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Impact of eruptions
Vo l ca noe
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Prediction
Part II
Supervolcanoes

Prediction of Volcanic Eruptions
Identify volcanoes and the frequency and style of their
eruptions (a geological problem).
Long Term Prediction
Establish the level of risk based on historic and geologic
record.
Establish probabilities of eruption, style and location for
individual volcanoes.
E.g., for individual volcanoes: determine most likely routes
for lahars, nuees ardentes, lava flows, etc., and avoid
construction in those areas.

Short-term prediction
Based on the recognition of a pattern of events prior to
previous eruptions.
Gas emissions: rates of emission and type of gas changes in
some volcanoes.
Important gases include sulfur dioxide (SO2) and carbon
dioxide (CO2)
Changes in concentration may reflect movement of the
magma up the vent.

Surface tilting: recognition of changes in the land
surface due to building pressure in the conduit.
A surface bulge appeared on Mt. St. Helens prior to its
eruption.
April 26 May 2
April 8, 1980

Earthquakes: generated as the magma moves up the
feeder conduit to the vent.
When viscous magma becomes stuck in the conduit strain
energy builds as more magma tries to push out.
Movement takes place in a series of “jerks” as the rock
material breaks. Each “jerk” produces an earthquake.
Magnitudes generally less than 5 M.
The more earthquakes the further the magma has moved.

Mount Spurr, Alaska:
The 1992 Eruption of Crater Peak Vent
USGS
Black bars: earthquake
frequency.
Red lines: volcanic eruptions.

A combination of approaches is likely the key to short-term prediction.

The impact of volcanic eruptions

Volcanic Hazards
Damage limited to the vicinity in the immediate area of the
volcano.
Lava flows
Commonly destroy property in Hawaii and Iceland.
Fatalities rare due to slow
speed of advancing lava
flow.

Ash fall
Extensive property damage and fatalities can result from
heavy ash falls.
Significant ash in the upper atmosphere can circle the
globe in a matter of weeks.
Mt. St. Helens’
ash cloud
More than 80 commercial jets have been damaged by
flying through volcanic ash clouds.

Pyroclastic flows
Lahars can also dam rivers and which can lead to
extensive flooding.
Lahars are fast moving mudflows that can inundate
urban areas that are nearby the eruption.

Lahars can be the most devastating outcome of many
volcanoes.
Water and debris rushed down the slopes, picking up more
debris along the way.
A relatively small eruption of Nevada del Ruiz, Columbia,
in 1985, generated a lahar when the volcano melted a 2.5
km2 area of snow and ice.

A 5 metre wall of
water and debris
slammed into the town
of Amero, 72 km from
the volcano.
The lahar killed
28,700 people and
destroyed over 5,000
structures in the city.

Nuée ardentes destroy life and property in their paths.
60 people, thousands of animals and fish, and
hundreds of acres of lumber were destroyed by ash
flows from Mt. St. Helens.
A Nuée Ardent killed 20,000 people when Mt. Vesuvius
exploded and shed a pyroclastic flow across the village
of Pompeii in 79 AD.

People and animals
died instantly from the
rushing cloud of hot
gas and ash.

Landslides
Landslides can be generated when a volcano collapses
during an eruption.
During the Mt. St. Helens eruption 2.3 km3 of debris slid
down the mountain at speeds up to 240 km/hr.
The slide traveled over 24 km and left a 45 m deep deposit.
350,000 years ago Mt. Shasta experienced a similar
eruption and landslide that was 20 times greater than that
of Mt. St. Helens.

Volcanic Gases
In addition to making magma more explosive, volcanic eruptions also
include gases that can be deadly to all life.
CO2, SO2 and CO are the most abundant of harmful gases.

Volcanoes release more than 130 to 230 million tonnes of
CO2 into the atmosphere every year
Humans add CO2 at the rate of approximately 22 billion
tonnes per year (150 times the rate of volcanic production)
Human CO2 production is equal to that if 17,000 volcanoes
like Kilauea were erupting every year.
SO2 emissions can have direct effects on life in the vicinity
of a volcano.
An eruption in 1783 of Laki Crater (Iceland) produced a
sulfurous haze that lasted for 9 months and killed 75% of
all livestock and 24% of the Icelandic population.

Mammoth Mountain is
a relatively young
volcano that is emitting
large volumes of CO2.
Gas concentrations in the soil in
some areas near the mountain are
high enough to kill trees and small
animals.

If the air that we breath has more than 10% CO2 it
becomes deadly because it displaces the Oxygen that we
need for respiration.
Lake Nios, Cameroon, is a very deep lake within a volcanic
crater.
The lake is so deep that hydrostatic pressure forces CO2 to
remain at the lake bottom.
When the pressure of the CO2 exceeds a certain limit the
gas rapidly bubbles up out of the lake and flows as an
invisible gas cloud down the adjacent slopes.
On August 61, 1986 such a gas release flowed 19 km
suffocating 1,700 people along its route.

The fountain in the
background lifts CO2
up to the surface so
that it no longer
accumulates.
Lake Nyos 10 days after
the 1986 eruption

Tsunamis
Caused by the displacement of seawater by eruptions
of volcanic islands and submarine volcanoes.
Krakatoa (1883 eruption) killed 36,000 people by the
tsunami, alone (the most deadly outcome of the
eruption).
This is the newly forming
summit of Krakatoa, growing
where the 1883 eruption blew
the top off of the original
volcano.

Global Climate Change
Due to ash and gas that may spend years in the upper
atmosphere; reduces incoming solar radiation.
SO2 from an eruption forms tiny droplets of sulfuric acid
in the upper atmosphere.
The droplets significantly increase global albedo…..a
negative radiative forcing that leads to cooling.
Mt. Pinatubo (1991) released 22 million metric tons of SO2
and reduced the Earth’s average temperature by 0.5
degrees Celsius in the year following the eruption.

Tambora (1815 eruption) was followed in 1816 by the
“year without a summer”.
Average global temperature is estimated to have been
reduced by 3 degrees Celsius.
A series of eruptions of Tambora (Indonesia) extruded up
to 150 km3 of magma (solid equivalent), much of it into the
atmosphere.

Food shortages and starvation are attributed to the deaths
of 80,000 people.
In June of 1816 there was widespread snowfall throughout
the eastern United States.
The normal growing season experienced repeated frosts
as cold air extended much more southerly than normal.
The global population was about 1 billion people in 1816.
Our current population is a little over 6 billion.
The 1816 fatality rate would have resulted in a death toll of
nearly 500,000 people due to starvation.

Deadly Historic Volcanic Eruptions
A stratovolcano along
the Caribbean trench.
Mt. Pelée
(West Indes)
VEI = 4

Lava domes are constructed of
viscous lava and are prone to
collapse, unleashing a violent
pyroclastic flow.
An eruption in 1902 following the
growth of a lava dome on the side
of the mountain.

The nuée ardente that was generated
when Mt. Pelée erupted swept 6 km
downslope through the town of St.
Vincent.

Almost the entire
population of 30,000
people were killed
within minutes of
inhaling the hot gases
and ash.
There were only two
survivors; one was in a
dungeon!

Tambora (1815) VEI = 7
The largest eruption of historic time.
Greatest impacts from pyroclastic flows and
ash and gas eruptions.
Approximately 150 km3 of ash was erupted
with the explosions.
10,000 people were killed by bomb impacts, tephra falls and
pyroclastic flows.
By far the largest impact was on the Earth’s atmosphere.
The eruption plume reached 44 km above the earth, loading the
stratosphere with ashes and gases.

The concentration mercury
in ice cores from glaciers in
Wyoming record a peak in
atmospheric mercury that
corresponds to the Tambora
eruption.
The atmospheric impact
caused the “year without a
summer” along with 80,000
deaths due to famine and
disease.

Krakatoa (1883)
On the Island of Rakata, Krakatoa was one of
130 active volcanoes in Indonesia (the country
with the most active volcanoes in the world).
The volcano had been inactive for almost 200
years prior to a series of small eruptions that
began in 1883.
VEI = 6

The volcanoes of Indonesia are due to the northeastward subduction
of the Indo-Australian plate beneath the Eurasian plate.
Stratovolcanoes with a high probability of violent eruption.

Krakatoa began its eruptive stage on May 20, 1883 immediately
following a strong earthquake (no sensors were there to measure it).
The first explosions were heard 160 km away and sent steam and ash
upwards to a height of 11 km.
By August 11 three vents were active on the volcano.
On August 26 several loud eruptions
took place over the course of the day
sending dust and ash to over 25 km
elevation into the atmosphere.

On August 27, four very large eruptions began at 5:30 am.
The last of the four was the largest and could be heard from Sri
Lanka to Australia, up to 4,600 km from the volcano.
A 23 km2 area of the island was gone following the fourth eruption.

Super Volcanoes
While not defined officially, lets say any eruption that ejects 1000
km3 or more of pyroclastic material (i.e., VEI 8 or more).
According to M.R. Rampino super eruptions take place, on average,
every 50,000 years. Three of the best known eruptions are compared
below.

Toba: the world’s largest Quaternary caldera.
The Australian Plate is subducting
beneath the Eurasian plate at a rate
of 6.7 cm/yr.

Today Toba is a caldera or
depression that is occupied
by Lake Toba.
It is 100 km long and 30 km
wide.
Toba last erupted about
75,000 years ago with the
largest eruption of the last 2
million years.

840,000 years ago
500,000 years ago
Three eruptive events have been
recognized.
74,000 years ago
Each producing a caldera.
Samosir Island, rising 750 m above
the lake, is a dome built from lava
following the last eruption.

The eruption ejected 2,800 cubic km of material and the pyroclastic
flows covered an area of at least 20,000 square km.
In the immediate vicinity of the volcano ash deposits reach 600 metres in
thickness
Ash fall from the eruption covers an area of at least 4 million square km;
half the area of the continental United States.
Global cooling is estimated at between 3 and 5 degrees Celsius with
regional cooling of 15 degrees C.
Tropical plant life would have been all but eliminated
Temperate forests would loose 50% of all trees.

It is estimated that the growing population of homo sapiens (i.e., us) was
reduced from 100,000 individuals to as few as 3,000 individuals (97% of
all humans were lost!).
This reduction had been estimated for approximately the time of Toba’s
eruption on the basis of genetic studies and is termed the “human
population bottleneck”.

Yellowstone Caldera
Known for its hot springs and geysers,
Yellowstone National Park, is likely
the most popular super volcano in the
world.
The park sits on an active caldera that
rises and sinks in response to magma
movement and pressure fluctuations
within the Earth.
Over recent years the surface has risen
by as much as a metre and sunk back
by 1/3 of a metre.
Thousands of small earthquakes are
produced as earth surface moves.

The magma chamber is only 5 to 13 km below the land surface.
The caldera is 80 km
long and 50 km wide.

The caldera and its magma chamber are due to a hot spot in the mantle
that has moved several hundred kilometres over the past 12.5 million
years.
The movement is due to the drift of the north American continent over
the hot spot.
Ancient, inactive
calderas mark the path
of the hot spot.

The current caldera was formed with an eruption 640,000 years ago (the
Lava Creek Eruption).
This eruption ejected 1,000 km3 of pyroclastic debris.
An earlier eruption (the Huckleberry Ridge Eruption, 2 million years
ago) ejected 2,500 km3
of pyroclastic debris.
A smaller eruption
happened 1.3 million
years ago, releasing
280 km3 of debris.

Eruptions appear to have a 600,000 year period (that long between
eruptions) so we’re overdue for another one.
Previous eruptions spread ash over thousands of km2 across the US.

Heightened monitoring of the Yellowstone Caldera in recent years has
led to media concern of an impending eruption.
Government officials and geologists indicate that there have been no
clear indicators of high risk at this time.
If such an eruption were to take place, North America and the rest of the
world could experience another “Dark Ages”.

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