Volcanic Hazards - Tasker...
Transcript of Volcanic Hazards - Tasker...
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
5000 (pyroclastic flows)
1930, Merapi, Indonesia
1400 (pyroclastic flows)
1951, Lamington, PNG
3000 (pyroclastic flows)
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
Pyroclastic Flows – Mount Pelée 1902
Pyroclastic Flows – Mount Pelée 1902
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
Pyroclastic Flows – Mount Pelée 1902
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
Pyroclastic Flows – Mount Pelée 1902
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
Pyroclastic Flows – Mt. St.Helens May 1980
After the Eruption of May 1980
New lava dome
beginning to form
Pyroclastic Flows – Mt. St.Helens May 1980
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
Pyroclastic Flows – Mt. St.Helens May 1980
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
Pyroclastic Flows – Mt. St.Helens May 1980
30km away from the eruption of Mount St.Helens
Pyroclastic Flows – Mt. St.Helens May 1980
Large bulldozer wrecked by the
pyroclastic flow of May 18th 1980
The pyroclastic flow
contained large boulders
up to 1 metre in diameter
Pyroclastic Flows – Mt. St.Helens May 1980
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
Tsunamis – Krakatoa 1883
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
Tsunamis – Krakatoa 1883
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