Geology of the Hawaiian Islands Class 10 12 February 2004
Styles of volcanic eruptions Styles of Eruptions and Volcanic Hazards
Some
volcanoes may erupt only once (Diamond Head) Other volcanoes erupt many times (Kilauea) Some eruptions gentle (Kilauea) Others very violent and explosive (Mt. St. Helens, Mt. Pinatubo)
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Explosive volcanoes found in subduction zones Explosiveness
is a function of magma
viscosity Magmas that generate the explosive volcanoes more viscous than the nonnonexplosive magmas
Hawaiian magmas Not
very explosive Not very viscous
Eruptive styles Classified by level of eruption explosiveness
Flood eruptions Least
explosive eruptions Very fluid basalt erupted in very large quantities Lavas erupted over large areas
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Columbia Plateau More than 420,000 cubic km of lava
Hawaiian-type eruptions
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Hawaiian-type eruptions The
next least explosive kind of eruption Fluid magmas with small amounts of gas Eruptions relatively gentle
Fragmentation (grain size)
More explosive eruptions Build composite cones
Hawaiian-type eruptions Build shield volcanoes
Surtseyan
phreatoplinian
Peléan
Plinian
Vulcanian Strombolian
Intensity (dispersal)
Modified from Julia Sable
Styles of explosive volcanism
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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 steepsteep-sided composite volcanoes built by repeated Strombolian eruptions
Mt. Shasta, California
‘A’a flows
Vulcanian eruptions Characterized
by more viscous lavas “Stubbly” flows are common Lots of ash Andesite or dacite most common Arenal Volcano, Costa Rica
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Peléan eruptions Named
for 1902 eruptions of Mount Pelée on Martinique in the Caribbean
Mt. Pelé eruption Almost 30,000 people were killed instantly
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Peléan eruptions Lavas
highly viscous, very explosive Explosive eruption of highly gasgas-charged lava leads to nuée ardente (glowing avalanche)
Plinian = most powerful eruption Named
for Roman naturalist was killed in explosion of Mt. Vesuvius in 79 A.D Very destructive Accompanied by major collapse
Nuées ardentes formed during 1968 eruption of Mt. Mayon Ash cloud is 30,000 ft high
Plinian Eruption Mt. St. Helens is good example
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Plinian = most powerful eruption
Plinian = most powerful eruption Crater
Lake in Oregon formed by similar explosive eruption Ash from this volcano (Mt. Mazama) Mazama) found all over the Pacific Northwest
Greatest
Plinian eruption 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
Pinatubo
= VulcanianVulcanian-type eruption Mt. Unzen (Japan,1991) -- generated a number of lava domes that collapsed, sending Nuées ardentes down the side of the volcano, so it can be classified as a Peléan eruption
Fragmentation (grain size)
Other Recent Eruptions
Surtseyan
phreatoplinian
Peléan
Plinian
Vulcanian Strombolian
Intensity (dispersal)
Styles of explosive volcanism
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Volcanic Hazards Lava Flows
Volcanic Hazards Falling tephra
Falling tephra in Yakima, Washington during Mt. St. Helens eruption
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Volcanic Hazards Glowing
avalanches Mudflows Toxic volcanic gases
Hazards in Hawaii 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 1843 5 reached ocean in Kona Hualalai: 3 flows since ~1800 2 reached ocean in Kona
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High effusion rates: 3-12 x 106 m3 day -1 Steep slopes > 6 %: Hualalai: >50 % Mauna Loa: 35 % Kilauea:
