Styles of Eruptions and Volcanic Hazards

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

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

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

Eruptive styles are Classified by level of eruption explosiveness

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

Columbia Plateau More than 420,000 cubic km of lava

Flood basalts

II. Hawaiian-type eruptions

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

Hawaiian-type eruptions Build shield volcanoes

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

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

More explosive eruptions Build composite cones

Mt. Shasta, California ‘A’a flows

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

Arenal Volcano, Costa Rica

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

Mt. Pelé eruption Almost 30,000 people were killed instantly Almost 30,000 people were killed instantly

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

Pyroclastic flows formed during 1968 eruption of Mt. Mayon Ash cloud is 30,000 ft high Flows caused by ash cloud collapse or lava dome collapse

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

Plinian Eruption Mt. St. Helens is good example beforeduring

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

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

Other Recent Eruptions Pinatubo = Vulcanian-type eruption 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 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

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

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

Volcanic Hazards 1. Lava Flows

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

Falling tephra in Yakima, Washington during Mt. St. Helens eruption

More Volcanic Hazards Pyroclastic flows Pyroclastic flows Mudflows - Lahars Mudflows - Lahars Toxic volcanic gases Toxic volcanic gases

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

Lava Flow Hazard Zone Map of Hawaii Historic Eruptions Mauna Loa: 33 flows since reached ocean in Kona Hualalai: 3 flows since ~ reached ocean in Kona

High effusion rates: 3-12 x 10 6 m 3 day -1 < 24 hours Steep slopes > 6 %: Hualalai: >50 % Mauna Loa: 35 % Kilauea: <5 % Fast transit times:

Lava Flows From Hualalai and Mauna Loa That Have Affected Kailua-Kona 1877

Hualalai’s last eruptions (c ) Subdivision Airport Resorts

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

Typical Mauna Loa Eruptions: Summit followed by fissure eruptions

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

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

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

LAHAR - ASH MUD FLOW

Volcanic gases Very dangerous Very dangerous CO 2, CO, SO 2, H 2 S, HCl and HF CO 2, CO, SO 2, H 2 S, HCl and HF

Hawaiian volcanoes Do not usually emit enough gas to harm people Do not usually emit enough gas to harm people Except for Vog which forms as volcano erupts and as lava enters the ocean (Even reaches O`ahu with Kona wind) Except for Vog which forms as volcano erupts and as lava enters the ocean (Even reaches O`ahu with Kona wind)

Attempts to control flows In the past, people have tried to control, direct lava flows by: In the past, people have tried to control, direct lava flows by: Diverting the flow with barriers built with bulldozers Diverting the flow with barriers built with bulldozers Diverting by bombing one or all of the following locations - the vent, edge of a flow, tube entrance Diverting by bombing one or all of the following locations - the vent, edge of a flow, tube entrance Water the flow front - not very successful! Water the flow front - not very successful!

Avoiding volcanic hazards Predict them Predict them Volcanologists getting good at predicting eruptions of dangerous volcanoes Volcanologists getting good at predicting eruptions of dangerous volcanoes Mt. St. Helens, Unzen and Pinatubo Mt. St. Helens, Unzen and Pinatubo But, missed 1993 Mayon eruption But, missed 1993 Mayon eruption

Predictions eruptions Mostly made based on monitoring: Mostly made based on monitoring: Seismic activity increases Seismic activity increases Ground tilting Ground tilting Increased heat flow Increased heat flow Increase in %sulfur in volcanic gas Increase in %sulfur in volcanic gas Because magma is moving into shallow levels under volcano! Because magma is moving into shallow levels under volcano!

Cyclic nature of Kilauea eruptions

Wai`anae Volcano Ko`olau Volcano

Thurston Lava Tube

Meteorites have struck the Earth in the past. Many meteorites are made of iron and nickel. We think this represents material of planets similar to Earth. Earth’s interior (core) is probably also composed of iron and nickel.

The end!