Four Classic EruptionsEthan and Corbin

Vesuvius, AD 79

Background● 5 February AD 62: Earthquake near Naples

○ Small towns like Herculaneum, Pompeii effected

■ Residents unconcerned

○ We now know major eruptions preceded by seismic activity.

● Vesuvius had long been inactive

● People used it’s fertile soils to cultivate

● Intermittent Earthquakes continued for next 16 years

○ Little attention paid to them

Pliny’s Account● Gaius Pliny (“Pliny the Elder”)

○ Famous naturalist, admiral

○ Died during eruption

● Tacitus

○ Historian

○ Asked Pliny’s nephew, “Pliny the Younger”, for account of events

■ Pliny the Younger had survived the eruption, 17 y/o

● Best eyewitness account of the events

Events● 1 PM on August 24, AD 79, large cloud appeared

● Grew rapidly, rising thousands of meters

○ Looked like a “Mediterranean pine tree”

○ Hot ash and sizable lumps of pumice showered around Volcano

● At Nightfall, fires started by falling hot pyroclasts

○ Lit up ash cloud with a red glare

● Next morning

○ Earthquakes/tremors

○ Sun obscured by Cloud, causing darkness

○ Electricity built up in cloud causing Flickers

○ Tsunamis generated by Earthquakes

Cont.● Pliny and his mother had escaped via chariot to outside of town

● They were engulfed in darkness for a long time until sun slowly emerged

● Immense Damage

○ Vesuvius now looked like stump

○ No movement/town in sight

○ Carpet of grey ash covered everything

○ Thousands dead

Pompeii & HerculaneumPompeii:

● 9 km downwind, buried in 3m of Tephra (“Plinian eruptions”)

● Rendered uninhabitable

○ ~20,000 inhabitants pre-eruption

○ Death toll uncertain

● Ravaged during the Renaissance

○ In search of valuables

○ Archaeologists later observed many things preserved under pumice

■ People killed suddenly by searing hot dust and gas

● Pyroclastic Surges

○ Ground hugging dust cloud surges

Pompeii & HerculaneumHerculaneum:

● Southwest flank of Volcano, just as close as Pompeii

○ Was overwhelmed in a matter of minutes by flows and surges

○ Buried more than 20 meters deep

● Dusty ash and pumice compacted

○ Presence of new town above ruins

○ Extremely difficult to excavate

● ~40,000 sq. meters excavated; some tunneling done

○ Still very much unknown

● Hundreds of Skeletons by shore

○ People killed seeking refuge in arched chamber by beach

KrakatauKrakatau is a island and volcano located

in the Sundra Strait, a major early trading

route. It is situated in Indonesia, between

the islands of Sumatra and Java. Seismic

activity has always happened around

Krakatau and the surrounding islands

● The island was very rarely visited before 1883

○ Loggers and Ships utilized the resources on the island

● September 1, 1880 an earthquake in the area destroyed a Javian lighthouse and

was felt as far away as Australia

● On May 20, 1883, three years after the first major recorded earthquake, Krakatau

visibly became alive

○ Audible booms heard from 150 kilometers away

○ Huge pressure waves emanated throughout the local area

● One week later, a group of scientists set foot on the island to take samples and

observe, and it was the last time anyone saw the island until after the explosion

○ Took surface samples and observed three different steam columns

● The island continued to be active, and people

became acclimated to the noise

● On June 9, 1883, locals reported seeing a second

eruption column coming from the island

○ Vegetation was destroyed

○ Krakatau shown to be very active

● A Dutch surveyor sailed around the island,

collecting samples and observed that there were

now three eruption columns and multiple small

steam columns rising

● This was on of the last observations recorded

before the eruption

Eruption Column

● So few local survivors, some of the

details are not exact about the eruption.

● In a 150 km radius from Krakatau, very

loud explosions could be heard in ten

minute intervals

● Black clouds rose to 25 km over

Krakatau, and explosions were starting

to be heard from 250 km away, about

the distance from Stanford to Fresno

● Electrical discharges were starting to be

seen in the rising plume

● Passing ships began to experience St. Elmo’s Fire, a

phenomenon where the atmosphere is highly

electrically charged that the tips of the mast began

to glow purple.

● At approx. 4 A.M on August 27, 1883, three loud

explosions reverberated throughout the world

● The third, by far the loudest, broke pressure gauges

50 km away and was mistaken as a gunshot from

3647 km away.

● Tsunamis ravaged the shores of many coastal towns, killing

around 36,000 and completely destroying all traces of some

towns.

○ Building were swept away; docks were destroyed; villages were leveled

● The island of Krakatau was now around ⅓ the size, with a

massive caldera formed below sea level and filling in with

water

● The tephra emitted by the explosion formed sandbanks on

the other surrounding islands, making them considerably

larger.

● Hot gas was spewed 40 km away, where it swept through

and burnt people

● This was one of the largest recorded explosions

Mt. Pelée, 1902

Background● St. Pierre

○ principal town on Martinique(small Island in Caribbean)

○ Prosperous French colony

○ Pop. about 20,000

● Mt. Pelée

○ 1400 m high, surrounded by clouds

○ Both town and mountain hailed for natural beauty

● Previous eruption in 1851

○ Many residents had witnessed

○ Fumaroles began increasing in time leading up to eruption

Background● 27 April, 1902

○ Small showers of ash, strong sulphurous fumes

○ By May 4th, loud explosions frequently occured

■ Streets covered by substantial amount of ash

● 5 May, 1902

○ First lethal blow

○ Water ponded in “Etang sec” burst out of crater walls

■ Boiling hot

■ 90 km an hour down the mountain

■ 23 workmen died at rum distillery; caused tsunami as well

● May 11 election scheduled

○ Authorities didn’t want interference

○ No evacuation issued; “scientists” said no reason to fear

○ 28,000 in the town by May 8

Eruption● May 8, 1902, 7:52 AM

○ Telegraph traffic halts

○ Big clock found frozen

● Detonations heard, black cloud rolled down slopes of Mt. Pelée

○ Spread into fan which engulfed St. Pierre

○ Set town completely on fire

● “Nuées ardentes” glowing clouds

○ One of most lethal mechanisms of erupting volcano

○ Gravity-driven pyroclastic flow

■ Dense part hugs ground, the rest towers 2 to 3 km high

○ Hot gas and incandescent solid particles

○ Thousands of rum casks burst open, lit on fire, and ran through the town

Aftermath● Everybody in St. Pierre(~30,000) perished, except a mere couple

○ Either by of force of blast, or searing heat

○ Initial blast only lasted a few moments

● ‘Prisoner of St. Pierre’, Augustus Ciparis

○ Incarcerated in town jail at time of blast

○ Extremely secure cell; only opening was tiny grating above door

○ Remained alone in cell til 4 days after eruption

■ Islanders heard his cries for help

■ He had severely burned back and legs

■ Survived on bowl of water in cell

○ Provided important account of his experience

● More nuée’s throughout the year, one deadly in Morne Rouge

● In November, giant spine of solid lava rose from crater(310 m high)

Mt. Saint Helens ● Mt. Saint Helens is located in southern Washington

state.

● It is one of the best documented volcano eruptions and

was one of the last major eruptions in the United

States.

● The volcano was suspected to be be close to erupting

due to the fact that it had some of the most recent

seismic activity in the continental United States.

● On March 21, 1980, a magnitude 4.2 earthquake shook

the earth surrounding St. Helens, and evacuation plans

began immediately.

● The outer edges of the volcano began to “balloon”,

expanding about 1 m a day.

Mt. Saint HelensOn May 18, 1980, an ascending tower of magma shook the surrounding area, causing a

magnitude 5 earthquake, which then set off the chain events of the explosion

● This caused for both mudslide and volcano side effects

● A mixture of rock, ice, and soil plummeted down the northern face of the volcano,

having so much energy that it climbed 100 meters up another slope, and fell down

in the valley under St. Helens.

○ The mudslide is predicted to have moved 75 m a second, around 175 miles an hour

● Mudflows caused the most extensive amount of damage, destroying highways,

bridges, houses, and infrastructure.

Mt. Saint Helens● As the north side of the mountain

began to fell, a blast of hot gases started

to travel.

○ This blast was initially behind the mudslide,

but soon overtook and began to burn large

swathes of forest.

● There were around 60 fatalities caused

by the blast

● The blast in mudslide happened in the

first few minutes, and afterwards, fresh

magma from Earth’s mantle began to

ooze, forming a high vertical eruption

column.

● The vertical column was solid particles suspended in hot gas,

called pumice flows

● Pumice accumulated to over 40 meters deep, and allowed

scientists to walk over them without any repercussions, even

though two meters below the surface the temperature was 300

celsius

● The mudslide destroyed trees in its path, while also being hot

enough to leave large piles of charcoal over the valley floor.

● The dark cloud formed by the ash spread over some Western

United States, and affecting farms and vehicles.

● Mt. Saint Helens was one of the worst observed volcano

eruptions in the continental United States and shows how study

of volcanoes can save hundreds of lives