PowerPoint Presentation - Geophysics 189 Natural Hazards

1
Volcanic Hazards in the U.S.
2
Outline

• Cascades
• Mt. St. Helens
• Mt. Rainier
• Crater Lake
• Mt. Shasta
• Lassen
• Other eruptions
• Yellowstone
• Long Valley
• Valles Caldera

3
(No Transcript)
4
Locations of U.S. Volcanoes
5
Subduction Zone Volcanoes
6
Cascades

• Subduction of Juan de Fuca plate beneath North
  America
• Water released from slab aids melting above
• Magma travels toward surface, some cools, other
  erupts
• 6-7 of these volcanoes have erupted in last 200
  years

7
Cascades
8
Mt. St. Helens

• Very active over last 4000 years
• Eruptions every century
• Date past eruptions using old deposits

9
St. Helens (pre-1980)
10
Mt. St. Helens 1980

• March small magnitude earthquakes
• Indicates magma moving
• Also northern side bulge

11
Mt. St. Helens 1980
bulge

• April 1.2 mi2 bulge rising 100 m
• Growing by 1.5 m/day

12
Mt. St. Helens 1980

• May 18th
• Magnitude 5.1 earthquake
• Triggered landside on north side

13
Mt. St. Helens 1980

• May 18th
• Lahars forming after landslide
• Snow, ice near top of mountain

Bridge destroyed by lahar
14
Mt. St. Helens 1980

• May 18th
• Lateral blast - pyroclastic flow
• Occurred after landslide removed pressure on side
  of mountain
• Destroyed area 550 km2
• Timescale minutes from earthquake

15
Mt. St. Helens 1980

• May 18th
• Vertical eruption
• Plinian eruption, reached 12 mi (20 km) high
• 1 km2 ash

16
Mt. St. Helens, post eruption

• Rebuilding
• Different shape
• Lava dome builds

17
Effects of 1980 eruption

• 62 deaths
• Significant stream/valley modification
• Clogged Columbia River, shipping channels
• Forest destruction

18
Mt. St. Helens Figs
19
Current Activity, Mt. St. Helens

• Sept. 23, 2004 - volcano started grumbling again
• Earthquakes, uplifted crater floor, some steam
  eruptions 9 days later

20
Current Activity, Mt. St. Helens

• Growth of new lava dome

21
Current Activity, Mt. St. Helens
New dome growth indicates magma moving to
surface, producing steam Oct 2004
Steam plume, Jan3 2005
22
(No Transcript)
23
Cascades
24
Mt. Rainier

• Classified as most dangerous volcano in U.S.
• Large glacier system
• Frequent earthquakes
• Active springs
• Just outside Seattle-Tacoma

25
Why So Dangerous?

• Could have eruption/landslide like St. Helens
• Springs act to weaken structure
• Significant lahar potential

26
Previous Activity

• Mudflows date back 5,000 years
• Most recent 500 years ago
• Significant population centers on lowlands
  (100,000 people)

27
Activity
28
Cascades
29
Crater Lake

• Today popular tourist spot

30
Mt. Mazama 5677 B.C.

• Stratovolcano in Cascades
• Major eruption of lava, pyroclastic debris
• Covered much of Pacific Northwest, Canada with
  thick layer

31
Crater Formation

• Magma chamber empties, leaves void
• Top collapses

32
Crater Formation

• Magma chamber empties, leaves void
• Top collapses

33
Lake Formation

• Forms over time
• Small volcanic cone in center

34
Cascades
35
Mt. Shasta and Shastina

• 2nd and 3rd largest volcanoes in Cascades
• Last eruption in 1786, at least 3x in last 750
  years
• Development ongoing in region

36
Mt. Shasta
37
Lahar paths
38
Pyroclastic Flow Danger
Note the increasing number of towns/developments
in higher hazard zones
39
Cascades
40
Lassen Peak

• Actually lava dome forming in region of past
  large volcano
• Significant eruptions in 1914-1917
• Lava flows, pyroclastic flows, ash cloud
• Eruptions may have been helped by melting snow
  adding to groundwater system

41
Lassen
42
Outside Cascades

• Significant caldera events in
• Yellowstone
• Long Valley
• Valles

43
Yellowstone, WY

• Hotspot volcanism, makes tracks across U.S.
• Youngest volcanics at Yellowstone
• Eruptions at 2 million, 1.3 million, 600,000
  years ago
• Catastrophic eruptions! (600,000 yr event - VEI
  8)
• Active system, geysers, geothermal activity today

44
Yellowstone event 600,000 years ago

• Erupted 1,000 km3 of magma
• Mt. St. Helens 1km3 of magma
• Created caldera 75 km long, 45 km wide

45
Long Valley Caldera

• Not traditional hotspot, but active magma system
• Large eruption 760,000 years ago
• Covered 1,500 km3 with pyroclastic flow
• Activity in 1980, more next time

46
Long Valley
47
Valles Caldera

• Associated with Rio Grande Rift
• Last eruption 1 million years ago

48
Next Time

• Volcanic eruption prediction efforts