Chapter 11- Volcanism (Week 4) Flashcards
(152 cards)
1
Q
What is a volcano?
A
A volcano is a location where molten rock flows out, or erupts, onto Earth’s surface as lava. Volcanic eruptions can happen on land or underwater.
2
Q
What are fissure eruptions?
A
Fissure eruptions are volcanic eruptions flowing from long cracks in the Earth.
3
Q
What are the main parts of a volcano?
A
The main parts of a volcano include a magma chamber, vent or conduit, crater, and the possibility of a flank eruption.
*image 1
4
Q
Describe the process when volcanoes erupt.
A
During an eruption, magma moves upward from a magma chamber through a vent or conduit. It then flows out from a crater at the top or, in some cases, emerges at a secondary site on the side, resulting in a flank eruption. The erupted materials accumulate around the vent, forming a volcanic mountain.
The accumulated material might consist of layers of solidified lava, called lava flows, but it might also include fragments of various sizes that have been thrown from the volcano.
5
Q
What is the difference between a crater and a caldera?
A
A crater is a basin above a volcano’s vent with diameters on the scale of 10s to 100s of meters. A caldera is a larger, bowl-shaped structure (km in scale) that forms when a volcano collapses in on itself after an eruption, leaving a broad basin rimmed by the remnants of the volcano.
6
Q
Describe the process of caldera formation.
A
Calderas form when a volcano’s magma chamber is drained during an eruption, leading to a loss of support for the volcano. The unsupported part collapses into the void in the magma chamber, creating a broad basin. Over time, the basin can fill with water. If there is still magma activity, the caldera floor may be lifted, or a new volcano may form within the caldera. The island of Santorini is an example of a caldera, formed after an enormous eruption around 1627-1600 BCE.
*image 2
7
Q
What are the main parts of a volcano?
A
The main parts of a volcano include the magma chamber, vent or conduit, crater, and accumulated materials like lava flows and fragments around the vent forming a volcanic mountain.
8
Q
How do fissure eruptions differ from those flowing from mountains?
A
Fissure eruptions flow from long cracks in the Earth, while eruptions from mountains typically involve magma moving upward from a magma chamber through a vent or conduit, flowing out from a crater at the top or sometimes emerging at a secondary site on the side of the volcano, resulting in a flank eruption
9
Q
What are the three main types of materials produced by volcanic eruptions?
A
Volcanic eruptions produce three types of materials: gas, lava, and fragmented debris known as tephra.
10
Q
Describe the process of gas release during a volcanic eruption.
A
Magma contains dissolved gases under high pressure. When the pressure decreases, these gases come out of solution, forming bubbles. The primary components of volcanic gas emissions are water vapor, carbon dioxide (CO2), sulfur dioxide (SO2), and hydrogen sulfide (H2S). Volcanoes release gases during eruptions, through openings called fumaroles, and into soil and groundwater.
his process is analogous to what happens when a pop bottle is opened. Pop is bottled under pressure, forcing carbon dioxide gas to dissolve into the fluid. As a result, a bottle of pop that you find on the supermarket shelf will have few to no bubbles. If you open the bottle, you decrease the pressure within it. The pop will begin to fizz as carbon dioxide gas comes out of solution and forms bubbles
*image 3
11
Q
What factors influence the ease with which lava flows and the structures it forms?
A
The ease with which lava flows and the structures it forms depend on the lava’s silica content and the presence of gas. Higher silica content leads to increased polymerization, making the lava stiffer. The stiffness, or viscosity, of lava is a key factor—low-viscosity lava flows easily, while high-viscosity lava is sticky and stiff.
12
Q
How does the silica content of lava relate to its gas content?
A
In general, high-silica lava contains more gas than low-silica lava. The gas, when forming bubbles, further increases the viscosity of the lava.
Consider the pop analogy again. If you were to shake the bottle vigorously and then open it, the pop would come gushing out in a thick, frothy flow. In contrast, if you took care to not shake the bottle before opening it, you could pour out a thin stream of fluid.
13
Q
What factors influence the thickness and shape of a lava flow?
A
The viscosity of the lava is a crucial factor. Higher viscosity results in thicker flows, and the lava solidifies at a shorter distance. Highly viscous lava might not flow very far at all, may accumulate as a bulge, known as a lava dome, within a volcano’s crater.
*image 5
14
Q
How does the viscosity of lava affect its flow distance?
A
Lower viscosity, as seen in less viscous rhyolitic lava, allows for longer travel distances. In contrast, highly viscous lava, like basaltic lava, can flow as thin streams.
*image 6
15
Q
How do lava tubes form, and what is their significance in volcanic activity?
A
Lava tubes form naturally as flowing mafic lava cools near its margins, creating solid lava levées. Over time, these levées close over the top of the flow, forming tubes. Lava tubes can extend for long distances, insulating the lava from the atmosphere and allowing it to flow for tens of kilometers. They are significant features in volcanic activity, contributing to extended lava flow distances.
*image 7
16
Q
What is pahoehoe lava, and how does it develop a wrinkled texture known as ropy lava?
A
Pahoehoe is basaltic lava with an unfragmented surface. It can be smooth and billowy, developing a wrinkled texture called ropy lava. Ropy lava forms when the outermost layer of the lava cools and develops a skin, which is still hot and flexible. As the lava flows, the skin is dragged and folded into wrinkles, creating a distinctive texture.
*image 8
17
Q
What is a’a lava, and how does its texture differ from pahoehoe lava?
A
A’a (pronounced like “lava” without the “l” and “v”) is a type of basaltic lava with a sharp and splintery, rubble-like texture. Unlike pahoehoe lava, a’a lava is characterized by a broken and fragmentary outer layer. This texture results when the outer layer of the lava flow breaks into fragments as the lava moves beneath it, creating a rough and blocky surface.
*image 9
18
Q
What is blocky lava, and how does it differ from a’a lava?
A
Blocky lava is a type of lava with a fragmented surface, and it is typically associated with higher viscosity lavas, such as andesitic lava. Unlike a’a lava, blocky lava has fragments with smoother surfaces and fewer vesicles. The surface of blocky lava is rough and block-like due to the breaking of the outer layer into fragments as the lava moves beneath it.
*image 6
19
Q
How do lava pillows form, and what information can they provide about the past environment?
A
Lava pillows form when lava flows into water, causing the outside of the lava to cool quickly, creating a tube. Blobs of lava develop at the end of the tube, forming distinctive rounded shapes known as pillows. The presence of lava pillows in the rock record indicates that the environment at the time of lava emplacement was underwater.
*image
20
Q
What causes the formation of columnar joints in lava flows, and how do they appear?
A
Columnar joints in lava flows are formed as the lava cools and solidifies, causing shrinkage. Long vertical cracks or joints develop within the brittle rock, forming polygonal shapes when viewed from above. These polygons typically have 5, 6, or 7 sides, with angles of approximately 120 degrees between sides.
*image 11
21
Q
What term is used to collectively refer to loose material thrown from a volcano, and what are individual fragments called?
A
Loose material thrown from a volcano is collectively referred to as tephra, and individual fragments are called pyroclasts.
22
Q
What are particles less than 2 mm in diameter called, and what do they consist of in volcanic ash?
A
Particles less than 2 mm in diameter are called volcanic ash, and they consist of small mineral grains and glass.
23
Q
What are fragments with dimensions between 2 mm and 64 mm called?
A
Fragments with dimensions between 2 mm and 64 mm are called lapilli.
Pele’s tears form when droplets of lava cool quickly as they are flung through the air. Rapidly moving through the air may draw the Pele’s tears out into long threads called Pele’s hair
*image 12
24
Q
What are fragments larger than 64 mm classified as, and how do they differ based on their origin?
A
Fragments larger than 64 mm are classified as blocks or bombs, depending on their origin. Blocks are solid fragments of the volcano that form when an explosive eruption shatters the pre-existing rocks.
Bombs form when lava is thrown from the volcano and cools as it travels through the air. Traveling through the air may cause the lava to take on a streamlined shape
*image 14
25
How does the presence of gas in erupting lava affect lapilli and bombs?
The presence of gas in erupting lava can cause lapilli and bombs to take on distinctive forms as the lava freezes around the gas bubbles, giving the rocks a vesicular (hole-filled) texture. Pumice is an example, forming from gas-filled felsic lava. The mafic counterpart to pumice is scoria, and mafic lava can also form reticulite, a rare and fragile rock with a delicate network of glass due to burst bubbles.
*image 15
26
What are the products of volcanism that build volcanoes and leave lasting marks on the landscape?
The products include lava flows of varying viscosity and gas content, as well as tephra ranging in size from less than a mm to blocks with masses of many tonnes.
27
How do individual volcanoes vary in terms of volcanic materials, and what impact does this have?
Individual volcanoes vary in the volcanic materials they produce, affecting the size, shape, and structure of the volcano.
28
What are the three main types of volcanoes?
The three types of volcanoes are cinder cones (spatter cones), composite volcanoes (stratovolcanoes), and shield volcanoes.
*image 16
29
What is the characteristic shape of shield volcanoes, and why are they named as such?
Shield volcanoes have a broad, rounded shape, and they are named for this distinctive shield-like appearance.
30
Which is the largest type of volcano on Earth, and can you provide an example?
Shield volcanoes are the largest, and an example is Mauna Loa, which is the largest volcano on Earth.
Mauna Loa has a diameter of nearly 200 km and is located on the Island of Hawai‘i.
31
What type of volcano is Kīlauea, and how does it differ from Mauna Loa?
Kīlauea is a shield volcano, but it is much flatter than Mauna Loa, rising only 18 m above the surrounding terrain
32
What is the characteristic shape of composite volcanoes, and how does it differ from shield volcanoes?
Composite volcanoes have a distinctly conical shape with steep sides that tend to steepen toward the summit, unlike the broad, rounded shape of shield volcanoes.
Mt. St. Helens is a composite volcano located in the Cascade Range of the western United States.
Composite volcanoes tend to be no more than 10 km in diameter.
33
Describe the characteristics of cinder cones and provide an example.
Cinder cones are the smallest type of volcano with straight sides. An example is Eve Cone on the flanks of Mt. Edziza in northwestern British Columbia
34
How do cinder cones differ in shape from composite and shield volcanoes?
Cinder cones have straight sides, unlike the upward-steepening composite volcanoes or the rounded shield volcanoes.
35
How do shield volcanoes, such as the Sierra Negra volcano in the Galápagos Islands, acquire their gentle hill-like shape?
Shield volcanoes get their gentle hill-like shape because they are built of successive flows of low-viscosity basaltic lava.
36
What is the key factor contributing to the larger size of shield volcanoes compared to composite volcanoes or cinder cones?
The low viscosity of the basaltic lava in shield volcanoes allows it to flow for long distances, resulting in their greater size compared to composite volcanoes or cinder cones.
37
What are composite volcanoes, and what is an alternative name for them?
Composite volcanoes consist of layers of lava alternating with layers of tephra (blocks, bombs, lapilli, and ash). An alternative name for them is stratovolcanoes.
38
What is the defining feature of the structure of composite volcanoes?
Composite volcanoes have layers (strata) of lava alternating with layers of tephra, which gives them the alternative name "stratovolcanoes."
39
How does the characteristic shape of composite volcanoes, such as Cotopaxi, differ from shield volcanoes?
Composite volcanoes have slopes that get steeper near the top, reflecting the accumulation of tephra fragments near the volcano's vent.
40
What type of lavas do composite volcanoes typically erupt, and how does this affect their diameter?
Composite volcanoes typically erupt higher viscosity andesitic and rhyolitic lavas, resulting in smaller diameters compared to shield volcanoes.
41
What is a notable exception to the typical lava composition of composite volcanoes, and where is it located?
Mt. Fuji in Japan is a notable exception as it erupts basaltic lava, which is typically associated with shield volcanoes.
42
What is the geological perspective on the formation and durability of composite volcanoes?
From a geological perspective, composite volcanoes tend to form relatively quickly and do not last very long. If volcanic activity ceases, they might erode away within a few tens of thousands of years.
43
What factor contributes to the relatively short lifespan of composite volcanoes?
The presence of pyroclastic eruptive material, which is not strong, contributes to the relatively short lifespan of composite volcanoes.
44
What are cinder cones, and what is an alternative name for them?
Cinder cones, also known as spatter cones, are volcanic formations with straight sides, typically less than 200 m high.
*image 19
45
What is the main composition of most cinder cones, and how are they formed?
Most cinder cones are made up of fragments of scoria, which is vesicular rock from basaltic lava. They are formed as gas-rich magma erupts, expelling these fragments.
Cinder cones are typically less than 200 m high.
46
What is the primary reason for the relatively short lifespan of cinder cones?
Cinder cones are made up almost exclusively of loose fragments, particularly scoria, which lack strength. This makes them susceptible to easy erosion, leading to a relatively quick disappearance.
47
What determines the explosiveness of a volcanic eruption?
The explosiveness of a volcanic eruption is determined in part by the composition of magma and the amount of gas it contains. Magmas with more silica erupt more explosively.
48
How is the height of a volcanic eruption column related to its explosiveness?
The height of a volcanic eruption column is related to its explosiveness. The greater the explosiveness, the higher the eruption column, which is how high the volcano blasts material into the air.
49
What role does silica play in the explosiveness of a volcanic eruption?
Silica content in magma is crucial for explosiveness. Magmas with higher silica content have greater viscosity, allowing more pressure to build up before eruption. More silica also means more explosiveness.
50
What are the four types of volcanic eruptions based on increasing explosiveness?
The four types of volcanic eruptions, in order of increasing explosiveness, are Hawai'ian, Strombolian, Vulcanian, and Plinian eruptions.
There are four types of eruptions with properties determined mostly by the silica content of magma, and the amount of gas it contains
51
What is a hydrovolcanic eruption, and when does it occur?
A hydrovolcanic (or phreatic) eruption occurs when any composition of magma suddenly encounters water. Hot magma contacting groundwater or seawater causes the water to flash to steam, resulting in explosive eruptions.
52
What characterizes Hawai‘ian eruptions?
Hawai‘ian eruptions are effusive (flowing) rather than explosive. They are characterized by the eruption of low-viscosity basaltic lava, forming shield volcanoes or fissure eruptions.
53
What type of lava is typically erupted during Hawai‘ian eruptions?
Hawai‘ian eruptions typically involve the eruption of low-viscosity basaltic lava, contributing to their effusive and flowing nature.
*image 20
54
What is a fissure eruption, and how does it differ from eruptions with a central vent?
Fissure eruptions occur when lava erupts from long cracks in the ground rather than from a central vent. This is in contrast to eruptions that occur from a single central vent.
55
Provide an example of a Hawai‘ian eruption.
An example of a Hawai‘ian eruption is the November 1959 eruption of Kīlauea Iki Crater, which included fissure eruptions and effusive flows of lava.
56
How can Hawai‘ian eruptions, considered "gentle," still pose risks?
While Hawai‘ian eruptions are often considered "gentle," this term is relative. They range from lava flows that can be safely sampled by trained personnel to lava fountains that soar hundreds of meters above tree tops, raining large and dangerous rocks upon the surroundings.
57
What characterizes Strombolian eruptions?
Strombolian eruptions are named for Mt. Stromboli in Italy and occur when basaltic lava has higher viscosity and higher gas content. They are characterized by loud, violent, but short-lived spattery eruptions.
*image 21
58
What type of lava is involved in Strombolian eruptions, and how does it behave?
Strombolian eruptions involve basaltic lava with higher viscosity. The sticky lava is ejected in spattery eruptions, producing clumps of gas-rich lava thrown 10s to 100s of meters in the air.
59
What geological features are associated with Strombolian eruptions?
Clumps of gas-rich lava thrown during Strombolian eruptions accumulate around the vent as scoria, forming cinder cones. These cones are the result of the accumulation of ejected material.
60
Provide an example of a location associated with Strombolian eruptions.
Strombolian eruptions are named after Mt. Stromboli in Italy. Image 21 shows a strombolian eruption in the crater of Mt. Etna, where a smaller cinder cone is forming around the vent as lava sputters out.
61
What is the origin of the name "Vulcanian eruptions"?
Vulcanian eruptions get their name from the volcanic Italian island of Vulcano, which is named after the Roman god of fire, Vulcan. In Roman mythology, Vulcan was associated with volcanic activity.
62
How do Vulcanian eruptions differ from Strombolian eruptions in terms of explosiveness?
Vulcanian eruptions are far more explosive than Strombolian eruptions. They can blast tephra and gas to a height of 5 to 10 km.
*image 22
63
What is the cause of the increased explosiveness in Vulcanian eruptions?
The increased explosiveness in Vulcanian eruptions is related to a build-up of pressure. The higher viscosity of intermediate silica content lava restricts the escape of gas, leading to more explosive eruptions.
64
What types of volcanic materials are produced during Vulcanian eruptions?
Vulcanian eruptions produce large quantities of ash, in addition to blocks and bombs. The combination of these materials contributes to the explosive nature of the eruption.
65
Provide an example of a historical Vulcanian eruption and its consequences.
The Vulcanian eruption of Mt. Pelée on the island of Martinique in 1902 resulted in a devastating phenomenon known as a pyroclastic flow. The flow raced down the mountain, over the city of St. Pierre, and into the harbor, causing significant destruction and fatalities.
Scott's account vividly describes of the speed of the pyroclastic flow. In some cases, pyroclastic flows travel at speeds greater than 700 km/h. They are able to travel rapidly because they behave like a fluid, and can also ride on a cushion of hot gas
66
What are pyroclastic flows?
Pyroclastic flows are fast-moving, high-temperature mixtures of volcanic gases, ash, and fragmented rock that travel down the slopes of a volcano during an explosive eruption.
67
What characterizes Plinian eruptions?
Plinian eruptions are explosive eruptions involving intermediate to felsic lava, and they can form eruptive columns reaching up to 45 km in height.
*image 23
68
How did Plinian eruptions get their name?
Plinian eruptions are named after the eruption of Vesuvius in 79 CE, which buried the towns of Pompeii and Herculaneum. The name originates from the Roman admiral Gaius Plinius Secundus, also known as Pliny the Elder, who attempted a rescue mission during the eruption but died before reaching Herculaneum.
69
Provide an example of a more recent Plinian eruption and its consequences.
A more recent Plinian eruption occurred on April 21, 1990, at Mt. Redoubt. Pyroclastic flows and lahars (landslides caused by melted glaciers turning volcanic ash into mud) resulted from this eruption.
70
What is the significance of the eruptive column's shape in Plinian eruptions?
The shape of the eruptive column in Plinian eruptions, with parts appearing to spread out in flat layers at different levels, reflects differences in atmospheric characteristics during the eruption.
71
What characterizes hydrovolcanic (phreatic) eruptions, and how do they differ from Plinian eruptions?
Hydrovolcanic eruptions, also known as phreatic eruptions, can be far more explosive than Plinian eruptions. They occur when water, in the form of groundwater, seawater, or melting glacial ice or snow, comes into contact with magma. The sudden conversion of water to steam, expanding over a thousand times its original volume, results in an explosive force that can blast a volcano apart, creating large amounts of volcanic ash.
72
Provide an example of a hydrovolcanic eruption and its consequences.
In April 2010, the Icelandic volcano Eyjafjallajökull experienced a hydrovolcanic eruption. The melting of the glacier above the volcano released large quantities of water, triggering an explosive eruption. The resulting ash plume reached 10 km high, affecting air travel over Europe and leading to a 5-day prohibition on flights due to the potential damage volcanic ash can cause to aircraft engines.
73
How can the characteristics of volcanoes, including the types of volcanic mountains, materials produced, and eruption styles, be tied together into a big picture?
The characteristics of volcanoes can be connected by considering the plate tectonic settings in which magma forms. The majority of volcanoes are located along plate tectonic boundaries.
74
What are the four main plate tectonic scenarios related to volcanic activity?
There are four main plate tectonic scenarios:
1. Divergent boundaries, where melting is triggered by decompression.
2. Subduction zones (ocean-ocean and ocean-continent convergent boundaries), where flux melting occurs as water is released from subducting ocean crust.
3. Hot spots, where plumes of hot mantle material rise up and melt due to decompression.
4. Melting by conduction, when magma transfers heat to rocks having a lower melting temperature.
*image 25
75
What is the role of decompression in causing volcanism along ocean spreading ridges?
At an ocean spreading ridge, convection moves hot mantle rock slowly upward, leading to decompression at roughly 60 km below the surface. This decompression permits partial melting of approximately 10% of the ultramafic rock, resulting in the production of mafic magma
76
What type of magma is produced through the decompression process along ocean spreading ridges?
The decompression process at ocean spreading ridges produces mafic magma, which moves up toward the surface and fills vertical fractures produced by the spreading, resulting in the formation of pillow lavas and lava flows on the sea floor.
77
Where does spreading-ridge volcanism take place, and can you provide an example?
Spreading-ridge volcanism takes place approximately 200 km offshore from the west coast of Vancouver Island.
78
How does decompression cause volcanism in continental rift zones, and what types of volcanoes can result?
In continental rift zones where continental crust is thinning, decompression triggers partial melting of ultramafic mantle rocks. Depending on the composition of the melt and the involvement of other rocks, continental rift zones can have a range of volcano types, including shield volcanoes, broad lava flows, cinder cones, and composite volcanoes.
79
What happens at an ocean-continent convergent boundary or ocean-ocean convergent boundary in terms of subduction?
At these convergent boundaries, oceanic crust is pushed down into the mantle, but high pressures prevent the slab from melting.
80
How does water play a role in triggering partial melting along subduction zones?
Minerals in the subducted slab release water, which lowers the melting point of the rock above the slab. This water-induced partial melting occurs within the mantle.
81
What type of magma is produced in subduction zones, and what is its composition?
Mafic magma rises through the mantle to the base of the crust in subduction zones. It contributes to partial melting of crustal rock, resulting in intermediate composition magma.
82
What happens to the magma as it rises through the crust in subduction zones?
The intermediate composition magma continues to rise, assimilating crustal material. In the upper part of the crust, it accumulates into plutons, and over time, fractional crystallization within the pluton can make the magma even more silica-rich.
83
What types of volcanic eruptions are characteristic of volcanic arcs in subduction zones, and what volcanic landforms may result?
Composite volcanoes with Vulcanian or Plinian eruption styles are characteristic of volcanic arcs in subduction zones. In the Trans-Mexico Volcanic Belt, Strombolian eruptions produce short-lived cinder cones. In cases where two margins of oceanic crust collide, the volcanic arc may form a chain of volcanic islands. In collisions between continental and oceanic crust, a volcanic arc develops on the continental crust.
84
When did the significant eruption of Mt. St. Helens in 1980 occur, and what were its characteristics?
The significant eruption of Mt. St. Helens occurred on May 18, 1980, marked by a M5.1 earthquake and a 9-hour Plinian eruption. It had a 24 km high eruption column and multiple pyroclastic flows, resulting in a large portion of the volcano being blasted away.
85
What type of magma drove the explosive eruption of Mt. St. Helens in 1980, and what is the composition of this magma?
The explosive eruption of Mt. St. Helens in 1980 was driven by gas-rich rhyolitic magma. This type of magma is felsic in composition.
86
Has Mt. St. Helens only erupted felsic or intermediate materials?
No, Mt. St. Helens has erupted basaltic lava at certain times, as evidenced by the lava tube
The iMUSH project shows the presence of a magma chamber beneath Mt. St. Helens at depths between 5 and 14 km, and a much larger magma chamber extending down to the mantle.
Earthquakes in the 24 hours after the 1980 eruption (yellow arrows in image 26) suggest movement of magma within the smaller chamber. However, earthquakes from 1980 to 2005 indicate movement of magma within the deeper chamber as well (black arrows).
87
What could explain the complex volcanic history of Mt. St. Helens, including changes in magma composition?
The complex history of Mt. St. Helens may reflect changes in the composition of magma within the small chamber over time as fractionation proceeds, and the magma becomes more silica-rich. Additionally, movement of more mafic magma from the larger chamber could contribute to eruptions with different chemical compositions.
The larger magma chamber beneath Mt. St. Helens may be connected to a chamber feeding the nearby Indian Heaven Volcanic Field, which contains shield volcanoes and cinder cones, with basalt making up 80% of erupted materials.
88
What are mantle plumes?
Mantle plumes are rising columns of hot solid rock that may be kilometers to tens of kilometers across. Near the surface, they spread out to create a mushroom-like head that is tens to over 100 kilometers across.
89
How do mantle plumes differ from normal mantle convection beneath ocean spreading centers?
Mantle plumes rise approximately 10 times faster than normal mantle convection beneath ocean spreading centers. They may originate deep in the mantle, possibly just above the core-mantle boundary.
90
What happens when a mantle plume rises to the base of the lithosphere?
When a mantle plume rises to the base of the lithosphere, the low pressure permits partial melting of the plume material, producing mafic magma. The heat carried by the mantle plume can also melt rock adjacent to the plume.
91
How do hotspot volcanoes form in relation to mantle plumes?
The rising magma from the mantle plume feeds hotspot volcanoes. As the lithospheric plate moves across the plume, a chain of hotspot volcanoes can form. Existing hotspot volcanoes are slowly moved away from the mantle plume, and new ones may form in the lithosphere.
92
Give an example of a region associated with mantle plumes and the type of volcanoes found there.
Many shield volcanoes, including those in the Hawai'ian islands, are associated with mantle plumes. The Hawai'ian volcanoes, such as Mauna Loa, Kilauea, and L$"ihi, are related to the mantle plume beneath them.
93
What evidence supports the presence of mantle plumes beneath the Hawai'ian islands?
There is evidence of crustal magma chambers beneath active Hawai'ian volcanoes. For example, at K!lauea, the magma chamber appears to be several kilometers in diameter and is situated between 8 km and 11 km below the surface.
94
What are Large Igneous Provinces (LIPs)?
Large Igneous Provinces (LIPs) are regions where massive volumes of magma are produced over relatively short time periods. They are thought to be associated with high-volume but short-duration bursts of magma from mantle plumes.
95
How does the Hawaii mantle plume differ from other mantle plumes in terms of magma production?
The Hawaii mantle plume has produced a relatively low volume of magma consistently for approximately 85 million years. In contrast, other mantle plumes can generate massive volumes of magma over relatively short time periods.
96
Provide an example of a Large Igneous Province (LIP) and its characteristics.
An example of an LIP is the Columbia River Basalt Group, which covers Washington, Oregon, and Idaho in the United States. This LIP, with basaltic rock up to several hundred meters thick, erupted between 17 and 14 million years ago.
The mantle plume assumed to be responsible for the Columbia River LIP is now situated beneath the Yellowstone area, leading to felsic volcanism.
*image 28
97
What is the assumed origin of Large Igneous Provinces (LIPs), and what might be responsible for the volcanism leading to LIPs?
The origin of LIPs is still controversial, but it is thought that the volcanism leading to LIPs is related to very high-volume but relatively short-duration bursts of magma from mantle plumes.
98
What are Kimberlite pipes?
Kimberlite pipes are carrot-shaped cones of ultramafic rock formed from the explosive eruption of mantle plumes originating at depths of 150 to 450 km in the mantle.
99
How quickly do mantle plumes associated with Kimberlite eruptions make their way to the surface?
Mantle plumes associated with Kimberlite eruptions make their way to the surface quickly, over hours to days, having little interaction with the surrounding rocks.
100
Why do Kimberlite eruptions leave circular holes in the ground instead of forming volcanic mountains on the surface?
Kimberlite eruptions are highly explosive, causing circular holes in the ground rather than forming volcanic mountains on the surface.
*image 29
101
What causes the explosiveness of Kimberlite eruptions as they near the surface?
A build-up of gas near the surface causes Kimberlite eruptions to become explosive. By the time the plume reaches the surface, it may be traveling faster than the speed of sound.
102
At what depths do Kimberlite eruptions that bring diamond-bearing material to the surface typically originate?
Kimberlite eruptions that bring diamond-bearing material to the surface typically originate at depths greater than 200 km beneath old, thick, continental crust.
103
Where are diamond mines in Kimberlites commonly found, and why are they easy to spot?
Diamond mines in Kimberlites, such as the Ekati Mine in the Northwest Territories, are commonly found, and they are easy to spot due to the characteristic circular hole that develops as miners excavate the cone-shaped structure.
Kimberlites can be quite old, and the youngest known Kimberlites, such as those in the Igwisi Hills in Tanzania, are only about 10,000 years old. The next youngest date to approximately 30 million years ago.
104
What volcanic hazard on the island of Hawai'i is responsible for extensive damage to homes, infrastructure, and habitats?
Basaltic lava flows produced by volcanoes on the island of Hawai'i are responsible for extensive damage to homes, infrastructure, and habitats.
105
Why are lava flows not considered the volcanic hazard with the greatest impact on lives and infrastructure?
Lava flows, even the relatively free-flowing Hawai'ian basaltic lava, move slowly enough that they can be escaped on foot. More dangerous hazards are related to gases and volcanic debris.
106
What hazards are considered more dangerous than lava flows, and why?
Gases and volcanic debris are considered more dangerous than lava flows because they can pose immediate threats to life and health, making them more challenging to escape.
107
What is the largest impact and the greatest cause of suffering related to volcanic hazards?
The largest impact and the greatest cause of suffering related to volcanic hazards are not the immediate effects of volcanic eruptions but large-scale changes to climate and environments caused by volcanism.
Approximately 8 million deaths during historical times are attributed to indirect effects of volcanic eruptions, including respiratory distress, toxicity, famine, and habitat destruction.
108
What are some of the hazards associated with large volumes of rock and gases emitted during major Plinian eruptions at composite volcanoes?
Gases and fine particles of volcanic ash can cause respiratory distress and poisoning, and ash poses a risk for aircraft.
109
What is the risk associated with the distribution of tephra from large explosive eruptions by high-altitude winds?
Tephra from large explosive eruptions can be distributed around Earth by high-altitude winds, posing risks to respiratory health and causing damage to structures.
110
Describe the accumulation of tephra and its consequences during the Mt. Pinatubo eruption in 1991.
During the Mt. Pinatubo eruption in 1991, tens of centimeters of ash accumulated in fields and on rooftops in the surrounding populated region. Heavy typhoon rains compounded the weight of the tephra, causing roofs to collapse and resulting in casualties.
111
What long-term effect on the atmosphere is associated with adding volcanic particles and gases, as seen in the example of the Laki volcano eruption in 1783-1784?
One long-term effect is cooling. The Laki volcano eruption in 1783-1784 released a massive amount of sulfur dioxide into the atmosphere, forming sulfate aerosols that block incoming solar energy, leading to dramatic cooling in the northern hemisphere.
112
What were the consequences of the massive effusive eruption at the Laki volcano in Iceland in 1783-1784?
The eruption led to serious crop failures in Europe and North America. About 6 million people are estimated to have died from famine and respiratory complications. In Iceland, HF poisoning caused the death of 80% of sheep, 50% of cattle, and over 10,000 human deaths, about 25% of the population.
113
What happens during a typical explosive eruption at a composite volcano?
Tephra and gases are ejected with explosive force, sent high up into the atmosphere. As the eruption proceeds, the decreasing amount of gas in the rising magma leads to the collapse of the eruption column, resulting in pyroclastic flows.
*image 30
114
What causes the collapse of the eruption column, leading to the formation of pyroclastic flows?
As the amount of gas in the rising magma decreases during an explosive eruption, parts of the eruption column become denser than air, causing the column to collapse and flow downward along the flanks of the volcano.
115
What is the characteristic behavior of pyroclastic flows as they move downward along the flanks of a volcano?
Pyroclastic flows pick up speed as they cool and can travel over water, covering long distances. They are capable of traveling for many kilometers.
116
Can pyroclastic flows travel over water, and can you provide examples?
Yes, pyroclastic flows can travel over water. For example, in 1902, the pyroclastic flow from the eruption of Mt. Pelée traveled into the harbour and destroyed several wooden ships. The 1883 eruption of Krakatau's pyroclastic flow traveled 80 km across the Sunda Straits and triggered a tsunami.
117
What is one of the most famous instances of pyroclastic flows, and what were the consequences?
One of the most famous instances of pyroclastic flows occurred when Mt. Vesuvius erupted in 79 CE. It buried the cities of Pompeii and Herculaneum, resulting in the estimated death of around 18,000 people.
118
What is a lahar, and what type of geological event is it associated with?
A lahar is any mudflow or debris flow related to a volcano.
*image 31
119
What can cause lahars during a volcanic eruption, and can you provide an example?
Lahars during a volcanic eruption can be caused by melting snow and ice. An example is the lahar that destroyed the Colombian town of Armero in 1985 when the volcano Nevado del Ruiz caused the failure of an ice dam on a glacial lake, resulting in a lahar that killed 23,000 people in Armero.
120
Can lahars occur without a volcanic eruption, and what are the factors that contribute to their occurrence in such cases?
Yes, lahars can occur without a volcanic eruption. Composite volcanoes tend to be weak and easily eroded, making them susceptible to lahars. An example is the lahars triggered by intense rainfall during Hurricane Mitch in October 1998 in Central America.
121
Describe an instance of lahars occurring due to factors other than a volcanic eruption.
In October 1998, Hurricane Mitch caused extensive damage in Central America, resulting in lahars and debris flows due to intense rainfall. Some regions received almost 2 meters of rain over a few days, leading to approximately 19,000 fatalities.
122
What is an example of lahars occurring as a result of heavy rains weakening rock and volcanic debris on the upper slopes of a volcano?
At Casita Volcano in Nicaragua, heavy rains weakened rock and volcanic debris on the upper slopes, resulting in a debris flow that struck the towns of El Porvenir and Rolando Rodriguez, killing more than 2,000 people. These towns were built without planning approval in an area known to be at risk of lahars.
123
What is sector collapse in the context of volcanoes?
Sector collapse, or flank collapse, refers to the catastrophic failure of a significant part of an existing volcano, leading to the creation of a large debris avalanche.
124
When was sector collapse first recognized as a volcanic hazard, and what event highlighted its occurrence?
Sector collapse as a volcanic hazard was first recognized with the failure of the north side of Mt. St. Helens, particularly during the catastrophic eruption on May 18, 1980.
125
What geological feature formed in the weeks before the Mt. St. Helens eruption, and what triggered the catastrophic failure?
In the weeks before the eruption, a large bulge formed on the side of Mt. St. Helens as magma moved into a magma chamber within the volcano. The catastrophic failure was triggered by a moderate earthquake early on the morning of May 18, which destabilized the bulge.
*image 32
126
What was the consequence of the sector collapse at Mt. St. Helens, and how did it contribute to the subsequent eruption?
The failure exposed the underlying magma chamber, causing it to explode sideways. This exposure led to a Plinian eruption lasting nine hours, as it also revealed the conduit leading to the magma chamber below.
127
Geological Survey geologist Chris Newhall made a list of the six most important signs of an imminent volcanic eruption
1. Gas leaks — the release of gases (mostly H2O, CO2, and SO2) from the magma into the atmosphere through cracks in the overlying rock
2. Bulging — the deformation of part of the volcano, indicating that a magma chamber at depth is swelling or becoming more pressurized
3. Seismicity — many (hundreds to thousands) of small earthquakes, indicating that magma is on the move. The quakes may be the result of the magma forcing the surrounding rocks to crack, or a harmonic vibration that is evidence of magmatic fluids moving underground.
4. Seismicity ceases — a sudden decrease in the rate of earthquake activity. This may indicate that magma has stalled, and that\ something is about to give way
5. Big bump — a pronounced bulge on the side of the volcano (like the one at Mt. St. Helens in 1980), which may indicate that magma has moved close to surface
6. Steam — steam eruptions (phreatic eruptions) that happen when magma near the surface heats groundwater to the boiling point. The water eventually explodes, sending fragments of the overlying rock far into the air.
128
What is the simplest and cheapest way to monitor a volcano?
Seismometers, instruments that detect vibration, are the simplest and cheapest tools to monitor a volcano.
129
How can seismometers provide early warning of volcanic activity?
In areas with multiple volcanoes, strategically placed seismometers can detect changes beneath a volcano, giving early warning of potential eruptions.
130
What should be done if there is seismic evidence of a volcano becoming active?
If there is seismic evidence, additional seismometers should be placed near the source of activity to determine the exact location and depth of the seismic activity.
Placing seismometers nearby helps geologists determine the precise location and depth of seismic activity, aiding in tracking the movement of magma.
131
Why is water vapor relatively easy to detect around a volcano?
Water vapor turns into visible clouds of liquid water droplets, making it easily detectable just by looking
132
What are some gases that are not as obvious and require monitoring around a volcano?
Carbon dioxide (CO2) and sulfur dioxide (SO2) are not as obvious and require monitoring around a volcano.
133
How can changes in the composition of volcanic gases be monitored from a distance?
Infrared devices, either from the ground or the air, can be used to monitor changes in the composition of volcanic gases from a distance.
To obtain more accurate data, sampling the air and conducting chemical analysis is required.
Instruments placed on the ground close to the source of gases can be used to monitor volcanic gases.
Collecting air samples and conducting chemical analysis in a lab is an alternative method for analyzing volcanic gas composition.
134
What are the two main methods for measuring ground deformation at a volcano?
Tiltmeters and GPS technology are the two main methods for measuring ground deformation at a volcano.
A tiltmeter is a sensitive three-directional level that can detect small changes in the tilt of the ground at a specific location.
135
Why is GPS technology more effective than a tiltmeter for measuring ground deformation?
GPS technology provides information on how far the ground has actually moved in east-west, north-south, and up-down directions, making it more effective than a tiltmeter.
136
How can geologists assess the potential for a volcano to erupt in the near future?
By combining information from seismometers, gas monitoring, ground deformation measurements, and careful observations, geologists can assess the potential for a volcano to erupt in the near future.
Geologists can provide an idea of a potential volcanic eruption in the near future, ranging from months to weeks, but not days.
137
Where are Canada's volcanically active regions located?
Canada's volcanically active regions are located in British Columbia and the Yukon Territory.
At least 49 eruptions have occurred in the last 10,000 years within Canada's volcanically active regions.
138
How many volcanic regions are associated with Canada's volcanically active areas, and what are the plate tectonic settings involved?
There are five volcanic regions associated with three types of plate tectonic settings in Canada's volcanically active areas: a subduction zone, a mantle plume, and a continental rift zone
139
What is the cause of the Wrangell Volcanic Belt in Canada?
The Wrangell Volcanic Belt in Canada is the result of subduction beneath the North American Plate.
Volcanoes in the Canadian part of the Wrangell Volcanic Belt erupted between 17.8 and 10.4 million years ago and were fed by lava that seeped up along a leaky transform fault.
*image 33
140
What is the geological setting of southwestern British Columbia in relation to volcanism?
Southwestern British Columbia is at the northern end of the Juan de Fuca subduction zone, part of the Cascade Volcanic Arc extending south through Washington and Oregon.
141
Why has the Canadian part of the Cascade Arc had a lower rate and volume of volcanism compared to U.S. portions?
One reason is that the northern part of the Juan de Fuca Plate is subducting more slowly than the rest of the plate, or else has stalled.
142
What is the Garibaldi Volcanic Belt, and what is its recent volcanic history?
The Garibaldi Volcanic Belt has several volcanic centers, and the most recent volcanic activity in the area occurred 2,350 years ago at Mt. Meager, with significant activity at Mt. Price and Mt. Garibaldi approximately 10,000 years ago.
143
What geological features resulted from volcanic activity in the Garibaldi Volcanic Belt, particularly involving glacial ice?
Lava and tephra built up against glacial ice at Mt. Price and Mt. Garibaldi. The western side of Mt. Garibaldi failed by sector collapse when the ice melted, and eruption beneath glacial ice formed a tuya called The Table.
144
What is the Anahim Volcanic Belt, and what is its geological origin?
The Anahim Volcanic Belt is a chain of volcanic complexes and cones extending from Milbanke Sound to Nazko Cone, interpreted as being related to a mantle plume currently situated close to the Nazko Cone.
145
Where is the mantle plume associated with the Anahim Volcanic Belt located?
The mantle plume associated with the Anahim Volcanic Belt is currently situated close to the Nazko Cone, just west of Quesnel.
146
How is the formation of volcanic features in the Anahim Volcanic Belt related to the movement of tectonic plates?
The North American Plate is moving in a westerly direction at about 2 cm per year with respect to the mantle plume, and the volcanic features were formed as the continent moved over the plume.
*image 34
147
What is the significance of the Rainbow Range in the Anahim Volcanic Belt?
The Rainbow Range, formed at approximately 8 million years ago, is the largest of the older volcanoes in the Anahim Volcanic Belt, with a diameter of about 30 km and an elevation of 2,495 m.
148
Why is the Rainbow Range named as such?
The name "Rainbow" refers to the bright colors displayed by some of the volcanic rocks in the Rainbow Range as they weather.
*image 35
149
Which areas of volcanism in British Columbia are related to rifting or stretching-related fractures?
The Wells Gray-Clearwater volcanic field southeast of Quesnel and the Stikine Volcanic Belt (Northern Cordillera Volcanic Province) are related to rifting or stretching-related fractures in British Columbia.
150
Where is the Stikine Volcanic Belt located, and what is its historical significance?
The Stikine Volcanic Belt, ranging across the northwestern corner of the province, includes Canada's most recent volcanic eruption at the Tseax River Cone around 250 years ago, according to Nisga’a oral history.
151
Describe the Mount Edziza Volcanic Field near the Stikine River.
The Mount Edziza Volcanic Field is a large area with lava flows, sulphurous ridges, and cinder cones. The most recent eruption in this area was about 1,000 years ago.
152
What is unique about Mt. Edziza within the Edziza region?
Mt. Edziza is a composite volcano with rock compositions ranging from rhyolite to basalt, in contrast to the mafic flows and cinder cones dominating the Edziza region. The presence of composite volcanism suggests a magma chamber where magma differentiation is taking place.
