Volcanoes & the stuff they doIntroductionVolcanism: Processes whereby magma and associative materials are forced into the Earth’s crush (intrusive) and/or ejected onto the Earth’s Surface (extrusive).

Instrusive

Movement of molten magma in the E’s crust Cools and solidifies within the crush Intrudes along lines of weakness Plutonic volcanism

Extrusive

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 TecPlate 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

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:

Constructiveo Mid Oceanic Ridge 15%

Spreading ridges Volcano Destructive

o Subduction zones 80% Hot spots

o Interior of plates 5%o Mostly in Hawaii

Circum Pacific (Ring of Fire)

o 2/3 of world’s volcanoes Medit Region

o Italy, Pompeiio 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 type

Characteristics Examples

Flood or Plateau Basalt

Very liquid lava, flows very widespread, emitted from fractures

Columbia River Plateau

Shield Volcano

1. Large volcano2. Gentle sloping sides3. Formed by basaltic lava with low viscosity and

higher temp4. Lava flows easily and can cover a much longer

distance before it solidifies5. 90% of the volcano is lava rather than

pyroclastic material6. Found I environments with large supply magma

like hot spots and subduction zones7. Gentle eruptions- flowing or sputtering lava.

Due to low viscous lava which do not solidify readily

Larch Mountain, Mount Sylvania, Highland Butte, Hawaiian volcanoesMauna Loa of Hawaii covers the largest area while the tallest measures from its base to peak is Mauna Kea of Hawaii (4.2km)

Cinder Cone/Scoria Cone

1. Explosive liquid lava emitted from central vent2. Large3. Cinder cones grow rapidly4. Rarely exceed 250m in height and 500m in

diameter

Famous cinder cone = Parictuin. It grew out of a corn field in

In order of increasing

violence and viscosity

Cancelled= not tested

5. Sometimes has a collapsed caldera6. Among most common volcanic landforms7. Eruptions usually don’t cause any loss of life

not famous8. Chiefly formed by Strombolian eruption

relatively low-level volcanic eruptions9. Grow up in groups 10.Occus on flanks of stratovolcanoes and

shield volcanoes11.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

Mexico in 1943 from a new vent. Within 5 days, it grew 300 feet.

Composite/Stratovolcano

1. Most common60%2. Common in Subduction Zone3. Formed by felsic lava with high viscosity. 4. Formed by alternating layers of lava and

pyroclastic material hence “composite”5. Lava solidify and pile up easily6. Tall conical structure with moderate slope7. Lava travel short distance8. Felsic Lava high in silica9. Violent eruptions of ash and pyroclast due to

viscous magmao 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 press10.Often form impressive snow capped peaks

o Exceeding 2500m in height, 1000 sq. km in surface and 400km cube in volume

11.Large conical shape12.Steep summit, gentle base13.Ash and cinder give the steepness of volcano

Mt. St. Helens (USA), Mt Pinatubo and Mt. Mayon (Philippines), Mt Fuji (Japan), Gunung Merapi (Indonesia), Mt Vesuvius

while lava cements the structure14.Very quiet between eruptions look like

extinct15.Pyroclastic flow + violent eruption = Most

hazardous to people16.Violent eruptions cause cracks to develop

secondary cones forming Parasitic cones/secondary cones/conelets

Volcanic Dome

Very viscous lava Relatively small Can be explosive Occurs adjacent to craters of composite

volcanoes (usually)

Novarupta. Mount St. Helens Lava dome, Mono craters

Caldera Very large composite volcano collapsed after an explosive period

Associated with plug domes Aka collapsed crator

Crater Lake, New berry, Kilauea, Long Valley, 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 sulfur2. Dormant ’sleeping’. Has not erupted for the past 500 million years3. 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 fine-grained 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

Readily- highly fluid- flows quietly as - 16-48km/hr

Acidic– light coloured

High High Lower- 800 degrees

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

Formation

Rocks formed from solidified

molten magma

Movement of crustal plates

built up pressure

Pressure released along

faults and fractures

Magma rises along these

lines of weaknesses

Ejected onto E’s Surface

If vent is blocked, gases within magma

expands

Drives out the magma as

lava

Lava may shatter and form ash,

cinder, dust, etc (pyroclastic material)

Volcano matter

poured outFall back near

ventAccumulation of Volcanic matter eventually build

up Volcano!

Causes of their FormationCauses of an Eruption/Formation

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 /LandformsIntrusive 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

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

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

Saucer shaped mass of igneous rocks Intrudes along bedding planes of rock strata

Sill

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)

Dyke

Mass of magma that cuts across bedding planes obliquely/vertically along joints/cracks

Few cm – hundred metres thick Few m – km long Exposed to form ridge/promontory

o More resistant rockso 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

Associated FeaturesGeysers

Hot spring which discharges jets of superheated water periodically

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.

Old Faithful Yellowstone National Park (USA)

Fumaroles

Opening in the E’s crust which emits steam and gaseso Co2, So2, HCL, HSo4

Often found near volcanoes

Lava Plateaus

Large amt of lava escapes to the surface of E from a fault line Deccan Plateau India

Craters

Large bowl of depression commonly found on the summit of volcanoes collection of rain crater lake

Caldera

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 eruptiono Removal of magma more than replenishment, causing an empty

chamber and therefore, collapsed crater

Types of Volcanic EruptionGentle Sloping Shield Volcanoes

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

Mild explosive eruptions; fumaroles Magma, incandescent bombs, ash and lapilli ejected Magma-type variable Considerable gas build up

o Stromboli (Italy), Paricutin (Mexico), Kivu (Zaire)

Stratovolcanoes

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:

Glowing avalancheo Avalanche of rock fragments mixed with hot lava accompanied by

huge clouds of dust and asho 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 volcanoo Gain more matter as it rolls down the slope o Move rapidly 1m/s – 40m/s o Consistency of cemento Triggered by E’s movemento Move along river valley

Ashflowso 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 affectedo Sound, Air, Water pollution. Destruction of Biodiversity.

Effect on climateo Could decrease the temperature as the sunlight is blockedo Sulfur particles cause losses in the ozone

Fires

Types of Materials erupted besides LavaDuring 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. Solid materials ejected during Volcanic eruptions2. Ash (<2mm)3. Lapilli (2mm – 64mm)4. 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 eruptionsa. Carbon monoxide/dioxide, sulfurous gases, nitrous gases, steam,

etc6. Lahars

a. Lava + other materials + water

Forecasting VolcanoesTiltmeters

- Monitor swells in the volcano by recording the following:o Changes in the slope angleo Swelling at the summit

Can be as little as 1m in 10 years

Earthquakes

- As new magma forces its way upwards, it releases small earthquakes

Seismographs

- As many as 1000 minor/shallow earthquakes/day can be an indication of a possible eruption

National Volcano Early Warning System

- 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 ConsAdvantagesEnvironmental

- 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 powero 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.

- Tourismo Hot springs

Development of spas and health centreso Volcanoes as tourist attractions

Mt Pinatubo allows tourists to trek to the cratero Many locals employed I the hotels, restaurants and other tourist

related services

DisadvantagesEnvironmental

- 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 releasedo Layer of sulfuric haze over the following monthso 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

Social

- 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 areaso Each family received small plots of land not ideal for growing cropso Found casual labour working for lowland farmers o Fragmented Aeta society

- Displacement of peopleo Hundreds died in relocation camps due to poor hygieneo Before the cataclysmic eruption, about 1,000,000 people lived in

the region around Mount Pinatubo- Landslides

o Deaaaathso Infrastructure is sad

- Flooding (Iceland)o Heat melted ice capso 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 safetyo 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 o 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 killedo Cost 1.5 billion pesoso Drinking water contaminated by fluorine-tainted ash and farmers

had to keep their livestock indoors (Iceland)

- 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/