it usually clogs the craterpipe, and
gas in the craterpipe gets locked up.
– Therefore, the pressure will increase
resulting in an explosive eruption.
• Ex: Mt. St. Helen’s, Washington
63
64
Mt. St. Helen’s Before and After
65
• Mt. Saint Helens Video
66
67
Mt. Fuji, Japan
68
69
Prediction of Danger
• Because volcanoes can devastate
enormous areas, including people,
good prediction of eruptions and
their effects is very important.
• What are believed to be the most
dangerous volcanoes can be
continually monitored by accurate
measurements
70
• The most important methods and
instruments used to predict an eruption are:
–Seismographic monitoring
• Rising magma causes moderate earth
tremors,
• When the magma is approaching the
surface the frequency and intensity of
the tremors will increase
71
• Tiltmeters
Rising magma within a volcano often causes
ground deformation. The ground deformation
is measured by tiltmeters.
• Surveillance by satellite
Global Positioning System (GPS) is used to
monitor changes in shape of the ground ,
including those around volcanoes, which
might pinpoint future activity.
72
73
stop
74
Discovery Volcano Video
Streaming…
75