Chapter 11- Volcanism (Week 4) Flashcards
What is a volcano?
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.
What are fissure eruptions?
Fissure eruptions are volcanic eruptions flowing from long cracks in the Earth.
What are the main parts of a volcano?
The main parts of a volcano include a magma chamber, vent or conduit, crater, and the possibility of a flank eruption.
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Describe the process when volcanoes erupt.
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.
What is the difference between a crater and a caldera?
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.
Describe the process of caldera formation.
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.
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What are the main parts of a volcano?
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.
How do fissure eruptions differ from those flowing from mountains?
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
What are the three main types of materials produced by volcanic eruptions?
Volcanic eruptions produce three types of materials: gas, lava, and fragmented debris known as tephra.
Describe the process of gas release during a volcanic eruption.
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
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What factors influence the ease with which lava flows and the structures it forms?
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.
How does the silica content of lava relate to its gas content?
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.
What factors influence the thickness and shape of a lava flow?
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.
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How does the viscosity of lava affect its flow distance?
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.
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How do lava tubes form, and what is their significance in volcanic activity?
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.
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What is pahoehoe lava, and how does it develop a wrinkled texture known as ropy lava?
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.
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What is a’a lava, and how does its texture differ from pahoehoe lava?
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.
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What is blocky lava, and how does it differ from a’a lava?
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.
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How do lava pillows form, and what information can they provide about the past environment?
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.
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What causes the formation of columnar joints in lava flows, and how do they appear?
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.
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What term is used to collectively refer to loose material thrown from a volcano, and what are individual fragments called?
Loose material thrown from a volcano is collectively referred to as tephra, and individual fragments are called pyroclasts.
What are particles less than 2 mm in diameter called, and what do they consist of in volcanic ash?
Particles less than 2 mm in diameter are called volcanic ash, and they consist of small mineral grains and glass.
What are fragments with dimensions between 2 mm and 64 mm called?
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
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What are fragments larger than 64 mm classified as, and how do they differ based on their origin?
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
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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.
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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.
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.
What are the three main types of volcanoes?
The three types of volcanoes are cinder cones (spatter cones), composite volcanoes (stratovolcanoes), and shield volcanoes.
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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.
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.
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
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.
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
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.
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.
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.
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.
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.”
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.
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.
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.
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.
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.
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.
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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.
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.
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.
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.
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.
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
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.
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.
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.
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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.
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.
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.
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.
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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.
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.
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.
