Volcanoes & the stuff they do
Introduction
Volcanism: Processes whereby magma and associative materials are forced into the
Earth’s crush (intrusive) and/or ejected onto the Earth’s Surface (extrusive).
Instrusive
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Movement of molten magma in the E’s crust
Cools and solidifies within the crush
Intrudes along lines of weakness
Plutonic volcanism
Extrusive
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Movement of magma onto E’s surface thru vent/fissure
Enough force to force crust upwards
Vulcanism is associated with fold mountains/chain of fold mountains such as the
Andes, Rocky’s and Swiss Alps.
Relationship: Volcanism and Plate Tec
Plate movements create fractures in the E’s crust. Magma from the mantle
and melting plates force their way up to the surface to form volcanoes.
Locations
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along subduction boundaries at continental plate-oceanic plate
convergence (Mt. St. Helens) or oceanic plate-oceanic plate convergence
(Philippines and Japan)
along sea floor spreading centres on the ocean floor (Iceland or Mid-Atlantic
Ridge) and areas of rifting on continental plates (rift zones in east asia)
At hotspots, where individual plumes of magma rise to the crust( Hawaii and
Yellowstone National Park)
Distribution of the volcanoes in the world:
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Constructive
o Mid Oceanic Ridge  15%
 Spreading ridges  Volcano
Destructive
o Subduction zones 80%
Hot spots
o Interior of plates 5%
o Mostly in Hawaii
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Circum Pacific (Ring of Fire)
o 2/3 of world’s volcanoes
Medit Region
o Italy, Pompeii
o Another subduction zone of volcanoes
Types of Volcanoes
The type of volcanoes is dependent on the type of lava that forms it, which is
then determined by the crustal material and plate margin the material originated
from. This is because molten magma is really just recycled crustal material (due to
hydration and increases in temperature because it dives into the mantle blah blah).
Volcano
Characteristics
Examples
Flood or
Very liquid lava, flows very widespread, emitted from
Columbia River
Plateau
fractures
Plateau
type
Basalt
In order of
increasing
violence
and
viscosity
Shield
1. Large volcano
Larch Mountain,
Volcano
2. Gentle sloping sides
Mount Sylvania,
3. Formed by basaltic lava with low viscosity and
Highland Butte,
higher temp
4. Lava flows easily and can cover a much longer
distance before it solidifies
Cancelled=
not tested
5. 90% of the volcano is lava rather than pyroclastic
material
6. Found I environments with large supply magma
like hot spots and subduction zones
7. Gentle eruptions- flowing or sputtering lava. Due
to low viscous lava which do not solidify readily
Hawaiian
volcanoes
Mauna Loa of
Hawaii covers
the largest area
while the tallest
measures from
its base to peak
is Mauna Kea of
Hawaii (4.2km)
Cinder
1. Explosive liquid lava emitted from central vent
Famous cinder
Cone/Scori
2. Large
cone =
a Cone
3. Cinder cones grow rapidly
Parictuin. It grew
4. Rarely exceed 250m in height and 500m in
out of a corn
diameter
field in Mexico
5. Sometimes has a collapsed caldera
in 1943 from a
6. Among most common volcanic landforms
new vent. Within
7. Eruptions usually don’t cause any loss of life  not
5 days, it grew
famous
300 feet.
8. Chiefly formed by Strombolian
eruption relatively low-level volcanic eruptions
9. Grow up in groups
10. Occus on flanks of stratovolcanoes and shield
volcanoes
11. Built from lava fragments called cinders
a. lava fragments ejected from a single vent
and accumulate around the vent when
they fall back to earth
Composite/
1. Most common60%
Mt. St. Helens
Stratovolca
2. Common in Subduction Zone
(USA), Mt
no
3. Formed by felsic lava with high viscosity.
Pinatubo and
4. Formed by alternating layers of lava and
Mt. Mayon
pyroclastic material hence “composite”
(Philippines), Mt
5. Lava solidify and pile up easily
Fuji (Japan),
6. Tall conical structure with moderate slope
Gunung Merapi
7. Lava travel short distance
(Indonesia), Mt
8. Felsic Lava high in silica
Vesuvius
9. Violent eruptions of ash and pyroclast due to
viscous magma
o
When very viscous magma rises to the
surface, it clogs the pipe and gas in the
pipe gets locked up intense pressure
buildup
o
Rising magma beneath adds to the press
10. Often form impressive snow capped peaks
o
Exceeding 2500m in height, 1000 sq. km in
surface and 400km cube in volume
11. Large conical shape
12. Steep summit, gentle base
13. Ash and cinder give the steepness of volcano
while lava cements the structure
14. Very quiet between eruptions look like extinct
15. Pyroclastic flow + violent eruption = Most
hazardous to people
16. Violent eruptions cause cracks to develop
secondary cones forming Parasitic
cones/secondary cones/conelets
Volcanic

Very viscous lava
Novarupta.
Dome
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Relatively small
Mount St. Helens
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Can be explosive
Lava dome,
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Occurs adjacent to craters of composite
Mono craters
volcanoes (usually)
Caldera
Very large composite volcano collapsed after an
Crater Lake,
explosive period
New berry,
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Associated with plug domes
Kilauea, Long
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Aka collapsed crator
Valley,
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Medicine Lake,
Yellowstone
Classification of Volcanoes
Types of Volcano
1. See above
Frequency of Eruption
1. Active  constant spilling of smoke, dust and lava; strong smell of sulfur
2. Dormant ’sleeping’. Has not erupted for the past 500 million years
3. Extinct  has not erupted in recorded history
Type of Lava
Lava consists mainly of silica (silicon dioxide). It contains various amounts of
dissolved gases which mostly escape from the lava as it is ejected. The differences in
gases also contribute to the violence of the eruptions, from small lava fountains, to
massive extremely violent explosions.
Mafic lava (basic lava) is very fluid volcanic gases released before they
become explosive. They commonly produce large flows. They can flow as far as
97km, forming low, dome-shaped volcanoes like Mount Loa in Hawaii. Mafic lava
itself usually solidifies into basalt that typically forms smooth billowy masses or tall
hexagonal columns. These columns are called basalt columns and can form some
large plateaus.
Felsic lava is generally less fluid, (or sometimes plugs up the hole entirely) the
pressure of gases and steam tends to build up until the lava is ejected explosively.
They form steep-sided volcanoes. This type of lava solidifies into rhyolite, a finegrained rock resembling granite.
The coolest lava are the felsic lavas, which can erupt at temps as low as 650
– 750 degrees Celsius. Next are andesitic lavas, which erupt at the range of 750 –
950 degrees Celsius. Basaltic lavas are typically erupted at temperatures above 950
degrees Celsius.
Types of Lava
Viscosity
Content of
Silica
Temperature
(relative)
Rate of flow
Basic
- dark
coloured
Low
Low
- also reach in
Fe and Mg
Higher
- 1000 to 2000
degrees
Acidic
– light
coloured
High
High
Lower
- 800 degrees
Readily
- highly fluid
- flows quietly
as
- 16-48km/hr
Slowly
- but more
explosive
- travel further
in the air
- 10-100m/hr
Differences
Basic Volcanoes generally have gentler slopes and are shorter. They however
take up a larger base area. Why does this happen? As basic lava travel much faster
than acidic lava, they can cover a wider surface area. Hence, it will go the
distance, but not increase that much in height. Acidic lava is explosive, it can shoot
the lava vertically pretty high. However, it will land near the crater. As it is slow
moving, it will generally start solidifying near the crater, causing a tall conical
structure with moderate slope, with a steep summit and a gentle base.
Note: Increased Acidity = Increased Explosiveness!
Acidic magma cool slower. When it solidifies, it traps more poisonous gases.
Hence, when the pressure causes them to explode, the shattered rocks and
poisonous gases will contribute to a more violent eruption
Also: Mafic( Magnesium and Feldspar)= Basic Lava = Minerals = Basalt = 50%
silica
Felsic lava = Acidic lava = 70% silica
Intermediate silica content = intermediate lava
Causes of their Formation
Causes of an Eruption/Formation
Rocks formed
from solidified
molten
magma
Ejected onto E’s
Surface
Volcano
matter poured
out
Formation
Movement of
crustal plates
built up
pressure
If vent is
blocked, gases
within magma
expands
Fall back near
vent
Pressure
released along
faults and
fractures
Drives out the
magma as
lava
Magma rises
along these
lines of
weaknesses
Lava may shatter
and form ash,
cinder, dust, etc
(pyroclastic
material)
Accumulation of
Volcanic matter
eventually build up
Volcano!
Volcanoes are formed when there is a convergence or divergence of
tectonic plates.
In the case of divergence, when the two plates move apart, hot magma in
the asthenosphere rises up to take its place, thus forming a volcano. Spreading
ridges and stuff.
In the case of convergence, the denser plate would subduct beneath the
less dense plate. The less dense plate overrides the other. As the denser plate
plunges into the hot asthenosphere, the increase in temperature and hydration from
the sea causes the crustal material to be deformed. However, as the magma
created from this process is less dense than the surrounding solid, it would rise
through the cracks and fractures in the E’s crust onto the surface. As it reaches the
surface, it cools down and solidifies. After some time, the accumulation of these
solidified lava forms the conical shape of volcanoes.
Features /Landforms
Intrusive Volcanism
The important thing to note is that all these differences are brought about
due to the differences in their lines of weaknesses. Weathering can expose dikes and
laccoliths but they’re still intrusive as it is already solidified.
Batholith
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Immense reservoir/mass of magma
Formed at great depth
From the heart/core of mountains (eg. Rockies, the Baths of Virgin Gorda)
Exposed after long periods of erosion
Plutonic rocks (Granite)
Largest intrusive form
Stretch across great length
Laccolith
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Hugh lens-shaped mass og igneous rocks
Lie between layers of sedimentary rocks
Overlying strata forced to arch up in a dome shape, flat bottom
Lopolith
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Saucer shaped mass of igneous rocks
Intrudes along bedding planes of rock strata

A layer of magma that lies between layers of sedimentary rocks or
metamorphic rocks
Several hundred feet thick, many km long
Thin intrusion
Resistant from surrounding rock
Exposed
o Formed steep scarps with flat topped plateau
May find waterfalls
Great Whin Sill (UK)
Sill
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Dyke
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Mass of magma that cuts across bedding planes obliquely/vertically along
joints/cracks
Few cm – hundred metres thick
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Few m – km long
Exposed to form ridge/promontory
o More resistant rocks
o Promontory = prominent mass of land that overlooks lower-lying land or
a body of water
Exposed to form geos
o Less resistant rocks
o Geos = inlet, gully or narrow and deep cleft in the face of a cliff
Igneous rocks are called fire rocks and are formed either underground or
above ground. Underground, they are formed when the melted rock, called
magma, deep within the earth becomes trapped in small pockets. As these
pockets of magma cool slowly underground, the magma becomes igneous
rocks.
Igneous rocks are also formed when volcanoes erupt, causing the magma to
rise above the earth's surface. When magma appears above the earth, it is
called lava. Igneous rocks are formed as the lava cools above ground.
Associated Features
Geysers
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Hot spring which discharges jets of superheated water periodically
Old Faithful Yellowstone National Park (USA)
Fumaroles
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Opening in the E’s crust which emits steam and gases
o Co2, So2, HCL, HSo4
Often found near volcanoes
Lava Plateaus
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Large amt of lava escapes to the surface of E from a fault line
Deccan Plateau  India
Craters
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Large bowl of depression
commonly found on the summit of volcanoes
collection of rain  crater lake
Caldera
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enlarged crater
1km – 10s of km
Causes
o Due to a very violent eruption, the top is blasted away, thus creating a
depression
o Volcanoes sinks after several major eruption
o Removal of magma more than replenishment, causing an empty
chamber and therefore, collapsed crater
Types of Volcanic Eruption
Gentle Sloping Shield Volcanoes
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Fluid, low silica, basaltic magma causes non-explosive fountaining
Lava slows, lava tubes and spatter cones
Magma flows through central cent
Very little ash and gas released
o Kilauea & Mauna Loa Hawaii
Spatter Cones and Ciner Cones
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Mild explosive eruptions; fumaroles
Magma, incandescent bombs, ash and lapilli ejected
Magma-type variable
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Considerable gas build up
o Stromboli (Italy), Paricutin (Mexico), Kivu (Zaire)
Stratovolcanoes
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Hot flows of block and ash
Viscous silica rich magma
Gas rich magma
Voluminous pyroclastic flows
Exceptionally powerful blast from eruptive column
Large amounts of ash ejected. Intense gas build up.
St. Helens (Washington), Mount Pinatubo (Philippines), Krakatau (Indonesia),
Mount Mayon (Philippines)
Changes to the physical landscape
New volcanic features will be ended to the landscape of course, such as
calderas and new volcanoes. The lava would also cover the land. However, the
more destructive impacts are plenty as well.
Destruction:
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Glowing avalanche
o Avalanche of rock fragments mixed with hot lava accompanied by
huge clouds of dust and ash
o 150 kph, 300 – 500 degrees Celsius
 Mt. Pelee, 1902
Asphyxiating Co2 (hot gas)
o 50m thick cloud Cameroon 1986
Mudflows, Lahars and Pyroclastic Flows
o Mixture of ash, pyroclastic materials, soil and water (from craters,
rainwater, melted water)
o Mass movement feature on the slope of the volcano
o Gain more matter as it rolls down the slope
o Move rapidly 1m/s – 40m/s
o Consistency of cement
o Triggered by E’s movement
o Move along river valley
Ashflows
o Ash, dust, gases and fine particles of sand covers extensive area
around the Volcano
Tsunamis
o Huge sea waves
Pollution
o Health of humans, animals and veg affected
o Sound, Air, Water pollution. Destruction of Biodiversity.
Effect on climate

o
o
Fires
Could decrease the temperature as the sunlight is blocked
Sulfur particles cause losses in the ozone
Types of Materials erupted besides Lava
During an eruption, there are other materials that are ejected along with the
hot lava. They add onto the destruction eruptions cause. These are just some
examples
1.
2.
3.
4.
Solid materials ejected during Volcanic eruptions
Ash (<2mm)
Lapilli (2mm – 64mm)
Blocks and bombs (>64mm)
a. size ranged from fine grained fust liked material to large grenade like
objects
5. Gas escaping to the surface through cracks/during eruptions
a. Carbon monoxide/dioxide, sulfurous gases, nitrous gases, steam, etc
6. Lahars
a. Lava + other materials + water
Forecasting Volcanoes
Tiltmeters
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Monitor swells in the volcano by recording the following:
o Changes in the slope angle
o Swelling at the summit
 Can be as little as 1m in 10 years
Earthquakes
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As new magma forces its way upwards, it releases small earthquakes
Seismographs
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As many as 1000 minor/shallow earthquakes/day can be an indication of a
possible eruption
National Volcano Early Warning System
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Robust, real-time monitoring of the most threatening of the Nation’s
volcanoes
A 24/7 Volcano Watch Office
Improved research collaboration between Federal and academic scientists
A National Volcano Data Center
High-quality data sets for volcanological research
observing changes in the temperature and composition of hot springs,
groundwater and volcanic gases, which often alter before an eruption
-
study past trends
Limitations
-
As earthquake activity increased, many seismic signals went off scale, limiting
diagnostic capabilities.
Telemetered deformation instruments could not be installed quickly enough
to capture the deformation signal as magma rose to the surface.
Hot Spot Theory
The hot spot theory was proposed by J. Tuzo Wilson, the Canadian
geophysicist, who discovered transform faults, in 1963. He realized that in certain
locations, volcanism has been active for seemingly no reason. Hawaii is smack dang
in the middle of the pacific plate with not plate movement/destruction/yada.
Theory
The distinctive linear shape of the Hawaiian Island – Emperor Seamounts chains
resulted from the Pacific Plate moving over a deep stationary hot spot in the mantle
about 60km below the plate.
Heat from this hot spot produced a persistent source of magma, melting the
overriding Pacific Plate (due to high temperature). That area of the crust became
exceptionally thin, allowing basaltic magma, which is lighter than the surrounding
solid rock, to rise through the mantle and crust to erupt on the sea floor, forming an
active seamount. Over time, countless eruptions caused the seamount to grow and
eventually form islands.
The continuing plate movement eventually carries the island beyond the hotpot,
cutting it off from the magma source, causing volcanic activity to cease. As one
island volcano becomes extinct, another develops over the hot spot. The cycle of
growth and death left a long trail of volcanic islands and seamounts across the
Ocean floor.
The oldest volcanic rocks on Kauai, the northwestern, most inhabited Hawaiian
island, are about 5.5 million years old and are deeply eroded. In contrast, the
southeastern most island in the chain have their oldest exposed rock at less than 0.7
million years old, and new volcanic rocks are still formed. It is known as the “Big
Island” of Hawaii and it probably still positioned over the hotspot.
Volcanoes: Pros and Cons
Advantages
Environmental
-
Fertile soils
o In tropical, rainy regions, such as the windward (northeastern) side of
the Island of Hawaii, the formation of fertile soil and growth of lush
vegetation following an eruption can be as fast as a few hundred
years.
o Some of the best rice-growing regions of Indonesia are in the shadow
of active volcanoes.
o Before the great explosion of Krakatoa in 1883, for example, its region
of the island of Sumatra was relatively poor, whereas afterward it
became prosperous and heavily settled. But prosperity was delayed by
the 25 years it took to recover from the desolation immediately
following the eruption.
Social
-
Geothermal energy
o Harnessed from the Earth's natural heat
o Associated with active volcanoes or geologically young inactive
volcanoes still giving off heat at depth.
o Steam from high-temperature geothermal fluids can be used to drive
turbines and generate electrical power
o Lower temperature fluids provide hot water for space-heating
purposes, heat for greenhouses and industrial uses, and hot or warm
springs at resort spas.
 For example, geothermal heat warms more than 70 percent of
the homes in Iceland, and The Geysers geothermal field in
Northern California produces enough electricity to meet the
power demands of San Francisco. The Geysers area is the
largest geothermal development in the world.
Economical
-
Mineral Mining
o Copper, gold, silver, lead, and zinc, are associated with magmas
found deep within the roots of extinct volcanoes located above
subduction zones.
o Rising magma does not always reach the surface to erupt; instead it
may slowly cool and harden beneath the volcano to form a wide
variety of crystalline rocks
o Ore deposits commonly form around the magma bodies that feed
volcanoes because there is a ready supply of heat, which
convectively moves and circulates ore-bearing fluids.
o The metals, originally scattered in trace amounts in magma or
surrounding solid rocks, become concentrated by circulating hot fluids
and can be redeposited, under favorable temperature and pressure
conditions, to form rich mineral veins
o
-
The concentration of sand mining in the Belham Valley is a relatively
recent phenomenon resulting from the pyroclastic flows that ended
sand mining at Trant’s on the eastern side of the island in February
2010. The Belham Valley is currently the only accessible location for
sand mining, although other locations may become available in the
future be minable again once the more recent volcanic deposits cool
down). There are estimated to be several tens of millions of tonnes of
good grade resources in the Belham Valley and this is likely to increase
over time as material continues to be washed down from the slopes of
the volcano.
Tourism
o Hot springs
 Development of spas and health centres
o Volcanoes as tourist attractions
 Mt Pinatubo allows tourists to trek to the crater
o Many locals employed I the hotels, restaurants and other tourist related
services
Disadvantages
Environmental
-
-
Social
These gases form a brown fog that is caustic to most animals and plants.
o The volcanic fog has been causing major problems with farms on
Hawai’i. Since the new activity at Halemaumau Kilaeua has been
spewing much larger volumes (2-4 times more) of volcanic gases such
as sulfur dioxide, carbon dioxide, water and carbon monoxide than in
previous years.
o The sulfur dioxide, in particular, has caused many crops to fail thanks to
the production of sulfuric acid with the sulfur dioxide interacts with
water - think of it as a very concentrated version of “acid rain” that is
seen in the eastern United States.
Ejection of Greenhouse gases and other Pollutants (Mt. Pinatubo)
o 20 million tons of sulfur dioxide released
o Layer of sulfuric haze over the following months
o enormous cloud of volcanic ash that rose as high as 22 miles into the
air and grew to more than 300 miles across,
o avalanches of hot ash (pyroclastic flows) roared down the slopes of
the volcano at more than 80km/hr and filled deep valleys with deposits
of ash as much as 600 feet thick.
Climate
o Global temperatures dropped by 0.5 degrees Celsius
Landslides
-
-
-
-
-
Destruction of private properties and lives of people in 1991
Deaths
o Mt Pinatubo which released 10 million tonnes of lava and 20 million
tonnes of so2. it also caused the death of 847 locals. 250 were killed by
the collapse of roofs under the weight of wet ash.
Damaged healthcare facilities
o Encouraged the spread of diseases. (Mt. Pinatubo)
Education for thousands of children disrupted (Mt. Pinatubo)
Erosion of Culture and Traditions (Mt. Pinatubo)
o Aeta  Native tribe living near Mt Pinatubo.
o Each were relocated to govt organized settlement areas
o Each family received small plots of land not ideal for growing crops
o Found casual labour working for lowland farmers
o Fragmented Aeta society
Displacement of people
o Hundreds died in relocation camps due to poor hygiene
o Before the cataclysmic eruption, about 1,000,000 people lived in the
region around Mount Pinatubo
Landslides
o Deaaaaths
o Infrastructure is sad
Flooding (Iceland)
o Heat melted ice caps
o Meltwater subsequently emerged from the edge of the ice cap as a
glacial burst (or jokulhlaup), causing flooding. Local roads beside the
Markarfljot river were washed away and 800 local people were
evacuated because of the risk of flooding.
Economical
-
-
Flight safety
o Icelandic volcano eruption in 2012 the cloud of volcanic ash drifting
across Europe turned the continent into a no-fly zone disruption have
caused flights to be grounded longer flights to be grounded and
impacted many business with many speculating of a 1-2% drop in
European economies The most direct casualty of the ash is the airline
industry.
o The International Air Transport Association estimates that airlines are
collectively losing £130m per day in lost revenues. If the disruption
persists for several weeks, total losses could run into billions, having a
catastrophic effect on an industry already set to lose £1.4bn this year.
Geothermal energy
o a fraction of pollution caused energy stability should the steam run out
dry spells can last for years and even decades
Drilling into the crust can not only release steam but also poisonous
gases.
Ash clouds
o Covered and area of some 125000 km2, bring complete darkness to
central Luzon (Mt. Pinatubo)
Agriculture (Mt. Pinatubo)
o Destruction of Crops  800 square km of rice growing land destroyed
o 800 000 head of livestock and poultry killed
o Cost  1.5 billion pesos
o Drinking water contaminated by fluorine-tainted ash and farmers had
to keep their livestock indoors (Iceland)
o
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-
-
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About 96,200 ha of agricultural land were seriously affected by ash fall.
Damage from lahars, flooding, and siltation, as of November 17, 1992, was
reported to be 1422 million pesos.
o crops suffered the biggest damage (547 million pesos)
o fisheries (165 million pesos)
o sugarcane (57 million pesos)
o livestock (10 million pesos)
Destruction of infrastructure
http://pubs.usgs.gov/pinatubo/mercado/