BBC SCIENCE
RESEARCH DOCUMENT
SUPERVOLCANO
DEVASTATING EFFECTS OF ASH FALL
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CONTENTS
1. Mission
Page 1
2. Historic Data
Page 2
3. UK Met Office
Page 4
4. Effects
Page 5
5. Global Ash
Page 7
6. Ash Detection
Page 7
7. Positive Uses for Ash
Page 8
8. Ash and Health
Page 8
9.
10. Met Office Models
Page 9
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ASH FALL
Experts Consulted
Prof Bill McGuire - Head of Benfield Greig Hazard Centre, University of London
Derrick Ryall – Volcanic Ash Advisory Centre (VAAC), UK Met Office
Grace Swanson - Senior Meteorologist and VAAC manager, NOAA
Prof Mike Perkins – University of Utah
Prof Barbara Nash – University of Utah
Philip Schneider – Director, Multihazard Loss Estimation Program, National Institute
Of Building Sciences
Barbara Schauer - Project Manager, National Institute of Building Sciences
Claire Drury – Project Manager, HAZUS loss estimation project, FEMA
1. MISSION
We needed to get a realistic picture of the ash distribution after a Super-eruption. Ash
is one of the major hazards after an eruption and the amount and extent of the ash
fall was important to establish for our scenario. Once we had a picture of a possible
ash fall map we would be able to understand the effects of a Super-eruption in the
modern world.
In order to get a good picture of how Northern USA could be covered with ash, we
first went to the historic records for past Yellowstone events. We have decided to
model this event on the first Yellowstone eruption that occurred 2 million years ago.
2. HISTORIC DATA
Prof Perkins and Prof Nash from University of Utah have produced ash fall
information on this event which is present in the book ‘Windows into the Earth’. They
state it is a speculative attempt to show the primary thickness of ash generated
during the eruption 200 million years ago.
1. The volume of uncompacted ash-fall from the volcano is 1000 cubic kilometers
2. The distribution of most of the ash-fall is approximately the same as the known
distribution of the ash from the super-eruption 200 million years ago.1
3. The thickness at the site of the eruption is about 3 meters and the thickness at the
known margin of the Huckleberry Ridge ash-fall layer is about 2 centimeters.
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As shown by the work of Izett and Wilcox (1982).
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Map 1: Perkins Ash distribution map
From this map and various other data we were able to produce the following table for
possible ash depths for an eruption releasing 1000 cubic km of uncompacted ash.
Compacted ash would fall out of the sky very quickly so that is why it is important to
only consider the uncompacted ash.
Table 1: Maximum / minimum depth and
Distance
blast (km)
40
from Ash Thickness (cm)
Towns/Cities
335.5 (~11 ft)
West Yellowstone, Mammoth
80
125
274.5 (~9ft)
183 (~6ft)
Gardiner, Grayling
Bozeman, Cody
150
122
Idaho Falls
200
300
375-800
Beyond this
91.5 (~3ft)
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(~2ft)
15.25 (~6”)
6” down to 1”
(~4ft)
Salt Lake City
Denver, Portland, Seatle
LA, Santa Fe, Dallas, Chicago
etc.
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By plotting this information on a graph (see below) it is possible to see the potential
drop off in ash depth the further away from the event you get.
Graph to show
Ash Deposition for 1st Yellowstone Eruption 200
mya
400
300
Amount of ash
200
(cm)
100
0
40
80
125
150
200
300
375
800
Distance from eruption (km)
3. UK MET OFFICE
To ensure this model is accurate and matches today’s weather patterns The UK Met
Office Volcanic Ash Advisory Centre (VAAC) conducted some models for us based
on a June eruption of 1000 cubic km of uncompacted ash. In our scenario the Supereruption occurs in June so it is important to model during this time as the jet stream
operates at different speeds during the winter months. The model they use is called
NAME.
The Met Office state that they used UK Met office data (winds/rain etc) from June 1020 this year to simulate an eruption. Using the figure of 1000 cubic km over 7 days
and assuming density of ~3 grams of ash per cm3 they used a specified release rate
and assumed a 'typical' particle size distribution. The ash column is assumed 30km
high and across an area of 50km.
Importantly as well as knowing the distribution we needed to know the depth of ash
fall on the ground or deposition. The Met Office also produced a map from NAME
that estimates the amount of material deposited to the ground. If we assume a
density of ash fall as ~1g per cm3 we can estimate ash thickness. The maximum
values given are localised.
Overall the data provided by the Met Office is surprisingly consistent with the figures
suggested by the data for historic events. It is also worth noting that a lot of ash is
predicted to come out in rainfall (an efficient process for removing particles from the
atmosphere). This is the case over the UK and Europe.
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This is just one simulation for one day in June and each time you do the simulation
you will get a slightly different result, but it is a proof of concept. It is reassuring that
the map and ash amounts are broadly consistent with the Perkins source - the main
difference being the high variability caused by the changing weather situation.
The ash model produced by the met office can be seen at the end of this document.
It shows the release of ash on day one and the distribution of ash over the following
12 days. Generally the ash movement will be West to East although locally there will
be a weather feature that can drag some stuff back to the West. On average the wind
will be west to east and will be caught up in a westerly flow. Whether this will hit
Canada or Florida is anyone’s guess it will depend from day to day. In our scenario
there will not be much ash hitting Canada and Florida not be affected massively by
the ash fall.
The model shows the ash will reach across the Atlantic and will reach Europe within
3 or 4 days, this corroborates with the timings that other scientists have told us about.
Typically it will be caught up in a band of latitudes that affect the UK and Europe at
some point or other.
There are three ways that the ash deposits out.
i) natural mixing of air – dry deposition
ii) particles that are heavier and larger settle under gravity – sedimentation
iii) material caught up in clouds and help form clouds that get rained out. A lot of what
you see in terms of distribution are rain – Wet deposition (within that there are
various other processes).
4. EFFECTS
Darkness
Looking at concentrations in the atmosphere the model suggests that the cloud might
well be 'visual', (ie significantly reducing sunlight and posing a risk to aviation) right
across America, the Atlantic and into Europe.
The darkness due to the ash will depend on the duration of the eruption. In our
scenario the eruption occurs for 7 days, so while the ash is being pumped out it will
be very dark in the immediate area of the eruption. Where there are thick clouds of
ash moving away from the eruption, darkness would also fall on these areas.
Ash Movement and Disruption
We then need to ask more specific questions about the movement of the ash across
North America and the globe. The answers were based on our experts own
knowledge and observations from past eruptions.
Once ash gets into the atmosphere, it’s carried downwind over hundreds and
thousands of kilometres, remaining airborne for days to weeks. The ash that gets into
the jet stream will spread across the US at twice the speed of a car, 150 miles per
hour, if in the summer. If in the winter, double that. (Maslin)
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The ash fall could reach London in about 3 days. You could even see pockets of ash
falling on a car in London.
Effects on Road
Fine ash fall, even if only a few centimetres thick, may make asphalt road surfaces
slippery, causing traffic congestion on steep slopes or accidents at corners and road
junctions (USGS).
Cars driving faster than 5 miles per hour on ash covered roads stir up thick clouds of
ash, reducing visibility and causing accidents. Roads, highways and airport runways
can be made treacherous or impassable because ash is slippery and may reduce
visibility to near zero.
Effects on Rail
Where the tracks have ash on them the railways will be very dangerous. There would
be worry about derailing etc. As much of the electricity supply could be down again
this would affect the running of the rail system.
Effects on Airplanes
Planes have dropped out of the air during regular volcanic eruptions, e.g. during the
Pinatubo VEI 6 eruption.
As it disperses downwind, it becomes increasingly difficult for pilots and scientists to
distinguish eruption clouds visually from weather clouds, especially at night or in poor
weather. Since ash cannot yet be detected by weather radar aboard aircraft, satellite
images and pilot reports of unexpected ash encounters provide the critical
information needed to keep commercial aircraft from entering an eruption cloud.
In June 1982 a British Airways 747 lost all four engines and suffered severe damage
on encountering ash from Mt Galunggung in Indonesia, descending to 12 000 feet
before being able to restart some engines and make an emergency landing in
Jakarta. Three weeks later the same thing happened to a Singapore Airlines 747,
which this time lost two engines and also made an emergency landing. Since then,
there have many aircraft encounters with volcanic ash.2
You could probably get planes up in the sky again – within a couple of days of the
eruption stopping you could fly again, however this would only be in the outer areas
where there was no ash in the sky. Much of the US would not have planes flying over
for weeks and in some cases months. Whenever ash is blown up into the sky the
suspended as will cause a problem for aviation, so there will be continual hazards. .
Effects on Buildings and utilities
Ash also clogs filters used in air-ventilation systems to the point that airflow often
stops completely, causing equipment to overheat. Such filters may even collapse
from the added weight of ash, allowing ash to invade buildings and damage
computers and other equipment cooled by circulating air outside.
The amount of ash needed to collapse a building is approximately 30cm – less if it’s
2
http://www.bom.gov.au/info/vaac/
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Wet. A dry layer of ash 10 cm thick weighs 120 to 200 pounds per square yard, and
wet ash can weigh twice as much. The load of ash that different roofs can withstand
before collapsing varies greatly – flat roofs are more likely to collapse than steeply
pitched ones.3
Communications
Eruption clouds and ash fall commonly interrupt or prevent telephone and radio
communications in several ways, including physical damage to equipment, frequent
lightning (electrical discharges) and either scattering or absorption of radio signals by
the heated and electrically charged ash particles. 4
Levels of Ash
Less than 1 mm ash thickness:

Will act as an irritant to lungs and eyes.

Airports will close due to the potential damage to aircraft.

Possible minor damage to vehicles, houses and equipment caused by fine
abrasive ash.

Possible contamination of water supplies, particularly roof-fed tank supplies.

Dust (or mud) affects road visibility and traction for an extended period.
1-5 mm ash thickness:
Effects that occur with < 1 mm of ash will be amplified, plus:
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
Possible crop damage.

Some livestock may be affected. Most will not be unduly stressed but may
suffer from lack of feed, wear on teeth, and possible contamination of water
supplies.

Minor damage to houses will occur if fine ash enters buildings, soiling interiors,
blocking air-conditioning filters, etc.

Electricity may be cut; ash shorting occurs at substations if the ash is wet and
therefore conductive. Low voltage systems more vulnerable than high.

Water supplies may be cut or limited due to failure of electricity to pumps.

Contamination of water supplies by chemical leachates may occur.

High water-usage will result from ash clean-up operations.

Roads may need to be cleared to reduce the dust nuisance and prevent
storm-water systems from becoming blocked.
Taken from USGS leaflet.
Taken from USGS leaflet on Ash fall
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
Sewage systems may be blocked by ash, or disrupted by loss of electrical
supplies.
Damage to electrical equipment and machinery may occur.
5-100 mm ash thickness:
Effects that occur with < 5 mm of ash will be amplified, plus:

Burial of pasture and low plants. Foliage may be stripped off some trees but
most trees will survive.

Most pastures will be killed by over 50 mm of ash.

Major ash removal operations in urban areas.

Most buildings will support the ash load but weaker roof structures may
collapse at 100 mm ash thickness, particularly if the ash is wet.

Road transport may be halted due to the build up of ash on roads. Cars still
working may soon stop due to clogging of air-filters.
Rail transport may be forced to stop due to signal failure bought on by short circuiting
if ash becomes wet.
100-300 mm ash thickness:
Effects that occur with < 100 mm of ash will be amplified, plus:

Buildings that are not cleared of ash will run the risk of roof collapse,
especially large flat roofed structures and if ash becomes wet.

Severe damage to trees, stripping of foliage and breaking of branches.
Loss of electrical reticulation due to falling tree branches and shorting of power lines.
> 300 mm ash thickness:
Effects that occur with < 300 mm will be amplified, plus:

Heavy kill of vegetation.

Complete burial of soil horizon.

Livestock and other animals killed or heavily distressed.

Kill of aquatic life in lakes and rivers.

Major collapse of roofs due to ash loading.

Loading and possible breakage of power and telephone lines.
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
Roads unusable until cleared.
Electrical Discharges
Ash clouds can generate powerful electrical fields producing intense and frequent
lightning discharges, which can interfere with radio communications and damage
electrical installations, or start fires in buildings and installations.
Ash contamination of water supplies
Suspended ash affects the quality of the water supply not only with potable water, but
it also inhibits intake features at water treatment facilities. Turbidity can hinder proper
disinfecting processes (Jonhston, 1994).
Falling ash can inhibit the motors and gears of pumping stations, disrupting the
distribution of water supplies. It contaminates open water sources (ie. lakes, rivers,
streams and reservoirs).
Leachates
Leachates from ash particles release cations and anions into the water. High
concentrations of Cl, SO4, Na, Ca, K, Mg and F are common with lesser amounts of
Mn, Zn, Ba, Se, Br, B, Al, Si, Cd, Pb, As, Cu and Fe. When these elements and
compounds reach certain concentrations they may be dangerous. The chemical
changes often decrease the pH level of the water to harmful levels if consumed by
humans or animals. pH levels have on occasion been measured as low as 5, 7 being
neutral, in water supplies. The extent of contamination is dependent upon the ash to
water ratio.
Fluorine (F-) is a more common volcanic contaminant of volcanic ash. In high
concentrations it inhibits important enzymes in the body from performing their
function. Excess F has been associated with the deaths of livestock.
5. GLOBAL ASH
It is possible for traces of ash to reach the UK, since sand from the Sahara has been
known to reach that far. It is entirely up to what the winds are doing. If it is one big
eruption you are throwing it high into the atmosphere and up into the fastest jet
stream (100 mph mark). If there is a slow high pressure it will hang around for ages.
If you have a raging storm the ash can be carried very quickly. Typically the ash
would be heading towards the East around the world. Locally it can head in any
direction depending what the local weather was doing on that day!
The Met office maps have proved that it is possible for the ash to reach many parts of
Europe. It won’t be experienced to any great extent, but pockets will be obvious.
6. ASH DETECTION
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The Volcanic Ash Advisory Centres (VAAC) around the globe are responsible for
detecting and sending out ash warnings. Their purpose is mainly to warn the aviation
industry but their satellite images and data can also help disaster organisations. In
the US the National Oceanic and Atmospheric Administration (NOAA) have a VAAC
who monitor release of ash from volcanoes.
VAAC are alerted to pre-eruptive activity, and would be on a heightened state of
watching alert having talked to the USGS. Like VAAC, the USGS have call-down
sheets of people to contact in the case of an event – they talk to each other all the
time.
Aviation weather centre in Kansas write SIGMIT briefs for pilots - Not warnings, but
advice on ash. It’s up to the VAA to call the Met office with a warning which is then
issued to the aircraft control centre.
In the event of a large eruption, the aircraft control centre would clear all their aircraft
if it is safe at the time rather than have them grounded. Volcanoes are monitored
every 2 hours or so when not in watch mode. If Yellowstone was on an orange alert
level, they’d be watching it every 15 mins. Rapid Scan Mode (RSM) allows an image
to be taken every 7.5 mins. Super RSM takes a picture every minute. To change the
frequency of images, a call must be placed to the satellite control centre. The US
VAAC team work on 10-hour shifts so that someone is continually monitoring the
images.
If you can’t see what’s happening below the clouds, then you have to rely on models
(done prior to the eruption) which take into account wind conditions. The future of ash
modelling will be standard imaging every 5 mins, rather than every 15, and to have
more steps for different variables (more channels). Polar imaging satellites are too
slow to use as they only give two sets of images every day.
7. POSITIVE USES FOR ASH
Makes a good fertiliser in small amounts. Currently volcanic ash is used as an
abrasive in most hand soaps and household cleaners. Fine grain ash is also used to
finish silverware, polish metal parts prior to electroplating and is used in
woodworking. Volcanic ash may also be used as an essential part of cement. Major
construction projects, such as dams, have been built using a pumice and volcanic
ash mixture in the cement. These materials are also being used in pre-cast concrete
blocks as a light weight aggregate. Many other economic uses have been found,
such as use as filter aids, aggregate in plaster, and as a soil conditioner. The
volcanic ash and dust, which settles into the ground, enrich the soil by contributing
various nutrients. These nutrients help increase the productivity of the soil. [Michegan
Technical University].
8. ASH AND HEALTH
People who have been exposed to breathing air laden with fine silicate dust, possibly
also containing dangerous levels of H2S, CO2 and other volcanic gases will need
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first aid or hospital treatment (USGS). If the ash contains large amounts of the highly
toxic Fluorine, then animals will die an agonising death from Fluoronosis, by ingesting
it (into their stomach).
People can suffocate from the ash, literally drowning in a mix of water and ash. Eg
Tarra Wera, NZ, an eruption under a lake did this. People essentially drowned by
breathing in water and ash.
Cattle normally die of starvation. They can’t get down to the grass because of the
ash, and have nothing to eat, nor anything to drink, so they wander round until they
get too weak, and die.
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9. MET OFFICE MODEL OF ASH DISPERSAL/DEPOSITION
Assuming density of 1g/cm3, we can relate deposition to ash thickness:
1.0e7g/m2 ~ 1000cm
1.0e6g/m2 ~ 100cm
1.0e5g/m2 ~ 10cm
1.0e4g/m2 ~ 1cm
1.0e3g/m2 ~ 0.1cm
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