1. Other volcanic features
Flood basalts
Largest volcanic events in terms of volume
Volatiles, viscosity are low, so not very explosive
Cover large areas w/ thick layers of lava
Lava domes
Hardened dome/plug of magma cools quickly
Can form in hours, continue for years, decades

2. Flood Basalts

3. Lava Dome, Mt. St. Helens
Lava Domes

4. Volcanic Hazards

5. Outline
Types of volcanic hazards

6. Volcano Classification
Active: currently erupting or has erupted in historical time
Dormant: presently inactive but may erupt again (examples: Cascades)
Extinct: not active, not expected to be active for long time in future

7. Cumulative Deaths Due to Volcanic Hazards in past 2000 years

8. Causes of Deaths

9. How bad can it be? 1815 Indonesia 92,000 died*
1822 Indonesia 5,500 killed
1826 Indonesia 3,000 killed
1883 Indonesia 36,417 killed
1902 Martinique 29,025 killed
1902 Guatemala ,000 killed
1919 Indonesia 5,110 killed
1951 New Guinea 2,942 killed
1982 Mexico 1,700 killed
1985 Columbia 23,000 killed

10. Pyroclastic Flow Most deadly of all hazards
Superhot, fast moving cloud of volcanic gas, steam, debris
degrees C, 80 km/hr (hurricane speeds!)

11. Generation of pyroclastic flow
Eruption column collapse
Dome collapse
Directed blasts

12. Pyroclastic flows
Mayon, Philippines, 1984

13. Effects of Pyroclastic Flows
Destroys nearly everything in path
Structures
Burial of sites
Burn forests, crops, structures
Melt snow to form lahars

14. Building destruction
Remnant of building after eruption of El Chichon, Mexico in 1982
Note reinforcement rods bent in direction of flow

15. Effects of pyroclastic flows
Mt. St. Helens - forest destruction

16. Effects on people Physical impact Burns Inhaling superhot gases
Usually quick death

17. Examples Many examples of devastating pyroclastic flows Unzen, Japan
Chichon, Mexico
Mt. Pelee, Caribbean*

18. Mt. Pelee 1902-1903, 1929-1932 significant pyroclastic flows
Many from directed blasts, deadliest in 1902
Viscous magma filled crater
May 1902, several pyroclastic flows, traveling ~190 km/hr
Destroyed St. Pierre (~30,000 people) and other towns in area

19. Mt. Pelee
Large area affected by 1902 pyroclastic flows

20. Eruption Debris Includes cloud, bombs, ash fall
Bombs kill small # of people every year
Clouds
Planes fly into cloud - dangerous
Over 25 years, ~60 jets damaged
Ash fall
Bury cities

21. Ash fall hazards Roof collapse Mid-Afternoon - daylight gone
Water systems can clog

22. Kamchatka eruption, seen by space shuttle
Cloud Hazard
Ash from Mt. Spurr traveled around for days (satellite image)

23. Example - Mt. Vesuvius 79 AD
Cause of volcano: subduction
Region near Pompeii also had earthquakes, but city of ~20,000 people not deterred to move
Significant volume of material erupted (4 km3) in first wave
Pompeii buried by ash/pumice 3 m deep
Later pyroclastic flows continued to bury city

24. Vesuvius
Remains of Pompeii after 79 AD eruption

25. Tsunami
Wave caused by undersea vertical displacement (like earthquakes)
Volcanic eruption can also cause tsunami
Pyroclastic flow or lava dome avalanche
Collapse of cone or crater

26. Example - Krakatau 1883 Stratovolcano between Java and Sumatra
Subduction zone
Collapse led to tsunami ~35 m (115 ft)
Death toll ~36,000
New cone appeared in 1927

27. Collapse of Krakatau
Anak Krakatau

28. Lahars
Mudflow of volcanic debris, produced when pyroclastic debris or lava mix with rain, snow, ice, lakes
Can travel quickly (40 mph) and significant distances (10s of miles)

29. Dark pathways - lahars triggered by Mt. St. Helens eruption, 1985
“Cloud” upriver: lahar traveling down riverbed in Guatemala

30. Home destroyed from lahar - Mt
Home destroyed from lahar - Mt. Unzen, Japan lava dome collapse and later rains, 1993

31. Example - Nevado del Ruiz 1985
Colombian volcano, small glacier on top
Small eruption caused melting, sending mud down the mountain
Covered most of town of Armero with ~26 ft thick mud
Killed ~22,000

32. Nevado del Ruiz, 1985
River valley with lahar remains
Town of Armero

33. Famine Indirect hazard Eruptions change climate
Can harm plants, animals

34. Iceland eruption, 1783 Fissure eruption of basalt
Released gas rich in SiO2 and fluorine
Slowed grass growth and added significant amounts of fluorine to grass
Killed significant population of livestock
~20% of Iceland population died due to famine

35. Tambora, 1815
Indonesian volcano, most violent eruption in last 200 years
Significant Plinian eruption
Next pyroclastic flows (12mi3 of material)
Deaths in region ~90,000 (10% during eruption, 90% later)
year without summer
Affected global climate

36. Gas Gas can escape from basaltic magmas
CO2 gas is common
Depending on gas, can kill plants in region
Can also be trapped in water

37. Example - Lake Nyos, Cameroon
Area of failed rifts with some remaining volcanic activity
gas burp from the lake
Sent rivers of gas down into valleys ~25 km (16 mi)
Effects - ~1700 deaths, no animals alive
Plants ok though

38. Why? CO2 gas leaking out of basaltic magma
Dissolved in bottom waters of lake (held down by pressure)
Some event caused overturn
Eruption, earthquake, landslide, temp change all possible triggers
Gas release “river” ~50 m thick

39. Lake Nyos

40. Lake Nyos
Efforts to pump water, gas out of lake

41. Continued hazard? YES! Still some gas remaining Continues to build up
Possible ways to pump gas out to reduce risk

42. Lava Flows Not big hazards in terms of fatalities
Moves too slow to kill people
Can destroy towns, villages

43. Kilauea, HI
Few lives lost
Mostly structural losses

44. 1973 Flows in Iceland Lava flows threatened town, harbor
Built diverters to control flow
Sprayed water to harden flows, move to flow in other direction away from harbor

45. Man vs. volcano!

46. Actually gained land and improved harbor

47. Next Time
U.S. volcanoes and related hazards