2-28 Volcanic Eruptions
Do Now: Take out your homework and answer the following questions in your notebook. A large volcano with gentle slopes is a A. shield volcano. B. composite volcano. C. cinder cone volcano. Large, steep-sided volcanoes form at convergent plate boundaries. composite A(n) is a depression formed when a volcano’s summit collapses or is blown away by an explosive eruption. Caldera A(n) is a small, steep-sided volcano formed from basaltic lava. Cinder cone
HW Review: How are volcanoes classified?
Volcanoes Quiz Friday, 3/2/18 Volcano formation Types of volcanoes Factors that contribute to volcanic eruptions
EQ: What factors contribute to the eruption style of a volcano?
Volcanic Eruptions When magma surfaces, it might erupt as a lava flow or erupt explosively, sending volcanic ash high into the atmosphere. Volcanic ash: tiny particles of pulverized volcanic rock and glass. Ceniza volcanica: particulas diminutas de roca y vidrio volcanicos pulverizados. Magma chemistry determines a volcano’s eruptive style.
Eruption Style Magma chemistry determines a volcano’s eruptive style. The behavior of a volcano is affected by the amounts of dissolved gases, specifically the amount of water vapor, and the amount of silica (SiO2) a magma contains.
Volcanic eruptions Silica (SiO2) is the main chemical compound in all magmas. Differences in the amount of silica affect magma thickness and its viscosity: a measurement of a liquid’s resistance to flow Viscosidad: medida de la resistencia de un liquido a fluir.
Volcano Eruptions Lavas that are low in silica (thus low viscosity) and the amount of dissolved gases erupt quietly. Lava that is high in silica (thus high viscosity) and dissolved gases result in explosive eruptions.
Volcanic Eruptions – Why dissolved gases cause explosive eruptions. All magmas contain dissolved gases, such as water vapor and small amounts of carbon dioxide and sulfur dioxide. As magma moves toward the surface, pressure decreases and the gases are less likely to stay dissolved in the magma. Eventually, bubbles begin to form from the gas. In high-viscosity lavas, the gases cannot easily escape, often resulting in explosive eruptions. When gases escape above ground, the lava, ash, or volcanic glass that cools and crystallizes has holes.
Effects of Volcanic Eruptions The effects of lava flows, ash fall, pyroclastic flows, and mudflows can affect all life on Earth. Although lava flows tend to be slow moving, they threaten communities nearby. Mount Etna in Sicily, Italy, is one of the world’s most active volcanoes. People that live near the volcano are accustomed to evacuations due to frequent eruptions. http://abcn.ws/2nV6EfR
Effects of Volcanic Eruptions Volcanic ash can affect air quality and can cause serious breathing problems. Ash can disrupt air traffic and cause engines to stop mid-flight as shards of rock and ash fuse onto hot engine blades. Large quantities of ash can also affect climate by blocking out sunlight and cooling Earth’s atmosphere. Ash cloud from Mount St. Helens over Ephrata, Washington (145 miles downwind), after the May 18 1980 eruption
Effects of Volcanic Eruptions Volcanic eruptions affect climate when volcanic ash in the atmosphere blocks sunlight. The average global temperature decreases as less sunlight reaches Earth’s surface. The 1991 Mount Pinatubo eruption caused temperatures to decrease by almost one degree Celsius in one year.
Effects of Volcanic Eruptions The thermal energy a volcano produces during an eruption can melt snow and ice, creating meltwater that mixes with mud and ash on the mountain, forming mudflows. Left: Mudflow in Alaska; Right: mudflow in Chile, 2015
Effects of Volcanic Eruptions Explosive volcanoes can produce fast-moving avalanches of hot gas, ash, and rock called pyroclastic flows. Pyroclastic flows can travel more than 100 km/hr with temperatures greater than 1000C. In 1980, Mount St. Helens produce a pyroclastic flow that killed 58 people and destroyed 1 billion km3 of forest. https://youtu.be/UK--hvgP2uY
Predicting Volcanic Eruptions Volcanic eruptions can be predicted. Moving magma can cause ground deformation, a change in shape of the volcano, and a series of earthquakes called an earthquake swarm. Volcanic gas emissions can increase. Ground and surface water can become more acidic. https://youtu.be/kc_T4buG2gE
Key Concept Builder: Eruption Style When told to move, you will stand up, hand up, and pair up with a partner and answer the first question on the Volcanoes Key Concept Builder worksheet. After 1 minute, you should thank your partner and then stand up, hand up, and pair up to find a different partner to work on the next question. Repeat until all questions are answered.