ISNS 4359
EARTHQUAKES AND VOLCANOES
Spring 2005
Steve Bergman, Instructor
Lecture 18. Historic Eruptions II. Krakatau 1883, Unzen 1991, Pinatubo 1991
1883 Krakatau, Indonesia [the loudest documented explosion as noted in Guinness Book of World Records]
{variably meaning- crab and to split}
1. Location: 105.5E, 6.1S, elevation: 813 m, Sunda Straits between Java and Sumatra.
2. Size & Type of volcanic feature: 7 km diameter volcanic field caldera comprising three adjoining pre-1883
cones: Rakata, Danan, & Perbuwatan (SW-NE on Karakatau Island).
3. Relationship to Plate Boundaries/ Names of relevant plates: Subduction of N-dipping Indian-Australian
plate oceanic lithosphere beneath Eurasian Plate continental lithosphere at a kink in the subduction zone.
4. Date and duration of eruption: 20 May-26-27 Aug 1883.
5. Type of Eruption/Deposits/Magma Composition: Andesitic to dacitic plinian and peleean eruptions
producing pyroclastic surge, flow, and fall deposits. The plinian ash cloud reached 40 km into the atmosphere, circled the globe
for several years, and formed >30 m thick pumice deposits within a 15 km radius.
6. Volume of erupted products: The eruption vented ~20 km3 of dacite pumice (VEI=6).
7. Area impacted by the eruption: Regions within an 80 km radius experienced total darkness for 57 hrs, within 200 km,
for 22 hrs; coastal regions within 100 km were severely damaged by tsunami; pyroclastic flows destroyed villages >40 km across
the Sunda Straits.
8. Summary of volcanic events preceding the particular event: Volcanism originated at Krakatau >10 Ma. The
416 AD caldera collapse destroyed the volcano and formed an 8 km wide, 300 m deep caldera, and left the remnant islands
Krakatau, Verlaten, and Lang. Following 200 years of quiescence (1680-1), moderate Vesuvian eruptions from ~12 vents
occurred from May to Aug 1883. Then at 2PM on 26 Aug 1883, Plinian eruptions (>30 km high) and caldera collapse (270 m
deep) produced the loudest recorded explosion on Earth (as far as 4,653 km away in Rodriguez Island, Indian Ocean; heard over
12% of the Earth’s surface) and destroyed >66% of the island. The pressure wave radiated around the world at 1200 km/hr
(detected by many weather stations) and bounced back when it met its antipode in Colombia 4 times.
9. Number of Deaths/Type of hazards: Over 4,500 people were killed by pyroclastic surges, flows, and falls as far as
40-80 km from the vent. Tsunami >40 m tall thundered onto the shores of the Sunda Strait within 30 min. and destroyed 300
villages (>1-2 km inland), killing >36,000 people (mostly in Sumatra); the tsunamis were detected in Hawaii, San Francisco, S.
Africa & England.
10. Subsequent activity: Since 1927, small frequent eruptions have constructed a 200 m tall new island, Anak Krakatau
(Child of Krakatau), with a dozen major eruptions from 1959 to 1995, most lasting less than a year. Steaming, fumarole activity,
and lava flows occurred in 1996 & 97, followed by ash eruptions in 1999-2001.
11. Notable Items: Highly charged ash particles produced lightning and St. Elmo’s fire, lighting up metallic surfaces.
Volcanic aerosols traveled westward and completed worldwide trips on 9 Sept and 22 Sept. The ash and gases injected in the
atmosphere caused 1C cooling in northern latitudes and 0.6C in mid-latitudes. Atmospheric ash initially produced blue moons
& suns, green moons & suns, followed by a pinkish halo around the sun, termed "Bishop's ring" for 3 years. Frost rings were
also produced the following winter on trees around the world. The islands were totally sterilized with isolated ecosystems.
Selected References:
Carey, S; et al., 1996. Pyroclastic flows and surges over water; an example from the 1883 Krakatau eruption. Bull.
Volcanology, 57, 7, 493-511.
Self, S., & M.R. Rampino, 1981. The 1883 eruption of Krakatau. Nature, 294, 699-706.
Simkin, T, & R.S. Fiske, 1983. Krakatau 1883-The volcanic eruption and its effects, Smithsonian Inst. Press.
Sastrapradja, Didin (ed) 1983. Proceedings of the symposium on 100 years development of Krakatau and its
surroundings, 39 papers, 476 pp.
Thornton, I. 1996. Krakatau, The destruction and reassembly of an Island ecosystem. Harvard Univ. Press
Willumsen, P. 1997. Krakatau-events and geology, a practical guide to Krakatau and surroundings, Indonesian Petrol.
Assoc., Jakarta.
8 papers in Krakatau; a century of change, GeoJournal, vol.28, no.2, pp.83-304, Oct 1992
Wohletz, K. (2000) Were the Dark Ages Triggered by Volcano-Related Climate Changes in the 6th Century?
http://www.ees1.lanl.gov/Wohletz/Krakatau.htm (suggests a proto-Krakatau eruption may have done it)
1991 Pinatubo, Philippines {the disaster averted: 5,000-50,000 lives saved} [meaning-to grow]
1. Location: 15.13N, 120.35E, elevation: 1600 m, on the island of Luzon.
2. Size & Type of volcanic feature: Ancestral Pinatubo (>40,000 yrs) was a 15 km diam. andesite-dacite
stratovolcano showing no evidence of large explosive eruptions. It may have risen as high as 2300 m above sea level
at one time. Remains of a 3.5 by 4.5 km wide caldera from the old Pinatubo are preserved. The modern Pinatubo is a
stratovolcano/dome complex, surrounded by pyroclastic flow and lahar deposits from large explosive eruptions.
3. Relationship to Plate Boundaries/ Names of relevant plates: Youngest volcano of the W. Luzon volcanic
arc, caused by eastward subduction of South China Sea oceanic lithosphere of the Eurasian Plate beneath oceanic
lithosphere of the Philippine Sea plate.
4. Date and duration of eruption: 2 Apr-12-16 Jun 1991 4 Sep 1991. A lava dome formed Jul-Oct 1992.
5. Type of Eruption/Deposits/Magma Composition: Dacite plinian and pelean eruptions producing
pyroclastic surge, flow and fall deposits. This eruption distributed over 100 m of pyroclastic flow deposits on all
sides of the volcano. The magnitudes of eruptions since that event have decreased with time. When gas and crystal
rich magma evolves in a shallow magma chamber, explosive eruptions occur, although basaltic magma mixing with
the dacitic magma in the chamber has also caused these eruptions.
6. Volume of erupted products: The upper ~150 m of the volcano was blasted away by this eruption, forming a
2.5 km diameter caldera; >5 km3 of dacite ash were erupted 15-40 km high, pyroclastic flows traveled <12-16 km,
and impacted >400 km2 of land. In all, >10 km3 of volcanic material was erupted; VEI=6). Over 17 megatons of SO2
were injected into the atmosphere.
7. Area impacted by the eruption: Pyroclastic flows covered 400 km2 and surged ~16 km from the vent. Lahars
devastated >200 km2 river valleys; Ash ~5 cm thick was deposited over a 4,000 km2 area.
8. Summary of volcanic events preceding the particular event: Six large eruptions have occurred in the last
40,000 years. Pinatubo has repeatedly experienced a relatively short explosive eruption, followed by a period of slow
growth through extrusion of lava domes. Then the volcano becomes dormant for a longer period, and much of the
material deposited during the last eruption is eroded. Finally, another explosive eruption will occur and destroy
what's left of the growth from the last eruptive period. This process seems to have repeated itself over time, creating a
somewhat stable size for the volcano. A M7.8 earthquake 16 July 1990 ~100 km N of Pinatubo may have allowed
magma movement. Tremors and rumbling was reported in August, followed by a lull until March 1991. USGS
Monitoring and evacuations began in April.
9. Number of Deaths/Type of hazards: A total of 502 people died due to primary volcanic processes and lahars (which
traveled up to 40 km) and 700 due to post-eruption famine as a result of the 1991 eruption. Over 50,000 people were displaced;
8,000 homes were destroyed and 75,000 severely damaged. Sixteen commercial jets ingested ash in their turbines, temporary
loosing them in-flight (causing >$100 million damages). Total losses >$1.6 billion; >$1 billion in damages to crops, buildings,
and property. Over 500,000 people lived within striking distance of the volcano; 58,000 were evacuated from within 30 km of the
peak.
10. Subsequent activity: Pinatubo has been relatively quiet since the 1991-1992 eruption, but it is still active. Sadly,
subsequent mudflows (from 1993-1996, totalling ~2 km3) have destroyed hundreds of villages that were re-inhabited following
the 1991 eruption.
11. Notable Items: The eruption was accompanied by the arrival of Typhoon Yunya (passing 100 km to the north),
complicating evacuation preparations, and increasing lahar hazards. The 1991 Pinatubo eruption volume is second of
the 20th century, behind 1912 Katmai AK. The volcanic aerosols spread around the earth within 3 weeks (between
30N and 10S), and covered the entire globe within 12 months. SO2 lowered global T by 0.4C and increased the
ozone hole for 1-2 years. Two global cooling effects: Aerosols reflected solar radiation, but scattering increased diffuse
radiation, enhancing photosynthesis in deciduous forests, decreasing atmospheric CO 2, & decreasing global warming.
The $1.5 million costs of the volcano monitoring saved >5,000 lives and >$250 million in potential damages.
Selected References
Newhall, C.G. and Punongbayan, Raymundo S., 1996. Fire and Mud: Eruptions and Lahars of Mount Pinatubo,
Philippines, Philippine Inst. Volcanology and Seismology, Quezon City and Univ. Washington Press, Seattle, 1126 pp.
(online at http://pubs.usgs.gov/pinatubo/)
Newhall, C.G. et al., 1997a. The cataclysmic 1991 eruption of Mount Pinatubo, Philippines. USGS Fact Sheet 0113-97.
http://wrgis.wr.usgs.gov/fact-sheet/fs115-97/
Newhall, C.G. et al., 1997b. Benefits of volcano monitoring far outweigh costs; the case of Mount Pinatubo, USGS
Fact Sheet 0115-97. http://wrgis.wr.usgs.gov/fact-sheet/fs113-97/
1991 Unzen Volcano, Japan
1. Location: 32.75N, 130.3E, elevation: 1359 m, Fugen-dake, Kyushu, Shimabara Peninsula, east of Nagasaki within
a 30-40 km E-W trending graben.
2. Size & Type of volcanic feature: ~10 km complex stratovolcano with several adjacent and overlapping lava domes.
3. Relationship to Plate Boundaries/ Names of relevant plates: Westward subduction of Philippine Sea plate
oceanic lithosphere beneath Eurasian Plate continental lithosphere, ~100 km behind the main volcanic arc in an E-W rift.
4. Date and duration of eruption: 17 Nov 1990 - 3 Jun 1991 - Feb 1995.
5. Type of Eruption/Deposits/Magma Composition: Dacite (66 wt% SiO2) lava dome collapse, pyroclastic
surges, flow and fall deposits.
6. Volume of erupted products: Only 0.01 km3 were ejected in the June 1991 eruptions (VEI=1). During
1991-1994, total amount of lava erupted reached ~ 0.2 km3, producing a dome 1.0 x 1.2 x 0.3 km tall; ~10,000 pyroclastic flows
were seismically recorded. Landslides also generated large pyroclastic flows that traveled as far as 5.5 km from the dome.
7. Area impacted by the eruption: ~<10 km2 were damaged by pyroclastic flows and <200 km2 were covered by
pyroclastic falls.
8. Summary of volcanic events preceding the particular event: Volcanic activity at Unzen began ~0.5 Ma. In
1792, collapse of the Mayu-yama lava dome created an avalanche and tsunami that killed an estimated 15,000 people, most by
tsunami. After the 1792 eruption, Unzen was dormant for 198 years. The 1990 eruption was preceded by a swarm of earthquakes
that began on 17 Nov 1989. The earthquakes gradually migrated towards the summit of Unzen over time. A phreatic eruption on
17 Nov 1990, marked the onset of the most recent eruption of Unzen. Beginning in late Jan 1991 continuous tremors were
detected beneath the volcano. The eruption resumed on 12 Feb 1991. It became stronger with time and the composition of the ash
particles indicated that fresh magma was being erupted. A volcanic dome made of dacite lava began to grow on 20 May 1991,
after ascending for 10 months at ~13 m/day from ~4 km depths.
9. Number of Deaths/Type of hazards: On 3 June 1991, one of the pyroclastic flows moved ~4 km, killing 44 people,
including volcanologists Maurice and Katia Krafft and Harry Glicken. More than 2,000 buildings in and around the town of
Kamikoba were destroyed by ~7,000 pyroclastic- and debris-flows by the summer of 1993. Debris flow frequently occurred
during the rainy season. ~12,000 people were evacuated in the summer of 1991. The number of evacuees was reduced to 3,000
by the end of 1993.
10. Subsequent activity: The dome continued to grow for 4 more years. During this time pyroclastic flows were frequently
generated by the collapses of lava blocks from margins of the dome. Generation of pyroclastic flows and major deformation of
the dome had stopped in Feb 1995. In mid-Feb 1996, Unzen generated several small block-and-ash flows. These flows were
caused by collapse of part of the volcanic dome. The flows traveled ~1 km from their source.
11. Notable Items
Cooling of the lava dome or seasonal temperature changes may have triggered the collapses. Mt. Fugen, is only 6 km
from the center of the Shimabara City (population 45,000). An active drilling campaign is currently attempting to
constrain the volcano history and penetrate magmatic conduits beneath the volcano.
Selected References
Nakada, S. et al., (eds.), 1999. Unzen eruption: Magma ascent and dome growth. Journal of Volcanology and
Geothermal Research, 89, 1-4, 315 pp. (20 papers).
UNZEN - DECADE VOLCANO home page (http://hakone.eri.u-tokyo.ac.jp/unzen/index.html)
Figure from Unzen Scientific Drilling Project: http://hakone.eri.u-tokyo.ac.jp/vrc/usdp/index.html