Four Classic Eruptions

• Thera/Santorini - 1,620 BC– Impact on Minoan Civilization; legend of Atlantis

• Vesuvius - 79 AD– Detailed eyewitness accounts; well excavated ruins

• Krakatau - 1883– First instrumental data during major eruption

• Mt. Pelée - 1902– >30,000 people killed in a single dome collapse event

that generated dense block and ash flows

Volcanic Explosivity Index

VEI Description Plume HeightVolume Classification How often Example0 non-explosive <100 m 1000s m3 Hawaiian daily Kilauea1 gentle 100-1000 m 10,000s m3 Haw/Strombolian daily Stromboli2 explosive 1-5 km 1,000,000s m3 Strom/Vulcanian weekly Galeras, 19923 severe 3-15 km 10,000,000s m3 Vulcanian yearly Ruiz, 19854 cataclysmic 10-25 km 100,000,000s m3 Vulcanian/Plinian 10's of years Galunggung, 19825 paroxysmal >25 km 1 km3 Plinian 100's of years St. Helens, 19816 colossal >25 km 10s km3 Plin/Ultra-Plinian 100's of years Krakatau, 18837 super-colossal >25 km 100s km3 Ultra-Plinian 1000's of years Tambora, 18158 mega-colossal >25 km 1,000s km3 Ultra-Plinian 10,000's of years Yellowstone, 2 Ma

Volcano Country Date VEI Volcano TypeVesuvius Italy 5960 BC 5 ComplexVesuvius Italy 3580 BC 5 ComplexVesuvius Italy 79 AD 6 ComplexEtna Italy 1500 BC 5? ShieldSantorini Greece 1650 BC 6 Shield

Eruption magnitude can either be measured based on the volume of lava ejected as tephra (ash and pumice) during an explosive eruption or the volume of lava extruded during an effusive eruption. VEI is a log scale and is empirically derived from historical data.

VEI Redux

Source: USGS

NB: Volumes areDRE (dense rock equivalent)

Deadliest Eruptions Since 1500 AD

Eruption Year Casualties Major CauseNevado del Ruiz, Colombia 1985 25,000 MudflowsMont Pelée, Martinique 1902 30,000 (29,025) Pyroclastic flowsKrakatau, Indonesia 1883 36,000 (36,417) TsunamiTambora, Indonesia 1815 92,000 StarvationUnzen, Japan 1792 15,000 (14,030) Volcano collapse, TsunamiLakagigar (Laki), Iceland 1783 9,000 (9,350) StarvationKelut, Indonesia 1586 10,000  

Hellenic Arc - Regional Tectonic Setting

NASA Space Shuttle ImageNovember 13, 1995.

Eruption Frequency vs. VEIN

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Similar frequency-magnitudebehavior as observed forearthquakes.

Volcanic Deaths by Country

Source: O. Melnik, Bristol

1600-1982

Total = 238,000

Location Map: Thera/Santorini, Greece

Steep cliff facesdefine ancientcaldera wall

NASA 1983 Shuttle Image

Santorini Stratigraphy

Photos: R. Decker

Minoan Tephra - 1,650 BC

Basalts and Andesites

Caldera Wall - formedduring 21 ka event

50 m deposit of Minoan Tephra

Kameni Islands

Photo: R. Decker

Islands for after the caldera forming event that deposited the Minoan Tephra in 1,620 BC. Eleven lava flow eruptions since 197 BC, with most recent being in 1950 on Nea Kameni.

Thera Summary• Thera was an important center of Minoan civilization.

Eruption has been linked to Atlantis legend.

• Plinian eruption and caldera collapse event at 1,620 BC. Contributed to the decline and ultimate demise of Minoan culture ~1,450 BC.

• ~20 km3 of tephra was deposited in the sea and on adjacent islands

• Large tsunamis were generated during the eruption, which affected coastal Mediterranean cities.

• City of Akroteri was buried in 1-2 m of ash, but the population of ~30,000 was apparently evacuated prior to the eruption as no bodies were found during excavations.

Vesuvius, Italy

Photo: C. Wood and NASA (above)

Primary Plinian & Sub-Plinian Eruptions of Somma-Vesuvius

Name of the Eruption Age (years before present or AD)

Codola 25000

Basal Pumices ( Sarno)  17000

Greenish Pumices  15500

Mercato (Ottaviano)  7900

Novelle  no date available

Avellino  3750

Pompeii 1900 (79 AD)

Pollena 472 (AD)

1631 1631 (AD)

Source: http://vulcan.fis.uniroma3.it/vesuvio/vesuviustext.html

79 AD Eruption Chronology - I• Greek and Roman scholars knew that Vesuvius was a volcano

before 79 AD.• Feb. 5 AD 62, large earthquake jolted region that is now

Naples. Common for region, so they were largely ignored. Events caused significant damage to Pompeii and Oplonti. Seneca stated that quakes lasted several days and weakened with time; he advocated for future hazard planning.

• Pliny the Elder was the admiral of the roman fleet based in Misenum; he went to rescue people close the volcano and died (probably of a heart attack) once on shore near Stabiae (downwind of the eruption).

• Pliny the Younger observed the eruption from Cape Misenum (~20 km away) and his letters form the basis of our detailed knowledge of a large explosive event and subsequent column collapse. “Plinian” eruptions are named in his honor.

The Route of Pliny the Elder

Source: http://vulcan.fis.uniroma3.it/vesuvio/79_eruption.html

79 AD Eruption Chronology - Pliny’s Account

• 1 PM on 24 August large “cloud” appeared in sky above Vesuvius. Reported to resemble a Mediterranean pine tree.

• By nightfall, pumice fragments were falling on Stabiae. Earthquakes shook the area.

• At dawn, sunlight was blocked from heavy ash fall. Sulphurous fumes were widespread. Lightning discharged within the ash cloud.

• Tsunamis were generated by the earthquakes. Similar phenomena were described for the 1631 eruption.

• Sky was completely blackened at Misenum.

• Smooth cone of Vesuvius was revealed to be a stump, once ash had finally cleared.

79 AD Eruption Destroyed Pompeii

Photo: R. Decker (right) andPompeii Museum (above)

Victim of a pyroclastic surge

View of Vesuvius from Pompeii

Pumice Deposits from Early Airfall

Victims in Later Pyroclastic Surge Unit

Indonesian Island Arc Volcanoes

Location Map, Krakatau

Photo: R. Decker

LANDSAT

Anak Krakatau - Emergent since 1927

Tsunami Inundation and Ship Tracks - 1883 Eruption

All three ships survived the eruption despite their proximity.

Atmospheric Pressure Record at Batavia Gasworks

Sound wavestook ~5 mto reach Jakarata.

Note multiplepressurepulses withlargest at 10:15 AM local time,which caused the barometerto go offscale.

First volcanicinfrasoundmeasurements!

Discreteexplosions orPFs?

Tide Gauge Record Tandjong Priok

Normal Tides

Arrival of tsunami

~2 hr wave periodsuperimposed ontides.

Pre-1883 Reconstruction

Post-1883 Reconstruction

1883 Krakatau Eruption Summary• Rakata volcano was the largest center on Krakatau Island prior to eruption.

800 m AMSL.

• Krakatau and nearby islands were uninhabited.

• Vague reports of eruptions on the islands in 1680 and 1681.

• Frequent minor earthquakes in 1870’s near Sunda Straits.

• Eruption sequence began suddenly on 20 May 1883. Audible explosions >150 km away. Ash deposited from air fall >500 km away.

• Volcano quieted down by May 27. Close approach by ship yields reports of deafening noise.

• Climatic eruption began on August 26 and continued until August 27, 1883. Several ships were in close proximity during eruption.

• Most powerful explosion occurred 10:02 AM and was heard 4811 km away at Rodriguez Island in the Indian Ocean. Pressure transient of 1.45 mbar recorded in Tokyo.

• Marine ignimbrite deposit is 40 m thick in places. ~20 km3 DRE erupted.

Lesser Antilles Island Arc and Caribbean Plate

Caribbean

seismicity: epicenters < 30 km depth from USGS

Lesse

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PRVI

Lesser Antilles Active Volcanoes

Mt. Pelée and St. Pierre in 1987

Map of Devastation of May and August PFs at Mt. Pelée

Volcano was active for weeksprior to major dome collapse.

Citizens were forced to stayin town for local election thatwas to take place on May 11.

Pelée Stratigraphy - 14,000 yBP

Distribution of Pelean Deposits

Distribution of Plinian Deposits

Mt. Pelée: Future Volcanic Hazards