Styles of Eruptions and Volcanic Hazards

1. Styles of EruptionsandVolcanic Hazards

2. Styles of volcanic eruptions • Some volcanoes may erupt only once - monogenetic (Diamond Head) • Other volcanoes erupt many times - polygenetic (Kilauea) • Some erupt very gently (Kilauea) • Others are very violent and explosive (Mt. St. Helens, Mt. Pinatubo) • How come?

3. Explosive volcanoes found associated with subduction zones • Explosiveness is a function of magma viscosity (resistance to flow) • Magmas that generate the explosive volcanoes are much more viscous than the non-explosive magmas • More silica, cooler magma, more gas

4. Hawaiian magmas • Not very explosive • Not very viscous • Low silica, hot magma, moderate gas content

5. Eruptive styles are Classified by level of eruption explosiveness

6. I. Flood eruptions • Least explosive eruptions • Very fluid basalt erupted in very large quantities VERY FAST • Lavas erupted over large areas • Thought to develop as hot spots burn thru crust

7. Columbia Plateau More than 420,000 cubic km of lava

8. Flood basalts

10. II. Hawaiian-type eruptions

11. Hawaiian-type eruptions • The next least explosive kind of eruption • Fluid magmas with small amounts of gas • Eruptions relatively gentle • Periodically have a violent eruption but very rare - Drive in volcanoes

12. Hawaiian-type eruptions Build shield volcanoes

13. phreatoplinian Surtseyan Plinian Fragmentation (grain size) Peléan Vulcanian Strombolian Intensity (dispersal) Styles of explosive volcanism Modified from Julia Sable

14. III. Strombolian eruptions • Named for volcanic island off coast of Italy • Characterized by less fluid lavas • Moderate explosive activity • Tephra common • Lots of ash blankets country side • Basalt and andesite common • Large steep-sided composite volcanoes built by repeated Strombolian eruptions

15. More explosive eruptions Build composite cones

16. Mt. Shasta, California ‘A’a flows

17. IV. Vulcanian eruptions • Characterized by more viscous lavas • “Stubbly” flows are common • Lots of ash • Andesite most common

18. Arenal Volcano, Costa Rica

21. V. Peléan eruptions • Named for 1902 eruptions of Mount Pelée on Martinique in the Caribbean

22. Mt. Peléeruption Almost 30,000 people were killed instantly

23. Peléan eruptions • Lavas highly viscous, very explosive • Explosive eruption of highly gas-charged lava leads to nuée ardente (glowing avalanche) or pyroclastic flow which move at 60+ kph and are 300deg C inside • Don’t outrun these guys!!!

24. Pyroclastic flowsformed during 1968 eruption of Mt. Mayon Ash cloud is 30,000 fthigh Flows caused by ash cloud collapse or lava dome collapse

25. VI. Plinian Eruptionmost powerful eruption • Named for Roman naturalist killed in explosion of Mt. Vesuvius in 79 A.D • Very destructive • Accompanied by major collapse

26. Plinian Eruption Mt. St. Helens is good example before during

27. Plinian = most powerful eruption • Crater Lake in Oregon formed by similar explosive eruption • Ash from this volcano (Mt. Mazama) found all over the Pacific Northwest & as far east as the Mississippi River!

28. Plinian = most powerful eruption • Greatest Plinian eruptions of modern times: • 1813 explosion of Tambora volcano (eastern Indonesia) • 1883 explosion of Krakatau (Sunda Strait between Java and Sumatra) • Explosion heard in northern Australian, 2400 km away

29. Other Recent Eruptions • Pinatubo = Vulcanian-type eruption • Mt. Unzen (Japan,1991) -- generated a number of lava domes that collapsed, sending pyroclastic flows down the side of the volcano, so it can be classified as a Peléan eruption

30. Volcanoes & Plate Tectonics • OK. So, where do you find all these volcanic eruptive styles? • Flood eruptions - atop hot spots • Hawaiian - at hot spots & along MOR • All the rest are associated with subduction!

31. phreatoplinian Surtseyan Plinian Fragmentation (grain size) Peléan Vulcanian Strombolian Intensity (dispersal) Styles of explosive volcanismWhat are the hazards?

32. Volcanic Hazards 1. Lava Flows

34. Volcanic Hazards 2. Falling Tephra Like one sees at the beginning of the movie Dante’s Peak.

35. Falling tephra in Yakima, Washingtonduring Mt. St. Helens eruption

36. More Volcanic Hazards • Pyroclastic flows • Mudflows - Lahars • Toxic volcanic gases

37. Hazards in Hawaii Lava flows Note: The next few slides are courtesy of G&G graduate student Chris Gregg

39. Lava Flow Hazard Zone Map of Hawaii Historic Eruptions Mauna Loa: 33 flows since 1843 5 reached ocean in Kona Hualalai: 3 flows since ~1800 2 reached ocean in Kona

40. High effusion rates: 3-12 x 106 m3 day -1 Steep slopes > 6 %: Hualalai: >50 % Mauna Loa: 35 % Kilauea: <5 % < 24 hours Fast transit times:

41. Lava FlowsFrom Hualalai and Mauna Loa That Have Affected Kailua-Kona 1877

42. Hualalai’s last eruptions (c. 1800-1801) Resorts Airport Subdivision

43. MAUNA LOA’s Radial Vents (33) and Rift Zones Historic radial vent eruptions: 1843, 1859, 1877, 1935

44. Typical Mauna Loa Eruptions: Summit followed by fissure eruptions

45. What Controls the Flow Paths of Lava Flows?TopographyWhat Controls the Speed of Lava Flows?Slope angle, surface roughness, eruption rate, lava type (viscosity)

47. 1950Eruption: Flow velocities 16-48 km/hr Note that all of these hazards are associated with the big island! How come?

48. Worst volcanic hazards often occur after major eruptions • Ash covers sides of volcano • Ash becomes unstable during heavy rain • Ash mud flow - LAHARS • 10 years+ after Pinatubo eruption, mudflows were still killing people

49. LAHAR - ASH MUD FLOW LAHAR - ASH MUD FLOW LAHAR - ASH MUD FLOW