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Volcanism
Science March 2023
| Question | Answer |
|---|---|
| A volcano: | the landform structure created overtime as magma makes it to the surface and erupts |
| Volcanism: | act of magma forming and moving toward the surface (sometimes erupting sometimes not) |
| The difference between magma and lava | Magma is hot, liquid molten rock that is underground and lava is above the surface. |
| Describe how a volcano forms and be able to label/describe all the parts (magma chamber, vent, conduit, lava, crater, pyroclastics) | A volcano is a landform that is created when magma reaches the surface through a conduit to an opening in earth’s crust. (vent) A crater is a ring structure around a vent, created by erupted materials. |
| Describe Aa lava in terms of viscosity and what the cooled rock characteristics are like | Aa lava has a rough and jagged surface with broken lava blocks and clinkers. This is due to high viscosity, it is felsic, has more holes because gas expands and lava hardens around it. |
| Describe Pahoehoe lava in terms of viscosity and what the cooled rock characteristics are like | Pahoehoe lava has a smooth surface and is often wrinkled due to low viscosity. This causes less holes because it closes up gas escapes and lava flows easier. |
| A single block of Aa lava is called a | A clinker. |
| Viscosity: | Resistance to flow |
| True or false: high viscosity is slower flowing than low viscosity lava | True, low viscosity will flow more easily and faster because it has a low resistance to flow. |
| Viscosity of magma/lava is affected by which two variables? | The composition-More silica in magma the higher the viscosity, the slower it will flow Temperature- the hotter magma is the lower the viscosity will be and the faster and easier it will flow. |
| What is silica and why does it affect viscosity? | More silica in magma the higher the viscosity, the slower it will flow. The less silica in magma, the lower the viscosity and the faster it will flow. |
| When the temperature of lava is higher, the viscosity is lower (higher, lower) | Lower |
| When the silica content of lava is higher, the viscosity is higher (higher, lower) | Higher |
| Which will have a more explosive eruption, a magma with a high silica content and low temp or a magma with a low silica content and high temp? Explain why. | Lots of silica in magma can lead to gas and pressure to build up, which leads to an eruption. |
| List the 3 compositions of magma from highest silica to lowest | Felsic-highest silica content Intermediate-second highest silica content Mafic-lowest in silica |
| What are the 3 types of things that erupted from a volcano? | Lava, pyroclastics,gas |
| What are the 3 main gasses erupted from volcanoes? | Water vapor, Carbon dioxide, and sulphur dioxide |
| What are the 4 types of pyroclastics in order from smallest to largest | Ash Lapilli . blocks & bombs |
| Lapilli: | Button shaped droplets of molten lava that are eject from a volcano during an eruption. They fall to earth while at least partially molten. |
| Blocks and ASH: | -Blocks are solid during an eruption and transport. -Ash- is the smallest pyroclastic type and most deadly hazard. |
| Bomb: | Bomb- A pyroclastic with a diameter greater than 2.5 inches. They are hurled into the air and as it cools it forms a spindle shape. |
| List the 6 volcanic hazards we learned in this unit (in order) | Lava Poison gas pyroclastics(ash) Pyroclastic flow Lahar Tsunamis & earthquakes |
| Why is lava typically not that dangerous? | bc It is slow flowing at .25 mph. To avoid death by lava, just to step out of the way. 1977, Mt. Niyargongo’s crater wall of lava broke in the middle of the night. It’s steep volcano, lava lake & composition of lava makes it fast flowing & dangerous. |
| Why is volcanic gas typically not that dangerous? Which volcanic gas eruption killed 1,800 people? | Because it escapes into the atmosphere, diluting it to non dangerous levels.1986, Lake Nyos Cameroon sits above the vent of a volcano. disturbance to the dissolved carbon dioxide at bottom of the lake, heavy cloud of gas was released/rolled down volcano. |
| Why is ash the most hazardous of all the pyroclastics despite being the smallest? | It is tiny pieces of glass volcanic material and if you inhale it, it will cut your lungs. Also the weight of the ash can collapse buildings .An indirect effect of ash is it reaching the atmosphere and causing climate change. |
| Give an example of when ash caused climate change impacted the world. | 1815 Mt Tambora, Indonesia was in darkness for a week because the volcanic ash and gas reached the stratosphere where the jetstream carried it across the Pacific Ocean. The ash clouds cover incoming solar radiation. |
| how did ash from Indonesia mpact civilization as far away as Concord? | the volcanic ash and gas reached the stratosphere where the jetstream carried it across the Pacific Ocean. Since the ash covered solar radiation, it snowed every day in Concord causing crop failure, migration, and starvation. |
| What are pyroclastic flows and why are they so dangerous? | A pyroclastic flow is a ground hugging avalanche made of hot volcanic gas and pyroclastics. It is so dangerous because of its high speed of 100-430 mph and high temperatures greater than 500°. |
| Describe volcano, year, location and set-up in which pyroclastic flow was deadly to 30,000 people. | 1902 Mt Pele, a Caribbean island of Martinique hada Horizontal blast & pyroclastic flow kills 30,000 leaving only 1 survivor |
| What are lahars and why are they so dangerous? | Lahars are mudflows made of pyroclastic material and water. The material flows down from a volcano, typically along a river valley and can be triggered by melting snow/glaciers at the summit of the volcano or from heavy rains. The viscosity is similar to |
| Describe a volcano, year, location and set-up in which a lahar was deadly to thousands. | 1985 Nevada Del Ruiz, Columbia was the tallest volcano in Colombia. The Eruption melted ice and snow on the volcano and 21,000 lost lives to lahar. |
| Describe a volcano, year, location and set-up in which a tsunami was deadly to thousands. | Krakatoa 1883, Indonesia’s tsunami was the loudest sound ever heard and was heard 2000 km away. Tsunami waves as tall as 46 m killed 36,000 people on surrounding islands and collapse ⅔ of the volcano. |
| more built up gas= | more explosive eruption, lots of pyroclastics, less lava |
| What are the two styles of volcanic eruption? | Effusive is non explosive with lots of lava. Explosive blasts magma into bits that burst out of the volcano as clouds of pyroclastics and gas. |
| An eruption that has a lot of lava and very little pyroclastic material, low on the VEI scale, would be considered what type of eruption? | An effusive eruption. |
| An eruption that has a little lava and mostly pyroclastic material, high on the VEI scale would be considered what type of eruption? | Explosive eruption. |
| Would low or high viscosity lava cause an explosive style eruption? Why? | High viscosity caused an explosive eruption because the higher the viscosity the higher the silica and the higher silica content, the more likely to explode. Felsic lava is the most explosive because it is high viscosity and has a high silica content. |
| What are the 3 types of volcanic cones? | Shield volcano, Cinder cone, Composite cone. |
| Which of the 3 is mostly pyroclastics? | Composite Volcanoes. |
| Which of the three is formed by the lowest viscosity magma? How does this affect the eruption type, shape and size of the volcano? | -Shield volcanoes have basaltic lava=low viscosity. It tends to flow long distances before hardening & builds up in layers to form the shield volcanoes. They tend to discharge basaltic lava, making them less explosive than other types of volcanoes. |
| Which of the 3 cones has the most explosive eruptions with the greatest VEI? | Composite volcanoes. |
| Which of the 3 cones only erupts once and how does that affect the size of the cone? | Cinder Cones |
| Which of the three is formed by intermediate composition magma? How does this affect the eruptive materials and shape of the cone? | Composite volcanoes have intermediate magma which makes the volcano more explosive, build up of gas pressure, hardened lava flows and pyroclastic materials. |
| Mt. St. Helens is an example of which type? | Composite Cone. |
| The Volcanoes of Hawaii (Mauna Loa, Kiluea) are an example of which type? | Shield Volcano. |
| Paricutin of Mexico is an example of which type? | Cinder Cone |
| Pyroclastics from explosive eruptions spew into the air and rain down next to the vent causing the volcano to grow in size, making the slope steep | Composite volcanoes develop when layers of materials form successive, explosive eruptions accumulate around a vent. (hardened lava flows & pyroclastic material) |
| Lava from effusive eruptions flow outwards, with low viscosity it can flow for long distances increasing the __ of the volcano making the slope less steep. | In shield volcanoes, basaltic lava has a low viscosity so it flows for long distances before hardening. It can build up in layers, giving the volcano a broad base. |
| What can the shape of the volcano help you to predict about the volcano that may be useful to know? | Shield volcanoes are wide, not steep and broad Composite volcanoes are very steep, has a smaller central crater/vent Cinder cones are less steep than composite cones and have a wider crater. |
| What is a caldera? How does it form? | A caldera is a large basin, formed when magma beneath a volcano is released after the top of the volcano collapses. |
| Why does Yellowstone have a caldera instead of a volcanic cone due to the style of volcanism it has? | At yellowstone, beneath earth’s surface, magma heats the water which feeds hot springs and geysers. |
| All that remains of the super explosive eruption that covered the western US in a blanket of ash is a caldera filled with geysers and hotsprings | Yellowstone |
| Carbon Dioxide eruption responsible for killing 2000 people in Cameroon | Lake Nyos 1968 |
| killed 30,000 in the town of St. Pierre by pyroclastic flow, one survivor | Mt Pele 1902 |
| Cinder cone in Dionisio's cornfield | Paricutin Mexico 1943 |
| fastest lava in the world | Mount Nyiragongo 1977 |
| Killed Harry Truman with a Lahar in 1980 | Mount St. Helens |
| Rift eruption that threatened to close of an icelandic harbor | Eldfell Rift Eruption. 1973 |
| Most active volcano in Hawaii | Kilauea |
| What are the 3 ways magma is formed? | Partial melting/composition -subduction boundaries Decompression melting-divergent boundaries melting due to decompression?-hotspots |
| Contrast the viscosity, silica content and temperature of magma created at subduction boundaries | At subduction boundaries, there is intermediate magma which has a higher silica content, higher viscosity, and lower temperature. |
| Contrast the viscosity, silica content and temperature of magma created at Divergent boundaries | At divergent boundaries, there is mafic magma which has a low viscosity, low in silica and has a hotter temperature because the hotter magma is the lower the viscosity will be and the faster and easier it will flow. |
| What causes the magma to form at divergent boundaries? | Plates pull apart: pressure on underlying rocks = decompression melting and at this boundary, magma is basaltic/mafic. |
| What causes the magma to form at subduction boundaries | Subduction of oceanic crust leads to partial melting of the asthenosphere and pools under crust, heats and melts crust above. Intermediate/Andesitic composition magma higher viscosity and lots of dissolved gas, so it tends to erupt Explosively |
| Contrast the viscosity, silica content and temperature of magma created at hotspots under Continental crust | Continental crust=felsic, so magma formed on land is felsic, more explosive, higher viscosity, higher in silica, lower in temperature. |
| Contrast the viscosity, silica content and temperature of magma created at hotspots under oceanic crust | Oceanic crust=mafic, so magma formed in ocean is mafic, lower in silica, hotter, lower viscosity |
| What composition magma is formed at subduction boundaries? | Intermediate/Andesitic composition magma is found at subduction boundaries which has a higher viscosity and lots of dissolved gas, leading to explosive eruptions. |
| What is partial melting and describe where it happens | At subduction boundaries, subduction of oceanic crust leads to partial melting of the asthenosphere. The partial melt pools under crust, heat and melt crust above. Partial melting is just melting some of the asthenosphere, certain minerals. |
| What composition magma forms at divergent boundaries? | Mafic magma is formed at divergent boundaries which has a low viscosity and less dissolved gas trapped in it, causing effusive eruptions. |
| What composition magma forms at hot spots on land vs. in the ocean? | Felsic on land, mafic in ocean. - Heating continental crust from below causes felsic magma. Heating oceanic crust from below causes mafic magma |
| What are the two categories of igneous rocks based on where they form? Describe each. | Intrusion(magma chamber) -formed as magma cools underground Extrusion(above the surface)- formed from lava or as pyroclastics. |
| A rock that solidified very rapidly and therefore has gas holes is said to have a ___ | Vesicular texture. Vesicular- pumice, scoria. |
| A rock that solidified very rapidly and therefore has a very smooth and shiny look to it is said to have a ___ texture | a Glassy texture Glassy- obsidian |
| A rock that solidified pretty quickly, like as part of a lava flow, would end up with such small mineral crystals that you cannot usually see them without a microscope. These rocks are said to have FINE texture. | Fine -rhyolite, andesite, basalt |
| A rock that had a two part cooling history interrupted by eruption which has some large crystals and some microscopic mineral crystals is said to have a -PORPHYRITIC texture. | Porphyritic |
| A rock that solidified slowly, like over hundreds of years from a cooling magma chamber will grow large visible mineral crystals and is said to have a Coarse texture. | Coarse-granite, diorite,gabbro |
| In Igneous rocks, it can be said that as length of cooling time increases, crystal size INCREASES. | Increases Slow cooling time=coarse grained=large crystals. |
| Igneous rocks that are lightest in color are FELSIC in composition, meaning high in SILICA. | Felsic = high in silica=light color |
| Igneous rocks that are intermediate in color are Intermediate/andesitic in composition | Intermediate/andesitic |
| What is an intermediate composition intrusive rock called? What igneous rock forms from mafic lava? | Diorite=intermediate, intrusive Mafic lava-Gabbro, basalt, scoria |
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iramirez26