Volcanoes

Question 1

Active Volcano

Answer 1

An active volcano is a volcano that has had at least one eruption during the past 10,000 years. An active volcano might be erupting or dormant.

Question 2

Composite cone volcano

Answer 2

A conical volcano built up by many layers (strata) of hardened lava, tephra, pumice, and volcanic ash. Forms at destructive subduction plate boundaries. Typical of andesitic and rhyolitic lava flows. Large heights with steep profile, slopes of 10 degrees to 30 on top. Catastrophic eruptions due to internal pressures from viscous magma. Other features: calderas, pyroclastic flows, lahars, ash clouds, volcanic bombs, e.g. Mount Fuji, Krakatoa (erupted 1883)

Question 3

Crater

Answer 3

A roughly circular depression in the ground caused by volcanic activity. It is typically a bowl-shaped feature within which occurs a vent or vents.

Question 4

Andesitic lava

Answer 4

Lava which is more viscous than basaltic lava due to higher silica content (60%) so flows at a slower rate. It has a lower temperature (800-1000 degrees Celsius) than basaltic lava. Gas content is higher than in basaltic lava (3-4%) with intermediate explosivity. Formed at converging plates where subduction occurs. E.g. Mount St. Helens (Washington state)

Question 5

Basaltic lava

Answer 5

Mafic, least viscous lava (fast and runny) due to a lower silica content (50%). It is the hottest type of lava at 1100 to 1200 degrees Celsius. Gas content is lower than in other lava types (0.5-2%) with least explosivity (low VEI). Formed at core mantle boundary when a portion of the mantle is melted and emitted at constructive boundaries or hot spots. E.g. Hawaiian Islands (Mauna Loa)

Question 6

Rhyolitic lava

Answer 6

Felsic, most viscous lava so flows at slowest rate (block flow) due to the highest silica content (70%). It has the lowest temperature (650-800 degrees Celsius). Gas content is highest (4-6%) with greatest explosivity. Formed due to melting of lithosphere and slabs of previously subducted plate. Formed at converging plates, e.g. Yellowstone volcano, USA

Question 7

Ash

Answer 7

Refers to all explosive eruption products (tephra), including particles larger than 2mm. When (dissolved) gases inside a volcano’s magma chamber expand, they violently push molten rock (magma) up and out of the volcano.

Question 8

Dormant volcano

Answer 8

A dormant volcano is an active volcano that is not erupting. A dormant volcano is one that hasn’t erupted in the past 10,000 years, but which is expected to erupt again.

Question 9

Extinct volcano

Answer 9

An extinct volcano has not had an eruption for at least 10,000 years and is not expected to erupt again in a comparable time scale of the future.

Question 10

Magma chamber

Answer 10

A magma chamber is a large underground pool of liquid rock found beneath the surface of the Earth. The molten rock in such a chamber is under great pressure, and given enough time, that pressure can gradually fracture the rock around it creating outlets for the magma.

Question 11

Parasitic Cone

Answer 11

The cone-shaped accumulation of volcanic material not part of the central vent of a volcano. It forms from fractures from eruptions on the flank of the volcano. These fractures occur because the flank of the volcano is unstable.

Question 12

Plug

Answer 12

A volcanic object created when magma hardens within a vent on an active volcano. When present, a plug can cause an extreme build-up of pressure if rising magma is trapped beneath it, and this can sometimes lead to an explosive eruption.

Question 13

Pyroclastic Flow

Answer 13

A fast-moving current of hot gas and volcanic matter (tephra), which reaches speeds moving away from a volcano of up to 700 km/h and spreading laterally under gravity. The gases can reach temperatures of about 1,000 °C. Speed depends on density of the current, volcanic output rate and gradient of slope.

Question 14

Dyke

Answer 14

A dike or dyke, in geological usage, is a sheet of rock that formed in a fracture in a pre-existing rock body. Dikes can be either magmatic or sedimentary in origin. Magmatic dikes form when magma intrudes into a crack then crystallizes as a sheet intrusion, either cutting across layers of rock or through an unlayered mass of rock. Clastic dikes are formed when sediment fills a pre-existing crack
Dykes - these are vertical intrusions with horizontal colloing crakcs. They cut across the bedding planes of the rocks into which they have been intruded. Dykes often occur in groups where they are knwon as dyke swarms. Many Scottish Islands, such as Mull and Skye have clusters of dykes all associated with one instrusive event.

Question 15

Sill

Answer 15

Sills - these are horizontal intrusions along the lines of beeding planes. Sills have vertical cooling cracks. Examples include the Great Whin Sill (which carries part of Hadrian’s Wakk) and Drumadoon on the Isle of Arran. Both sills and dykes are commonly made up of dolerite.
a sill is a tabular sheet intrusion that has intruded between older layers of sedimentary rock, beds of volcanic lava or tuff, or even along the direction of foliation in metamorphic rock. The term sill is synonymous with concordant intrusive sheet.

Question 16

Intrusive volcanic features

Answer 16

When magma is forced to the surface only a small amount of the mass actually reaches that level. Most of the magma is intruded into the crust where it solidifies into a range of features. These are often exposed at the surface by later erosion
Batholiths are formed deep below the surface when large masses of magma cool and solidify. As the magma cools slowly, large crystals are formed in the rock (e.g. granite). Batholiths are often dome-shaped and exposed by later erosion. This is the case on Dartmoor (left) and on the Isle of Arran. Batholiths can be several hundreds of kilometres in diameter. The area surrounding the batholith is altered by the heat and pressure of the intrusion to form a metamorphic aureole (limestone, for example can be transformed into marble). Batholiths are unaffected by the characteristics and structure of existing rock. Sometimes smaller injections of magma fom a lens shape that is intruded between layers of rock. This then forces the overlying strata (layers of rock) to arch upawards, forming a dome. This feature is knwon as a laccolith, and it may be exposed by later weathering and erosion to form a small range of hills, for example the Eildon Hills on the Scottish Borders.
dykes and sills
INTRUSIVE volcanic features are intruded into the lithosphere or rock, there they cool and solidify into rocks and are later exposed at the land surface as erosion and weathering DENUDE the land downwards. The majority of volcanic features are actually intrusive, most volcanic materials never actually make it to the ground surface in their molten state.

Question 17

Extrusive volcanic features

Answer 17

When volcanic activity takes place above ground, so that hot molten magma is released onto the landscape, we say that the volcanic activity is extrusive, meaning it is on the exterior, or outside of the Earth. Magma that reaches the service is known as lava. Lava flows are extraordinarily hot, and destructive.

Question 18

Geyser

Answer 18

A fountain of water and steam that builds up pressure underground and erupts at regular intervals. a hot spring in which water boils sending a tall column of water and steam into the air, formd due to hydrogeological conditions nesr ctive volcanic areas due to proximity of magma, surface water works its way down to an average depth of around 2000 metres where it contacts hot rocks, resultant boiling of pressurised water results in geyser effect of hot water and steam spraying out geyser;s surface vent, e.g. Strokkur geyser erupts every 5-8 minutes up to 30m

Question 19

Geothermal

Answer 19

of or relating to the heat in the interior of the earth

Question 20

Cloud seeding

Answer 20

A form of weather modification which attempts to change the amount of precipitation that falls from clouds by dispersing substances into the air that serve as cloud condensation or ice nuclei which alter processes in the cloud. Usually used to increase precipitation or in airports for hail and fog suppression, could be used to clear volcanic ash with water vapour clouds.

Question 21

Formation of composite volcano

Answer 21

Magma rises when water trapped in rocks of upper oceanic crust is released into mantle rock of asthernosphere above sinking oceanic slab. Mantle rock undergoes partial melting and rises due to its lower density relative to the surrrounding mantle rock. Magma rises through the curst and pools in magma chamber. Low pressure allows water and other volatiles to escape from magma as gases and as it accumulates, plug of volcanic cone is overcome leading to sudden explosive eruption. alternate layers of lava flows and pyroclastic material (50% oyrocasltci)

Question 22

Shield volcano

Answer 22

A broad domed volcano with gently sloping sides (2-3 degrees reaching 10 degrees at top), characteristic of the eruption of fluid, basaltic lava, formed at constructive plate boundaries. Smaller heights with low profile. Features: rift zones, cinder cones, lava tubes, plateaus, calderas, e.g. Mauna Loa

Question 23

Formation of shield volcano

Answer 23

Build of fluid magma flows, steady accumulation of broad sheets of lava and thin sheets (less than 1m thick), They are the product of gentle effusive eruptions with high magma supply rates. common product of hotspot volcanism, 90% is lava rather than yroclastici material;

Question 24

Caldera

Answer 24

a large volcanic crater, especially one formed by a major eruption leading to the collapse of the mouth of the volcano.

Question 25

Tephra

Answer 25

pieces of volcanic rock and ash that blast into the air after a volcanic eruption. larger pieces fall near the volcano, causing injury or death and destruction to structures, smaller pices can travel for thousands of kilometres, ash fall acauses poor visibility and slippery roads and roofs can fall under the weight and clog engines (disrupt air travel)

Question 26

Lahar

Answer 26

type of mudlow composed of slurry pyroclastic material, rocky debris and warer which flows from a volcano along a river valley with consistency and approximate density of wet concrete, destrucitve, can flow tens of metres per second over 22mph and 140m deep, e.g. lahar at Nevado del Ruiz, Colombia which killed over 23,000 people 1985

Question 27

Jökulhlaup

Answer 27

a type of glacial outburst flood due to heat from a volcanic eruption melting the snow and ice in a glacier, large amounts of water, rock, gravel and ice can suddenly be released catching people unaware and damaging land and infrastructure. occur anywhere where water accumulates in a subglacial lake beneath a glacier

Question 28

Hot spot

Answer 28

A hot spot is is fed by a region deep within the Earth’s mantle from which heat rises through the process of convection. This heat facilitates the melting of rock at the base of the lithosphere, where the brittle, upper portion of the mantle meets the Earth’s crust. The melted rock, known as magma, often pushes through cracks in the crust to form volcanoes.

Hot spot volcanism is unique because it does not occur at the boundaries of Earth’s tectonic plates, where all other volcanism occurs. Instead it occurs at abnormally hot centers known as mantle plumes. Scientific models depict these plumes of molten rock almost like a lava lamp, with a rising bulbous head fed by a long, narrow tail that originates in the mantle. As the plume head reaches the lithosphere, it spreads into a mushroom shape that reaches roughly 500 to 1000 kilometers (310 to 621 miles) in diameter. These features are called diapirs.

Scientists have different theories about where hot spots form. The dominant theory, framed by Canadian geophysicist J. Tuzo Wilson in 1963, states that hot spot volcanoes are created by exceptionally hot areas fixed deep below the Earth’s mantle. More recent scientific studies suggest that these hot spots may be found at more shallow depths in the Earth’s mantle and may migrate slowly over geologic time rather than stay fixed in the same spot.

A volcano above a hot spot does not erupt forever. Attached to the tectonic plate below, the volcano moves and is eventually cut off from the hot spot. Without any source of heat, the volcano becomes extinct and cools. This cooling causes the rock of the volcano and the tectonic plate to become more dense. Over time, the dense rock sinks and erodes. A new and active volcano develops over the hot spot, creating a continuous cycle of volcanism.

Hot Spot Features

Most scientists think that 40 to 50 hot spots exist around the world, although this number varies widely because of differing definitions of what a hot spot is. Major hot spots include the Iceland hot spot, under the island of Iceland in the North Atlantic; the Réunion hot spot, under the island of Réunion in the Indian Ocean; and the Afar hot spot, located under northeastern Ethiopia.

Volcanic activity at hot spots can create submarine mountains known as seamounts. Some scientists estimate that seamounts make up 28.8 million square kilometers (17.9 million square miles) of the Earth’s surface, an area larger than any other habitat. Depending on the amount of volcanic activity, seamounts can rise hundreds or thousands of meters from the seafloor.

The Louisville Seamount Chain, for example, is comprised of over 80 seamounts that extend in a 4,000 kilometer (2,485 mile) arc in the South Pacific Ocean, about 1,500 kilometers (932 miles) from Wellington, New Zealand. The seamounts originated from a single hot spot and have been slowly transported in a northwest direction by the Pacific plate.

Hot spot seamounts that reach the surface of the water can create entire chains of islands, such as the U.S. state of Hawaii. Scientists think that this volcanic chain of islands has been forming for at least 70 million years over a hot spot underneath the Pacific plate. The Hawaiian Islands were created one right after the other as the plate moved northwest—almost like an island factory. Of all the inhabited Hawaiian Islands, Kauai is located farthest from the presumed hot spot and has the most eroded and oldest volcanic rocks, dated to be around 5.5 million years old. Meanwhile, on the “Big Island” of Hawaii, the oldest rocks are less than 0.7 million years old and volcanic activity continues to create new land.

Hot spots can also develop beneath continents. The Yellowstone hot spot, for example, has produced a series of volcanic features that extend in a northeastern direction. The features stretch from the U.S. states of Idaho and Oregon, some 650 kilometers (400 miles) to northwest Wyoming. Over 16.5 million years, the hot spot has generated 15 to 20 massive eruptions that left large volcanic depressions called calderas. The McDermitt Volcanic Field, located on the Nevada-Oregon border, is the hot spot’s oldest large feature. It formed from an eruption roughly 16.1 million years ago. The active Yellowstone Caldera, in Yellowstone National Park in northwest Wyoming, is the hot spot’s youngest large feature, having last erupted just 640,000 years ago.

Hot spots don’t always create volcanoes that spew rivers of lava. Sometimes, the magma heats up groundwater under the Earth’s surface, which causes water and steam to erupt like a volcano. These eruptions are called geysers. A famous geyser is Old Faithful in Yellowstone National Park. When it erupts, the water is 95.6 degrees Celsius (204 degrees Fahrenheit) and can reach more than 55 meters (180 feet) high.

Question 29

Mantle plume

Answer 29

upwelling of magma within Earth’s mantle
A mantle plume is posited to exist where hot rock nucleates at the core-mantle boundary and rises through the Earth’s mantle becoming a diapir in the Earth’s crust.[3] The currently active volcanic centers are known as “hot spots”. In particular, the concept that mantle plumes are fixed relative to one another, and anchored at the core-mantle boundary, was thought to provide a natural explanation for the time-progressive chains of older volcanoes seen extending out from some such hot spots, such as the Hawaiian–Emperor seamount chain.

Question 30

Slab pull

Answer 30

Slab pull is the pulling force exerted by a cold, dense oceanic plate plunging into the mantle due to its own weight. The theory is that because the oceanic plate is denser than the hotter mantle beneath it, this contrast in density causes the plate to sink into the mantle. The process of a tectonic plate descending into the mantle is termed subduction.

Question 31

Subduction zone

Answer 31

the process by which collision of the earth’s crustal plates results in one plate’s being drawn down or overridden by another, localized along the juncture (subduction zone) of two plates SEE ASSESSMENT

Question 32

Subduction zone

Answer 32

the process by which collision of the earth’s crustal plates results in one plate’s being drawn down or overridden by another, localized along the juncture (subduction zone) of two plates SEE ASSESSMENT
Wouter Schellart developed a global map showing subduction zones and found the main indicators include style of deformation in the plate overlying the subduction zone, leve l of stress, dip angle, curvature as well as rate of movement, to predict which ones are capable of giant earthquakes

Question 33

Viscosity

Answer 33

Viscosity is a measure of a fluid’s resistance to flow. It describes the internal friction of a moving fluid. A fluidwith large viscosity resists motion because its molecular makeup gives it a lot of internal friction. A fluid with low viscosity flows easily because its molecular makeup results in very little friction when it is in motion.