NC Earth Science Essential Standards EEn. 2.1 Explain how processes and forces affect the Lithosphere. EEn. 2.1.1 Explain how the rock cycle, plate tectonics, volcanoes, and earthquakes impact the Lithosphere. EEn. 2.1.2 Predict the locations of volcanoes, earthquakes, and faults based on information contained in a variety of maps. EEn. 2.1.3 Explain how natural actions such as weathering, erosion (wind, water, and gravity), and soil formation affect Earth s surface. EEn. 2.1.4 Explain the probability of and preparation for geohazards such as landslides, avalanches, earthquakes, and volcanoes in a particular area based on available data. [National Science Content Standards:] UPC.1, UCP.2, UCP.3, UPC.4, UPC.5; A.1, A.2; B.4, B.6; D.1, D.2, D.3; F.4, F.5, F.6; G.3;
Reading Assignment: Read ; pages: 470-487 Objective: Vocabulary: Explain how the rock cycle, plate tectonics, volcanoes, and earthquakes impact the Lithosphere. Predict the locations of volcanoes, earthquakes, and faults based on information contained in a variety of maps. viscosity Pluton Batholith Stock Laccolith Sill Dike Vent Crater Caldera Shield volcano Cinder-cone volcano Tephra Pyroclastic flow Hot spot
Volcanic Activity The ash that spews from some volcanoes can form billowy clouds that travel around the world before raining back down to Earth. In the last 10 000 years, more than 1500 different volcanoes have erupted-providing evidence that Earth is indeed geologically active.
How Magma Forms All volcanoes are fueled by magma deep beneath Earth s surface. Magma is a mixture of molten rock, suspended minerals, and dissolved gases and forms when temperatures are high enough to melt rocks. Depending on their composition, most rocks melt at temperatures between 800ºC 1200ºC. These temperatures exist at the base of the lithosphere and in the asthenosphere (plastic like portion of the mantle), beneath the lithosphere. The other factors that affect the formation of magma beside temperature are pressure and water.
Pressure Pressure, which increases with depth, is one factor that determines whether rocks will melt to form magma. As pressure increases, the temperature at which a substance melts also increases. Due to the effects of pressure, most of the rocks in Earth s lower crust and upper mantle do not melt to form magma. 1100
Magma Unit 5: Dynamic Earth Lesson 2b Volcanic Activity EEn 2.1.1 and 2.1.2 Water The presence of water also influences whether a rock will melt. At any given pressure, a wet mineral or rock will melt at a lower temperature than the same mineral or rock under dry conditions.
Types of Magma Magma The three major types of magma are: basaltic magma, andesitic magma, and rhyolitic magma. Basaltic magma has the same composition as basalt and fuels the volcanoes that make up the Hawaiian Islands and Surtsey, which is south of Iceland. Andesitic magma has the same composition as andesite and fuels Mount St. Helens in Washington State and Tambora in Indonesia. Rhyolitic magma has the same composition as granite and fueled the dormant volcanoes in Yellowstone National Park.
According to the map the most active volcanoes are located on the edges of the Pacific Ocean plate.
Magma Composition A number of factors determine the composition of magma. Viscosity is the internal resistance to flow; the higher the viscosity, the slower the flow. Flows like: Warm honey Room temp. honey Chilled honey The hotter the magma/lava is, the lower the viscosity; and the easier it flows; Magmas/lavas high in silica have higher viscosities; and resist flowing; The amount of silica content in magma/lava increases the viscosity; high in silica produce higher viscosities;
Basaltic Magma (Hawaiian Islands) Basaltic magma typically forms when rocks in the upper mantle melt. Most basaltic magma rises relatively rapidly to Earth s surface and reacts very little with crustal rocks due to its low viscosity (this magma flows quickly). Basaltic magma contains small amounts of dissolved gases and silica due to its low viscosity Basaltic lava temperatures: 1000ºC 1250ºC
Andesitic Magma (Mount St Helen s) Andesitic magma is found along continental margins, where oceanic crust is subducted into Earth s mantle. The source material for this magma can be either oceanic crust or oceanic sediments. Andesitic magma contain about 60% silica, the high content results in having an intermediate viscosity, Volcanoes having andesitic magma are said to have intermediate eruptions. Andesitic magma temperatures: 800ºC 1000ºC
Rhyolitic Magma (Yellowstone Calderas) Rhyolitic magma forms when molten material rises and mixes with the overlying silica- and water-rich continental crust. The high viscosity of rhyolitic magma inhibits its movement (very slow moving magma/lava). The resistance to flow, along with the large volume of trapped gasses within this magma, makes these volcanoes very explosive! Rhyolitic magma temperatures: 650ºC 800ºC
Intrusive Activity Magma, because it is molten, is less dense than surrounding rocks. This density difference forces magma to move upward and eventually come into contact with, or intrude into, the overlying crust.
Intrusive Activity Intruding magma can affect the crust in several ways: A. Magma can force the overlying rock apart and enter the newly formed fissures. B. Magma can cause blocks of rock to break off and sink into the magma, melting or partially melting rock. C. Magma can melt the rock into which it intrudes.
Plutons Cooling magma forms minerals; over a very long period of time, minerals combine to form intrusive igneous rock bodies. Plutons are intrusive igneous rock bodies that can be exposed at Earth s surface as a result of uplift and erosion and are classified based on their size, shape, and relationship to surrounding rocks.
Batholiths, the largest plutons, Irregularly shaped masses of coarse-grained igneous rocks; Covering at least 100 km 2 and take millions of years to form. Common in the interior of major mountain chains, many batholith in North America are composed primarily of granite, most common rock found in plutons Gabbro, diorite, basalt, and andesite may also be found in batholiths.
Stocks are irregularly shaped plutons that are similar to batholiths but smaller in size Both batholiths and stocks cut across older rocks and generally form 10 30 km beneath Earth s surface.
Laccolith are a mushroom-shaped pluton with a round top and flat bottom resulting from a magma intrusion into parallel rock layers close to Earth s surface. When magma intrudes into parallel rock layers close to Earth s surface, some of the rocks bow upward due to the intense heat and pressure and, a laccolith forms. Compared to batholiths and stocks, laccoliths are relatively small; they are, at most, up to 16 km wide. Laccoliths exist in the Black Hills of South Dakota, Henry Mountains of Utah, and Judith Mountain of Montana.
Sills and Dikes A sill forms when magma intrudes parallel to layers of rock, and can range from a few cm to hundreds of meters A dike is magma that cuts across preexisting rocks (not parallel) and ranges from a few cm to several meters wide and up to tens of kilometers long While the textures of sills and dikes vary, many are coarse grained, indicating they were formed deep in Earth s crust, where magma cooled relatively slowly.
Plutons and Tectonics Many plutons, especially batholiths, are formed as the result of mountain-building processes. Batholiths are thought to have formed as a result of continental-continental and oceanic-oceanic convergent plate boundaries. The plutons that form deep beneath Earth s surface represent the majority of igneous activity on our planet.
Anatomy of a Volcano When magma reaches Earth s surface it is called lava. A vent is where lava erupts through an opening in the crust. As lava flows out onto the surface, it cools and solidifies around the vent, eventually accumulating to form a mountain known as a volcano. A crater is a bowl-shaped depression at the top of a volcano that is connected to the magma chamber by a vent.
Anatomy of a Volcano Volcanic craters are usually less than 1 km in diameter. Calderas are large depressions up to 50 km in diameter that can form when the summit or the side of a volcano collapses into the magma chamber that once fueled the volcano.
How Calderas form: Due to repeated volcanic eruptions The underlying magma chamber begins to empty. The emptied magma chamber no longer able to carry the weight of the overlying volcano, And the roof of the chamber collapses, The caldera, can fill with water and eventually form into a lake.
Types of Volcanoes The appearance of a volcano depends on two factors: The type of material that forms the volcano The type of eruptions that occur Based on these two criteria, three major types of volcanoes have been identified: Shield volcanoes Cinder-cone volcanoes Composite volcanoes
Shield Volcanoes (largest volcanoes) A shield volcano a mountain with broad, gently sloping straight sides, and a nearly circular base that forms when layer upon layer of basaltic lava accumulates during nonexplosive eruptions. Basaltic lava have low viscosity and are less explosive due to a relatively small amount of gasses and silica Shield volcanoes are by far the largest; and have straight, gentle slopes. Shield Volcano: Mauna Loa
Cinder-Cone Volcanoes (smallest volcanoes) A cinder-cone volcano is a generally small, steepsided, concave sloped, volcanos that forms when material ejected high into the air falls back to Earth and piles up around the vent. The magma that fuels these volcanoes contains more water and silica than shield volcanoes, which makes them more explosive in nature. Cinder-cone volcanoes are the smallest; and have steep concave slopes. Cinder-Cone Volcano: Izalco Volcano Most are less than 500 m high.
Composite Volcanoes Composite volcanoes (also known as a stratovolcano) are large, concave sloped, volcanoes that form when layers of volcanic fragments alternate with lava. The magma that forms composite volcanoes commonly contains large amounts of silica, water, and gases, making these volcanoes violently explosive. Composite volcanoes also have concave slopes. Composite Volcano: Mt Rainier
Volcanic Material Tephra are rock fragments thrown into the air during a volcanic eruption and can cause tremendous damage and kill thousands of people. Tephra are classified by size, the smallest being dust (less than 0.25 mm) and ash (0.25 2 mm). Somewhat larger fragments are called lapilli, or little stones (2 64 mm in diameter). The largest tephra thrown from a volcano include angular volcanic blocks and may be cooled to form rounded or streamlined volcanic bombs, both of which can be the size of a house or larger.
Pyroclastic Flows A pyroclastic flow is a cloud of volcanic gas, dust, and other tephra traveling at speeds of nearly 200 km/h. The temperature at the center of a pyroclastic flow can exceed 700ºC (1292ºF). One of the most widely known and deadly pyroclastic flows occurred in 1902 on Mount Pelée on the island of Martinique in the Caribbean. More than 29,000 people died due to suffocation or burns.
Where do volcanoes occur? Most volcanoes form at plate boundaries. About percent of all volcanoes are found along convergent boundaries. About 15 percent are found along divergent boundaries. Only about 5 percent of extrusive igneous activity occurs far from any plate boundary.
Convergent Volcanism Volcanoes Convergence involving oceanic plates creates subduction zones, and the magma generated is forced upward through the overlying plate and forms volcanoes when it reaches the surface. The volcanoes associated with convergent plate boundaries form two major belts: The larger belt, the Circum- Pacific Belt, is also called the Pacific Ring of Fire. The smaller belt is called the Mediterranean Belt.
Divergent Volcanism (15% formed) At divergent plate boundaries (where plates are moving apart), magma is forced upward into the fractures and faults that form as the plates separate. These areas of major faults/fractures are called rift zones. Most of the world s rift volcanism occurs under water along ocean ridges. This type of volcanism results in the formation of new ocean floor during the seafloor spreading process.
Hot Spots (5% formed) Some volcanoes are located far from plate boundaries and form as the result of hot spots. Hot spots are unusually hot regions of Earth s mantle where high-temperature plumes of mantle material rise toward the surface A plume does not move laterally, which results in a trail of progressively older volcanoes that formed as a plate moved over a hot spot.
Hot Spots The Hawaiian Islands continue to rise above the ocean floor as the Pacific Plate moves slowly over a hot spot. The rate and direction of plate motion can be calculated from the positions of volcanoes in a chain that has formed over a hot spot.
Hot Spots Note that Meiji is at one end of the Emperor Seamounts, while Hawaii is at the southern most end of the Hawaiian Islands. The bend in the chain of islands at Daikakuji Seamount records a change in the direction of the Pacific Plate that occurred about 43 million years ago.
Flood Basalts In addition to seamount chains, hot spots can result in the formation of flood basalts. Flood basalts erupt from fissures rather than a central vent and form flat plains or plateaus rather than volcanic mountains. The volume of basalt in these eruptions can be tremendous, as seen in the Columbia River Basalts in the Northwestern United States and the Deccan Traps in India.
Magma Unit 5: Dynamic Earth Lesson 2b Volcanic Activity EEn 2.1.1 and 2.1.2 Section Assessment 1. Match the magma types with their characteristics. B basaltic A andesitic C rhyolitic A. intermediate viscosity content, forms from oceanic crust and oceanic sediments B. low viscosity and gas content, forms from rocks in the upper mantle C. high viscosity, forms from continental crust materials
Magma Unit 5: Dynamic Earth Lesson 2b Volcanic Activity EEn 2.1.1 and 2.1.2 Section Assessment 2. What would be the likely effect if the volcano at Yellowstone National Park were to erupt? Why? It would most likely be a devastating eruption because it would be fueled by rhyolitic magma, which has a very high viscosity and gas content.
Magma Unit 5: Dynamic Earth Lesson 2b Volcanic Activity EEn 2.1.1 and 2.1.2 Section Assessment 3. Identify whether the following statements are true or false. true It is unlikely that Mount Kilauea in Hawaii will explosively erupt. true Wet granite will melt at a lower temperature than dry granite. false A liquid with a high viscosity will also have a high flow rate. true Major eruptions of Mount St. Helens in Washington state and Mount Fuji in Japan would probably be similar in nature.
Intrusive Activity Unit 5: Dynamic Earth Lesson 2b Volcanic Activity EEn 2.1.1 and 2.1.2 Section Assessment 1. Match the following terms with their definitions. D batholith B stock E laccolith A sill dike C A. a pluton that forms when magma intrudes parallel to layers of rock B. an irregularly shaped pluton that is similar to a batholith but smaller in size C. a pluton that cuts across preexisting rocks D. an irregularly shaped pluton that covers at least 100 km 2 E. a mushroom-shaped pluton with a round top and flat bottom
Intrusive Activity Unit 5: Dynamic Earth Lesson 2b Volcanic Activity EEn 2.1.1 and 2.1.2 Section Assessment 2. How do sills and laccoliths differ? Sills and laccoliths both result from magma intrusions that are parallel to existing rock. Laccoliths push the overlying layers upward, creating a distinct mushroom-shape when they cool and solidify. Sills are generally thinner and do not cause a noticeable bump in the surface.
Intrusive Activity Unit 5: Dynamic Earth Lesson 2b Volcanic Activity EEn 2.1.1 and 2.1.2 Section Assessment 3. What surface feature are batholiths most associated with? Batholiths are found at the cores of many of Earth s mountain ranges.
Volcanoes Unit 5: Dynamic Earth Lesson 2b Volcanic Activity EEn 2.1.1 and 2.1.2 Section Assessment 1. Match the following terms with their definitions. A vent C crater D tephra E pyroclastic flow caldera B A. an opening in the crust from which lava flows B. depression caused by a collapsed magma chamber C. a bowl-shaped depression around an opening in the crust D. volcanic materials that are thrown into the air during a volcanic eruption E. a cloud of rapidly moving, extremely hot volcanic material
Volcanoes Unit 5: Dynamic Earth Lesson 2b Volcanic Activity EEn 2.1.1 and 2.1.2 Section Assessment 2. How can chains of volcanoes that form over a hot spot track plate movement? The hot spot is in a fixed location. All of the volcanoes in the chain were over the hot spot when they formed. The volcanoes movement and the direction of the chain s alignment indicates the movement of the plate.
Volcanoes Unit 5: Dynamic Earth Lesson 2b Volcanic Activity EEn 2.1.1 and 2.1.2 Section Assessment 3. Identify whether the following statements are true or false. true Many cinder-cone volcanoes are less than 500 m high. false Volcanism is more common along divergent boundaries as compared to convergent boundaries. false The Mediterranean Belt is also known as the Ring of Fire. true It can be 700ºC in the center of a pyroclastic flow.
Chapter Assessment Unit 5: Dynamic Earth Lesson 2b Volcanic Activity EEn 2.1.1 and 2.1.2 Multiple Choice 1. Andesitic magma has a silica content of about percent. a. 50 c. 70 b. 60 d. 80 Basaltic magma has a silica content of about 50%. Rhyolitic magma has a silica content of about 70%.
Multiple Choice Chapter Assessment 2. Which of the following is the largest type of pluton? a. stock c. batholith b. laccolith d. sill Batholith plutons are common in the interiors of many mountain chains and are the result of the magma generated during subduction at convergence zones.
Multiple Choice Chapter Assessment 3. Shield cone volcanoes are fueled by what kind of magma? a. basaltic c. tephra b. andesitic d. rhyolitic Basaltic magma has a low viscosity and erupts with low explosiveness. This allows the lava to flow down the mountain s slopes and continually add to the mountain.
Multiple Choice Chapter Assessment 4. Where is divergent volcanism generally found? a. ocean rifts c. ocean trench b. mid-plate d. Abyssal plains Divergent volcanism is almost entirely found underwater (Iceland is the major exception) at ocean rifts. Through divergent volcanism, new sea floor is created as the plates spread apart.
Multiple Choice Chapter Assessment 5. Where are most active volcanoes located? a. divergent c. hot spots boundaries b. convergent d. transform boundaries boundaries Most active volcanoes are in the either the Circum-Pacific or Mediterranean Volcanic Belts, which are located on convergent boundaries.
Short Answer Chapter Assessment 6. How does the presence of water influence whether a rock will melt? At any given pressure, a wet mineral or rock will melt at a lower temperature than the same mineral or rock under dry conditions.
Short Answer Chapter Assessment 7. What is the relationship between viscosity and the temperature of magma or lava? The hotter the magma or lava, the lower the viscosity.
True or False Chapter Assessment 8. Identify whether the following statements are true or false. false Andesitic magma has more explosive potential than rhyolitic magma. false A dike forms when magma intrudes parallel to layers of rock. true Cinder-cone volcanoes can form on the flanks of a shield volcano. true Many of the volcanoes in the Cascade range are composite volcanoes. true The hot spot under Hawaii has existed for at least 75 million years.
Section 18.1 Study Guide Unit 5: Dynamic Earth Lesson 2b Volcanic Activity EEn 2.1.1 and 2.1.2 Section 18.1 Main Ideas Temperature, pressure, and the presence of water are factors that affect the formation of magma. As pressure increases, the temperature at which a substance melts also increases. At any given pressure, the presence of water will cause a substance to melt at a lower temperature than the same substance under dry conditions. There are three major types of magma: basaltic magma, andesitic magma, and rhyolitic magma. These magmas differ in the source rock from which they form, viscosity, silica content, gas content, and explosiveness. Basaltic magma is the least explosive magma; rhyolitic magma is the most explosive.
Section 18.2 Study Guide Unit 5: Dynamic Earth Lesson 2b Volcanic Activity EEn 2.1.1 and 2.1.2 Section 18.2 Main Ideas Magmatic intrusions affect the crust in several ways. Magma can force overlying rock apart and enter the newly formed fissures. Magma can also cause blocks of rock to break off and sink into the magma chamber. Magma can melt the rock into which it intrudes. Batholiths, stocks, sills, dikes, and laccoliths are plutons that are classified according to their size, shape, and relationship to surrounding rocks. Batholiths are the largest plutons and often form the cores of many of Earth s major mountain chains.
Section 18.3 Study Guide Unit 5: Dynamic Earth Lesson 2b Volcanic Activity EEn 2.1.1 and 2.1.2 Section 18.3 Main Ideas Lava flows onto Earth s surface through a vent. Over time, multiple lava flows may accumulate to form a volcano. A crater is a depression that forms around the vent at the summit of a volcano. A caldera is a large crater that forms when a volcano collapses during or after an eruption. There are three types of volcanoes: shield volcanoes, cinder-cone volcanoes, and composite volcanoes. Rock fragments ejected during eruptions are called tephra.
Section 18.3 Study Guide Unit 5: Dynamic Earth Lesson 2b Volcanic Activity EEn 2.1.1 and 2.1.2 Section 18.3 Main Ideas Most volcanoes form along convergent and divergent plate boundaries. Volcanoes also form over hot spots, which are unusually hot areas in the mantle that are stationary for long periods of time. Flood basalts form when lava flows from fissures to form flat plains or plateaus.