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Volcanic Hazards I.G.Kenyon

Eruption Victims and causes of death

1902, Mont Pelée, Martinique

29,000 (pyroclastic flows)

1902, Santa Maria, Guatemala

>2000 (ashfall); >5000 (disease)

1911, Taal, Philippines

1400 (pyroclastic flows)

1919, Kelut, Indonesia

5000 (mud flows)

1929, Santiaguito, Guatemala


1930, Merapi, Indonesia


1951, Lamington, PNG


1982, El Chichón, Mexico

>2000 (pyroclastic flows)

1985, Ruiz, Colombia

23,000 (mud flows)

1991, Pinatubo, Philippines

360 (ash fall); 140 (mud flows); 700 (disease)

Volcanic disasters in perspective:

Volcanic disasters of the 20th century

Volcanic Hazards – Summary Diagram

Primary Volcanic Hazards

Lava Flows

Pyroclastic Flows

Ash and Tephra Fall

Volcanic Gases

Lava Flows

More of a threat to property than human life

Basalt fissure eruptions are the most

dangerous reaching speeds of over 50km

per hour on steep slopes and can spread

tens of kilometres from their source

Andesitic and rhyolitic lavas move

slowly and rarely spread more

than 8km from their source

Lava Flows – Paricutin, Mexico 1943-1952

The church is one of the few buildings visible

above the andesitic lava flows which covered 25 km²

The city is located 5km away from the active vent

Remains of the city of San Juan de Parangaricutiro

Lava Flows - Hawaii

In Hawaii recent lava flows

have buried roads, housing

developments and cars.

In one place, basalt almost

completely submerged a

parked (empty) school bus

When lava at over 1000°C

comes close to a house,

the house erupts in flame.

Usually people have

time to get out of their

way but not always with

all their possessions

Lava Flows - Hawaii

Kilauea in Hawaii has been erupting since

1983, covering 78 km² and destroying

180 houses but with no deaths

The eruptions have also added 120 km² of

new land and are a major tourist attraction

Eruptions occurred continuously from May 5th

until May 28th. No-one was killed but people

fled to the neighbouring town of Icod

Lava poured in 7 separate cascades

over the steep scarp above Garachico

and completely filled the harbour

The stronger basaltic flows buried orchards,

blocked springs, set fire to many houses,

overwhelmed the finest quarter of Garachico

and spread into the sea as a fuming lobe

The town was re-built over the next few

decades more or less to the same town

plan on the surface of the new lavas

Lava Flows – Garachico, Tenerife 1706

La Garachico on the North Coast viewed from the road above (C820)

The original town was largely destroyed in 1706 by lava erupted from the

cone of Montana Negra 6.5km away and 1300 metres above the town

The town has been re-built on the lava

apron formed as the lava plunging

down the cliff reached the sea

Lava Flows – Laki, Iceland 1783-1784

Largest recorded historical eruption

Total volume of basalt extruded was

14.7 km³, covering an area of 565 km²

A few churches, farms and homesteads

were damaged but no-one was killed directly

Lava Flows – Nyiragongo, Congo January 10th 1977

A lava lake of basalt emptied following a large fissure-type eruption

Initial speed of travel of lava flows were 100 km per hour

Lavas covered 20km² and killed several hundred

people and wildlife including a herd of elephants

Lava lake in Nyiragongo crater

had been filling up for 50 years

Lava lake just prior

to the 1977 eruption

Lava Flows – Flood Basalt Eruptions

Mega eruptions of basalt which

have been correlated with mass

extinctions in the geological record

No Flood Basalts have occurred since

man evolved just 4 million years ago

Last Flood Basalt was 15 Ma in the

Columbia River Plateau in the USA

The volume of basalt erupted was

1,500 km³, some flows travelled

up to 300km from their source

Lava Flows – Flood Basalt Eruptions

The Columbia River Plateau is a small

Flood Basalt eruption compared to

those erupted in India and Siberia 65

and 250 million years ago respectively

The Deccan Trappes in India contain

enough basaltic lava to cover the whole

of the USA to a depth of 1 kilometre!

‘Flood’ basalt provinces:

locations in red

Province Age

(Myr)

Volume

(millions of km3)

Paleolatitude Duration

(Myr)

Columbia River 16 ± 1 0.25 45oN ~ 1 (for 90%)

Ethiopia 31 ± 1 ~ 1.0 10oN ~ 1

North Atlantic 57 ± 1 >1.0 65oN ~ 1

Deccan 66 ± 1 >2.0 20oS ~ 1

Madagascar 88 ± 1 ? 45oS ~ 6?

Rajmahal 116 ± 1 ? 50oS ~ 2

Serra Geral/ Etendeka 132 ± 1 >1.0 40oS ~ 1 or ~ 5?

Antarctica 176 ± 1 >0.5 50-6oS ~ 1?

Karoo 183 ± 1 >2.0 45oS 0.5 - 1

Newark 201 ± 1 >1.0? 30oN ~ 0.6

Siberian 249 ± 1 >2.0 45oN? ~ 1

‘Flood’ basalt provinces:

flood for thought

K/T ?

Pyroclastic Flows

A mixture of hot rock fragments, lava

particles and ash buoyed up by hot gases

Often called Nuées Ardentes or glowing fire-clouds

Associated with andesitic and rhyolitic

volcanoes and the collapse of lava domes

Can move at high speeds up to 300 km per hour

and can extend up to 40km from their source

Temperatures within the flow

are commonly 100-700°C

Redoubt Volcano-Alaska with a growing Lava Dome February 1990

The lava dome was destroyed by an eruption on

February 15th 1990 which generated a pyroclastic flow

Lava Dome on the North

face of Redoubt Volcano

Pyroclastic Flow – Augustine Volcano, Alaska 1986

Geologist inspects the pyroclastic flow, note the

wide range of particle sizes all deposited together

Pyroclastic Flows – Mount Pelée 1902

Only 64 known survivors from 29,000

inhabitants of the port of St.Pierre

Many sources state only 1 or 2 survivors which

is now known to be incorrect following the

publication of La Catastrophe by Alwyn Scarth

A pyroclastic flow was generated on May 8th

1902 which sped down the River Blanche

valley at a speed in excess of 190 km/hr


The pyroclastic flow has been

estimated at 700°C which was hot

enough to melt glass and metal

Further Nuées Ardentes occurred

on May 20th and also August 30th

1902 killing another 2000 people


A famous survivor of St.Pierre was Louis-Auguste

Ciparis, a prisoner who had been put into solitary

confinement in a small cell built like a bomb shelter

The structure still survives today


Left, the 25 year old Louis-

Auguste Ciparis still quite

badly burned a month after

his release from prison

Below, drinking glasses

partially melted by the fires

that raged in St.Pierre after the

Nuée Ardente on May 8th 1902

Pyroclastic Flows – Mt. St.Helens May 1980

Before the eruption of May 1980


After the Eruption of May 1980

New lava dome

beginning to form


Northern flank of the mountain rose 150m

under the force of magma rising inside

A near surface earthquake magnitude 5.1

caused the collapse of the northern slope

The avalanche and associated explosion

decapitated the cone and created a

crater 600m deep and 2km in diameter

The pyroclastic flow was dubbed the ‘Stone Wind’ by

the media and it reportedly travelled at supersonic

speed and had a temperature of 250°C


600 km² of forestry was devastated

by the pyroclastic flows

Close to the volcano, full grown Douglas

Fir trees were blasted off their stumps

At 30 km away the trees were pushed

over and oriented parallel to one another


30km away from the eruption of Mount St.Helens


Large bulldozer wrecked by the

pyroclastic flow of May 18th 1980

The pyroclastic flow

contained large boulders

up to 1 metre in diameter


Before After

The same marker pole

Volcanic Dust, Ash and Tephra

Dust – Pyroclastic air fall

material <0.5mm in diameter

Ash – Pyroclastic air fall

material <2mm in diameter

Tephra – Pyroclastic air fall

material >2mm in diameter

Volcanic Dust, Ash and Tephra

Ash build up on roofs can lead to their collapse

300 people were killed by this method during the

eruption of Mount Pinatubo, Philippines 1991

Ash infiltrates machinery and quickly

wears out any moving parts

Fine ash from an eruption is hazardous to aircraft-when

heated inside a jet engine it creates a liquid that sprays

around the turbine and sets as a glassy coating which

blocks the airflow and shuts down the engine.

Nine jets had to make emergency landings

during the month after the 1991 Pinatubo

eruption having flown into the ash cloud

Problems created by air fall ash deposits

The Philippines after Pinatubo erupted Montserrat after Souffriere Hills erupted

Japan following Mt.Unzon eruption The Philippines after Pinatubo erupted

Ash deposits from Galunggung, Java, August 1982

Terraced fields covered in ash buries and

kills crops leading to local food shortages

Toxic chemicals in the ash may poison the soil

Ash from Galunggung, Java Shopping in Washington State May 1980

Ash fall can turn day into night

and make driving hazardous

Ash and dust inhalation leads

to respiratory problems

Volcanic Gases - Hawaii

Volcanic Gases – Laki, Iceland 1783-1784

Basaltic lavas 14.7 km³ in volume also

emitted 8 million tonnes of fluorine gas

About 122 million tonnes of sulphur

dioxide was released in columns that rose

6-13 km high and generated 250 million

tonnes of sulphuric acid aerosols that

remained aloft for about 2 years

Volcanic Gases – Laki, Iceland 1783-1784

Fluorine gas contaminated pastures

and over 75% of the sheep and horses

plus around 50% of the cattle died

Crops failed, famine ensued and over

20% of Iceland’s population died

The aerosol spread as a blue fog and caused

crop failure in Ireland and Scandinavia

The aerosol also caused three long and

abnormally cold winters in the northern

hemisphere from autumn 1783 to spring 1786

Two-stage

degassing in

flood lavas

Laki plume transport in first month

Polar jet stream

Temperature

anomalies in

NW Europe

July 1783 temperature

deviations from the

1768-98 mean (in K)

+3

+2 +1 0

Pinatubo sunset

over Hawaii

Volcanic aerosol

Optical phenomena & weather effects

following the eruption of Tambora 1815

William Turner.

Pendennis Castle, Cornwall;

Scene after a Wreck. c.1816

T Cobbley et al.

Amazing skies, England,

1815-1816

Volcanic Gases – Lake Nyos, Cameroon August 21st 1986

Lake Nyos is a small but deep lake filling the crater of

an active hot spot volcano in Cameroon, West Africa

Volcanic Gases – Lake Nyos,

Cameroon August 21st 1986

Lake Nyos is 1km wide and 200m deep

and fills the crater of a hot spot volcano

Because of its depth, the cool bottom waters

do not mix with the warmer surface waters

For many years the two waters

remained separate from each other

During this time carbon dioxide slowly

bubbled out of cracks in the crater floor

and dissolved in the cool bottom water

Volcanic Gases – Lake Nyos,

Cameroon August 21st 1986

By August 21st 1986 the bottom water had

become supersaturated with carbon dioxide

On that day, perhaps due to an earthquake or

storm, the lake burped, expelling huge bubbles

of carbon dioxide (1 cubic km of gas)

The gas being denser than air flowed down the

flank of the volcano and spread out over the

countryside for about 23km before dispersing

The gas cloud engulfed the village of Nyos killing

1,742 people and around 6,000 head of cattle

Volcanic Gases – Lake Nyos, Cameroon 1986

Cattle near Lake Nyos, Cameroon, West Africa, fell

where they stood, victims of a cloud of carbon dioxide

Volcanic Gases – Nyamuragira Volcano, Zaire

Dog skeleton found on the southern flank of Nyamuragira volcano

in a ‘Mazuku’ a Swahili word for a pocket of carbon dioxide gas

Volcanic Gases – Volcanic Smog (Vog) - Hawaii

High pressure – cold dense air is descending

Volcanic gases are unable to escape through it and accumalate

as a volcanic smog (vog) a few hundred metres above the ground

Secondary Volcanic Hazards

Lahars

Volcanic Landslides

Tsunamis

Lahars – Volcanic Mudflows

Volcanic ash mixes with water

to form a dense slurry similar

to freshly mixed concrete

The slurry known as a lahar can flow

downslope at over 50 km per hour

The water may be derived from melted

snow and ice from the upper part of

the volcano, from heavy rainfall or

from the collapse of a crater lake

Lahars – Nevado del Ruiz, Colombia 1985

The town of Armero in Colombia was overwhelmed

by lahars from the Nevado del Ruiz volcano

Although more than 20 km away from the volcano over

22,000 people were killed in Armero buried alive in the 8m

deep lahars that travelled at speeds of up to 45 km per hour

Armero

Lahars – Nevado del Ruiz, Colombia 1985

The eruption melted the ice cap as it was showered

with hot pyroclastic debris and released between 10

and 60 million cubic metres of water

90% of all buildings in the town were destroyed, replaced

by a 5-8 metre thick layer of mud which now entombs the

bodies of around 25,000 people and 15,000 animals

Lahars – Volcanic Mudflows

Armero

Armero Armero

Bridge destroyed by a lahar from Mount

St.Helens, Washington State, USA

Lahars – Redoubt Volcano, Alaska 1989 -1990

Section through 3 successive lahars, material ranges

in size from mud through sand and up to boulders

Lahars – Redoubt Volcano, Alaska 1989 -1990

Mouth of the Drift River, Alaska,

house buried by a lahar

Lahars – Redoubt Volcano, Alaska 1990

Large block of glacier ice carried many kilometres

downstream by lahars in the 1989-1990 eruption sequence

Lahars – Redoubt Volcano Alaska 1990

These tanks escaped damage but a total of $160 million

in damages to petroleum installations occurred nearby

On February 15th 1990 containment berms at the

Drift River Oil Terminal were over-run by a lahar

Tsunamis

Generated by explosive eruptions on volcanic

islands or by submarine caldera collapse

Waves generated may reach tens of

metres up to 100 metres in height

Most of the 36,000 deaths attributed to

the 1883 eruption of Krakatoa were not

due to ash or lava, but to tsunamis that

slammed into nearby coastal towns

Tsunamis

Submarine volcanic

eruption, caldera collapse

or volcanic landslide

Tsunamis – Krakatoa 1883

Maps showing islands in the Krakatau group before and after the eruption

The eruption sequence generated many tsunamis,

between 30 and 40 metres in height which are reported

to have moved at an average speed of 60 mph

Eruptions followed

by caldera collapse Before

After


All coastal towns and villages on the Sunda

Strait were destroyed within 2 hours of the

explosion and collapse of the volcano

The waves were so powerful that

blocks of coral weighing up to 600

tonnes were thrown onto the shore

The warship Berouw was carried 3km

inland and deposited at an elevation

of 10 metres above sea level


The warship Berouw, well

and truly stranded 3km up

the Koeripan River. Hunks

of rusting iron remained in

the jungle until the 1980s.

The Royal dutch Navy’s armed

paddle steamer Berouw about

to be picked up by one of the

large tsunamis generated

by the eruption

Evidence of Past Tsunamis-The Sediment Record

Tsunami

Deposit

Tsunamis – The impact on low-lying coastlines

Volcanic Landslides

These are gravity-driven slides of masses

of rock and loose volcanic material

Often occur during an eruption, as

with Mount St.Helens when the North

side of the volcano collapsed

Landslides can occur at other times on volcanic

craters as a result of heavy rainfall or earthquakes

A chaotic tumbling flow of material

is termed a debris avalanche

Ground deformation of volcanic slopes by

rising magma may also cause instability and

trigger landslides before an eruption

Shaded relief view of the Canaries from the West

Arrows indicate debris avalanche deposits from giant landslides

The Orotova and Guimar Valleys

Both are 10km wide with smooth

floors sloping gently seawards

The landslides that formed them

displaced more than 100km³ of lavas

with a total thickness of 150-600m

These displaced lavas now lie on a

layer of chaotic breccia and sandy

clay that was crushed when the

volcanic materials slid over them

Volcanic Landslides - Tenerife

Figures refer to

dates of eruptions

Volcanic Landslides -Tenerife

volcanic landslides

The End

Eruption cloud of Redoubt Volcano, Alaska April 21st 1990

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