Volcanoes (examples throughout slides). Vulcanism/volcanism. What constitutes an active volcano? Lava, pyroclastic material. Types of eruptions. Structures associated with extrusive volcanism. Volcanic peaks. Felsic = composite volcano/stratovolcano, lava dome. Mafic = shield volcano, cinder cone. Caldera. Volcanic Neck. Flood basalts. Hazards associated with extrusive volcanism. Volcanic blast. Earthquakes. Debris flows. Mudflows, lahars. Eruption column and ashfall. Pyroclastic flows. Lava flows. Volcanic gases. Structures associated with intrusive volcanism. Pluton. Batholith, laccolith, stock, dike, sill, vein.

1. VolcanoesVolcanoes
Earth’s Interior in Action!Earth’s Interior in Action!

2. 22
• Volcanism:Volcanism:
all phenomena associated with the origin andall phenomena associated with the origin and
movement of molten rockmovement of molten rock
⇐A volcanologist
geared up for work

3. 33
What Constitutes AnWhat Constitutes An
“Active” Volcano?“Active” Volcano?
• Not fully agreed upon among scientists
• Intervals between eruptions may be thousands
of years
• On land, close to 1500 have erupted in the past
10,000 years
– Millions, if you count undersea eruptions
• Over a thousand active magma systems have
been identified on land
• An accurate count of the world’s volcanoes
remains elusive

4. Chaiten Volcano
(southern Chile)
May 3, 2008—Chaiten volcano erupts May 2nd and thousands flee; ash from the
volcano reaches Esquel, Argentina; last recorded eruption: over 9000 years ago
(7420 BC ± 75 yrs)

5. 55
What’s that stuff on the ground?What’s that stuff on the ground?
• Lava
– Magma that makes it to the
surface
• Pyroclastic material
– When lava erupts into the air
and cools quickly, it can form
material the size of ash up to
large rocks
– Any of this solidified lava
“spew” is called pyroclastics
(pyro = fire; clast = rock)

6. 66
EruptionsEruptions
• Whether a volcanic eruption is explosive
or mild depends on the type of magma
chemistry that is involved.
– Felsic = explosive
– Mafic = mild

7. 77
Structures Associated WithStructures Associated With
Extrusive VolcanismExtrusive Volcanism
• Volcanic peaks
• Caldara
• Volcanic neck
• Flood basalt

8. 88
Volcanic PeaksVolcanic Peaks
• The type of peak that forms depends on
the type of magma
– Felsic
• Forms composite (strato) volcanoes
– Magmas don’t flow far
– Tall, steep-sided cones
– Mafic
• Forms shield volcanoes
– Magmas flow for long distances
– Broad, gently-sloping cones

9. 99
Composite VolcanoComposite Volcano
(also called a Stratovolcano)(also called a Stratovolcano)
• Felsic magma, tall, steep-sided cone formed of
alternating layers of lava flows and pyroclastic
material
Mount Mayon
Philippines, Island of Luzon, province of Albay,
Bicol region, 15 km NW of Legazpi City

10. 1010
Shield VolcanoShield Volcano
• Mafic magma (basaltic), gentle slope (looks like
a warrior’s shield laid on the ground)
Mauna Loa Shield Volcano

11. 1111
Other Types of Volcanic PeaksOther Types of Volcanic Peaks
• Lava Dome—Formed from felsic magmas,
like a bulge on the surface
– Common where previous felsic eruptions have
occurred
– Material not well fused together (easily eroded)

12. 1212
Lava domeLava dome
New lava dome forming inside Mount St. Helens

13. 1313
Other Types of Volcanic PeaksOther Types of Volcanic Peaks
• Cinder Cone
– Usually less than 150 ft. high
– Associated with flood basalts and shield
volcanoes
– Frothy, (usually) mafic magma under high
pressure at a narrow vent
– Tephra rains around the vent, forming small,
rounded volcanoes made of ash and cinders

14. 1414
Cinder conesCinder cones
Wizard Island—Crater Lake, OR

15. 1515
CalderaCaldera
• Collapsed and/or
exploded volcanic
peak, producing a
crater

16. Long Valley Caldera in California

17. 1717
Volcanic NeckVolcanic Neck
((Shiprock, NM)Shiprock, NM)
• Solidified magma within the “neck” of a volcano
• Surrounding material may later be eroded away,
leaving a tall, standing structure of igneous rock

18. 1818
Flood BasaltsFlood Basalts
(also called Fissure Eruptions)(also called Fissure Eruptions)
• No dome or cone-shaped structure
• Magma flows out of breaks in the crust, usually
in high volume, in layers that may be hundreds
of feet deep and thousands of miles wide
– Deccan Plateau in India
• 200,000mi2
– Columbia Plateau, crossing WA, OR, and ID borders
• 50,000mi2

19. 1919
Flood BasaltFlood Basalt
Columbia Gorge, along the Columbia River in the
Cascade Mountains of Washington and Oregon

20. 2020
Hazards Associated withHazards Associated with
Extrusive VolcanismExtrusive Volcanism
• Volcanic blast
• Earthquakes
• Avalanches and
Debris Flows
• Mudflows and
Lahars
• Eruption column
and ashfall
• Pyroclastic flows
• Lava flows
• Volcanic gases

21. 2121
Volcanic BlastVolcanic Blast
(also called Blowdown)(also called Blowdown)
From Mount St. Helens:
• A 600ºF blast of rocks, ash, and gases swept
across the land at 670 miles an hour
• The force of the blast
stripped trees from hillsides 6 mi. away

22. 2222
Earthquakes and Debris flowsEarthquakes and Debris flows
• The movement of magma up through the
crust creates earthquakes
• The Mount St. Helens eruption began with
a magnitude 5.1 earthquake. The entire
north flank of the mountain broke loose in
three separate blocks, which slid down the
mountain at 100 mph.
• An avalanche of rock, ice, snow, and soil,
like this one, is called a debris avalanche

23. 2323
Debris FlowDebris Flow
• Rocks and mounds of
debris filled river
valleys for 14 miles,
as much as 600 feet
deep in some places,
damming streams
and forming new
lakes

24. 2424
Mudflows and LaharsMudflows and Lahars
• Superheated ash and
magmas melt and mix
with snow and ice, then
speed down the
volcano’s flanks
– Nevado del Ruiz,
Colombia, 1985
– Melted ice and snow mixed
with volcanic ash and mud,
sending a 130 foot (40 m)
high mud-flow down the
Lagunilla River

29. 2929
Mudflows—Mt. St. HelensMudflows—Mt. St. Helens
• …sloshing from side-to-side as it rushes through
forests and clearcuts, ripping trees, houses, and
bridges from the ground, devastating
downstream environments and communities

30. 3030
Eruption Column and AshfallEruption Column and Ashfall
• Can reach the stratosphere,
where it is transported long
distances
• Can block insolation, altering
weather and climate
• Ash and gases mix with water
in atmosphere, producing acid
precipitation
• May produce enough ash to
bury the landscape and kill
residents
• Can cause electrical failure in
jet engines

31. Pyroclastic Flows
(Nueé Ardant)
• Swift, destructive cloud of hot ash and
gases that flows rapidly downhill and
burns all in its path
– Ash weighs down the gases, which would
otherwise rise into the atmosphere
– Nueé Ardant—French for “glowing avalanche”
• Mont Pelée in Martinique
Mt. Mayon, Island of
Luzon, Phillipeans,
1984

32. Mt. Pelée, Island of Martinique, CaribbeanMt. Pelée, Island of Martinique, Caribbean
May 8,1902—The town of St. Pierre was obliteratedMay 8,1902—The town of St. Pierre was obliterated
by a nuée ardante; over 28,000 lost their livesby a nuée ardante; over 28,000 lost their lives
St. Pierre today….

33. Mt. Pelée, Island of Martinique, CaribbeanMt. Pelée, Island of Martinique, Caribbean
May 8,1902—The town of St. Pierre was obliteratedMay 8,1902—The town of St. Pierre was obliterated
by a nuée ardante; over 28,000 lost their livesby a nuée ardante; over 28,000 lost their lives
St. Pierre today….

34. 3434
Pyroclastic FlowPyroclastic Flow
From Mount St. Helens:
• Within a few hours of
the lateral blast, hot
mixtures of volcanic
gas, pumice, and ash
swept down the north
flank of the volcano at
speeds up to 100
miles an hour and
temperatures of over
1200ºF

35. 3535
Soufriere Hills Pyroclastic FlowSoufriere Hills Pyroclastic Flow
The Soufrière Hills Volcano,
Montserrat, West Indies,
began erupting on July 18,
1995.

36. 3636
Soufriere Hills Pyroclastic FlowSoufriere Hills Pyroclastic Flow

37. 3737
Lava FlowsLava Flows
• Can travel long
distances, burning and
burying everything
• Lava does not need to
actually touch an object
to set it on fire

38. 3838
Volcanic GasesVolcanic Gases
• Volcanic gases, some of which are colorless and
odorless like CO2, can cause suffocation, killing
plants, animals, and humans alike

39. 3939
Volcanic GasesVolcanic Gases

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Volcanic GasesVolcanic Gases
• Such an incident happened at Mammoth
Mountain in early 2006, where CO2
emanating from faults at the edge of Long
Valley Caldera killed one member of the
local ski patrol

41. 4141
Volcanic GasesVolcanic Gases
• Ash and gases (such as SO2—sulfur dioxide) can mix
with cloud droplets near the ground to form “vog” (a
volcanic fog that causes health problems)
• Hydrogen from lava combines with chlorine in sea water
to form hydrochloric acid, which becomes airborne as
steam, forming corrosive lava haze, or “laze”
Hawaiian vog

42. 4242

43. 4343
Structures Associated WithStructures Associated With
Intrusive VolcanismIntrusive Volcanism
• Pluton--a massive body of intrusive igneous
rock which solidifies deeply within the crust
• Batholith
• Laccolith
• Stock
• Dike
• Sill
• Vein

44. Intrusive Igneous Structures
and Their Formation

45. 4545
Structures Associated WithStructures Associated With
Intrusive VolcanismIntrusive Volcanism
• Batholith— >40 mi2
(100 km2
) in diameter, amorphous,
forms deep in the crust
– granite often forms batholiths
• Sierra Nevada Mountains
• Stock—A few mi2
in diameter, amorphous, forms deep in
the crust, may be an offshoot of a batholith
• Laccolith—Similar to a stock, but intrudes just beneath
the surface, warping surface rocks and forming a hill;
may form the base of small mountain chains
– The Black Hills, South Dakota
– Devil’s Tower, WY

46. 4646
Batholiths inBatholiths in
Western North AmericaWestern North America

47. 4747
Laccolith:Laccolith:
Devil’s Tower, WYDevil’s Tower, WY

48. 4848
DikeDike

49. 4949
SillSill
Salisbury Craig,
Edinburgh, Scotland

50. 5050
SillSill
The Purcell Sill, Glacier National Park, MT

51. 5151
VeinsVeins