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.2, UCP.4; A.2; D.3; E.1, E.2; G.1, G.3;
Reading Assignment: Read ; pages: 522-539 Objective: 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. Vocabulary: isostasy Isostatic rebound orogeny Pillow basalt Uplifted mountain Fault-block mountain
Earth s Topography Looking at a globe, you will notice 70% of Earth s surface is below sea level; and the remaining 30% lies above the ocean s surface. Most of Earth s elevations cluster around two main elevation modes: 0 to 1 km above sea level and 4 to 5 km below sea level. These two modes dominate Earth s topography and reflect the basic differences in density and thickness between continental and oceanic crust. Average densities: - Continental crust (granite) 2.8 g/cm 3 ; - Oceanic crust (basalt) 2.9 g/cm 3 ; - Mantle is 3.3 g/cm 3 ;
Earth s Topography The different densities of basalt and granite displace different amounts of the mantle, and these rock types thus float at different heights. The slightly higher density of oceanic crust (basalt) causes it to displace more of the mantle than the same thickness of continental crust (granite) does. Continental crust extends deeper into the mantle because of its thickness, and it rises higher above Earth s surface than oceanic crust because of its lower density.
Isostasy: is a condition of equilibrium that describes the displacement of the mantle by Earth s oceanic crust and continental crust. In a state of isostatic equilibrium, the force of gravity on the mass of crust involved is balanced by the upward force of buoyancy. Mountains have thick roots that buoyantly support the overlaying material. According to the principle of isostasy, parts of the crust will rise or subside until these parts are buoyantly supported by their roots. As mountains rise above Earth s surface, deep roots form until isostatic equilibrium is achieved and the mountains are buoyantly supported.
Gravitational and seismic studies have detected thick roots of continental material that extend into the mantle below Earth s mountain range. Continents and mountains are said to float on the mantle because they are less dense than the underlying mantle and therefore project into the mantle to provide the necessary buoyant support. As peaks are eroded, mass decreases, and the roots become smaller. A balance between erosion and the decrease of the size of the root will continue until both the mountain and their roots disappear.
Isostatic rebound: is the slow process of the crust s rising as the result of the removal of overlying material. Seafloor structures, such as seamounts, must also be in isostatic equilibrium with the mantle. Elevation of Earth s crust depends upon the thickness of the crust as well as its density. Mountain roots can be many times as deep as a mountain is high (Mt Everest is 9 km above sea level and yet its crustal root is nearly 80 km thick).
Orogeny (ô-rŏj ǝ-nē): is the process cycle that forms all mountain ranges; orogeny results in broad, linear regions of deformation known as orogenic belts, most of which are associated with plate boundaries. Convergent boundaries are the location of the greatest variety and the tallest orogenic belts. The compressive forces at these boundaries may cause the folding, faulting, metamorphism, and igneous intrusions that are characteristic of orogenic belts. Interactions at each type of convergent boundary create different types of mountain ranges.
Oceanic-Oceanic Convergence When an oceanic plate converges with another oceanic plate, one plate descends into the mantle to create a subduction zone. As parts of the subducted plate melt, magma is forced upward to form a series of volcanic peaks called an island arc complex. Basaltic and andesitic magmas rise to the surface and erupt to form the island arc complex. Sediments around the complex can be uplifted, folded, faulted, and thrust against the island arc to form a mass of sedimentary and island-arc volcanic rocks.
Oceanic-Continental Convergence Convergence along oceanic-continental boundaries creates subduction zones and trenches. The edge of the continental plate is forced upward, marking the beginning of orogeny. Compressive forces may cause the continental crust to fold and thicken, as the crust thickens, higher and higher mountains form, and deep roots develop to support their mass. As the subducting plate sinks into the mantle, parts of the plate begin to melt, magma moves upward, giving rise to granitic intrusions and volcanoes fueled by andesitic magma. Sediment shoved against the continent form a jumble of folded, and faulted, and metamorphosed rocks.
Continental-Continental Convergence Because of the relatively low density of continental crust, the energy associated with a continental-continental collision is transferred to the crust involved. Compressional forces break the crust into thick slabs that are thrust onto each other along low-angle faults, possibly doubling the thickness of the deformed crust. The magma that forms as a result of continental-continental mountain building forms granite batholiths. Another common characteristic of mountains that form when two continents collide is the presence of marine sedimentary rock near the mountains summits.
The Appalachian Mountains A Case Study The geology of the Appalachian mountain range, which is located in the eastern United States, has been the subject of many studies. Geologists have divided the Appalachian Mountain Belt into several distinct regions, including the Valley and Ridge, the Blue Ridge, and the Piedmont Provinces. Each region is characterized by rocks that show different degrees of deformation.
The Early Appalachians About 700 to 800 million years ago, ancestral North America separated from ancestral Africa along two divergent boundaries to form two oceans with a continental fragment between them. The ancestral Atlantic Ocean was located off the western coast of ancestral Africa and a shallow, marginal sea formed along the eastern coast of ancestral North America. Similar rock types and geologic structures on different continents
The Early Appalachians 700 600 Million Years Before Present (M.Y.B.P.) Convergence causes the ancestral Atlantic Ocean to begin to close. An island arc develops east of ancestral North America. 600 400 M.Y.B.P. The continental fragment, which eventually becomes the Blue Ridge Province, becomes attached to ancestral North America.
The Final Stages of Formation 400-350 M.Y.B.P. The island arc becomes attached to ancestral North America and the continental fragment is thrust farther onto ancestral North America. The arc becomes the Piedmont Province. 350-270 M.Y.B.P. Ancestral Africa collides with ancestral North America to close the ancestral Atlantic Ocean. Compression forces the Blue Ridge and Piedmont rocks farther west, and the folded Valley and Ridge Province forms.
Beginning of the Pangaea Breakup 270-200 M.Y.B.P. Fragment of the African plate is left attached to North American plate as the two plates begin to move apart, creating the modern Atlantic Ocean. Looking closely at the middle of the Atlantic Ocean, one can see the mid-atlantic ridge creating new ocean seafloor.
Divergent-Boundary Mountains Ocean ridges are regions of very broad uplift that seems to be related to the rising convection cells in the mantle. Magma is less dense than surrounding mantle material, and thus it is forced upward, where it warms the overlying lithosphere. The lithosphere along a divergent boundary bulges upward to form a gently sloping mountain range
Ocean-Ridge Rocks Ocean ridges are composed mainly of igneous rocks. As tectonic plates separate along an ocean ridge, hot mantle material is forced upward and accumulates in a magma chamber beneath the ridge. From the chamber, the mixture intrudes into the overlying rock to form a series of vertical dikes that resemble a stack of index cards standing on edge. Pillow basalts are igneous rocks, resembling a pile of sandbags, that are formed when magma pushes through the dikes and erupts onto the seafloor.
Nonboundary Mountains Some mountains and peaks form in places far removed from tectonic boundaries. Three nonboundary types of mountains are uplifted mountains, fault-block mountains, and some volcanoes. Uplifted Mountains Uplifted mountains are mountains that form when large regions of Earth have been slowly forced upward as a unit.
Uplifted Mountains The cause of large-scale regional uplift is not understood. It is possible that warmer regions of the mantle heat portions of the lithosphere, causing the density of the crust to decrease, which results in slow uplift. Another possible cause is upward movement in the mantle, which lifts large regions of the crust without causing much deformation. The Adirondack Mountains in New York are an example of uplifted mountains.
Fault-Block Mountains Fault-block mountains form when large pieces of crust are tilted, uplifted, or dropped downward between large faults. The Basin and Range Province of the southwestern United States and northern Mexico, as well as the Grand Tetons in Wyoming, are examples of fault-block mountains.
Volcanic Peaks Volcanoes that form over hot spots are generally solitary peaks that form far from tectonic plate boundaries. The shield volcanoes that make up the state of Hawaii are volcanic peaks that formed as the Pacific Plate moved over a hot spot in the mantle.
J. Tuzo Wilson, Canadian Geophysicist In 1963, Canadian geophysicist J. Tuzo Wilson developed a concept crucial to the plate-tectonics theory. He suggested that the Hawaiian and other volcanic island chains may have formed due to the movement of a plate over a stationary "hotspot" in the mantle. This hypothesis eliminated an apparent contradiction to the plate-tectonics theory -- the occurrence of active volcanoes located many thousands of kilometers from the nearest plate boundary. Hundreds of subsequent studies have proven Wilson right. However, in the early 1960s, his idea was considered so radical that his "hotspot" manuscript was rejected by all the major international scientific journals. The manuscript ultimately was published in 1963 in a relatively obscure publication, the Canadian Journal of Physics, and became a milestone in plate tectonics. http://pubs.usgs.gov/gip/dynamic/wilson.html
All mountains are similar in that they tower high above the surrounding land. Some are formed along plate boundaries, while others form far from the boundaries. Some mountains are produced by faulting and folding; others form as a result of igneous activity and crustal uplift. No matter how they form, all mountains are evidence the Earth is truly a dynamic planet. Mt Shasta, Ca
Plate Interaction Diagram This image shows the three main types of plate boundaries: divergent, convergent, and transform. Image courtesy of the U.S. Geological Survey. http://oceanexplorer.noaa.gov/facts/plate-boundaries.html
Plate Interaction Diagram
Crust-Mantle Relationships Unit 5: Dynamic Earth Lesson 2d Mountain Building EEn 2.1.1 and 2.1.2 Section Assessment 1. What is isostatic rebound? Isostatic rebound is the slow process of the crust s rising as a result of the removal of overlying material.
Crust-Mantle Relationships Unit 5: Dynamic Earth Lesson 2d Mountain Building EEn 2.1.1 and 2.1.2 Section Assessment 2. What two elevation ranges, or modes, dominate Earth s topography? Most of Earth s elevations cluster around 0 to 1 km above sea level and 4 to 5 km below sea level.
Crust-Mantle Relationships Unit 5: Dynamic Earth Lesson 2d Mountain Building EEn 2.1.1 and 2.1.2 Section Assessment 3. Identify whether the following statements are true or false. false Peridotite is less dense than basalt. true Mountain roots can extend far deeper than the height of the mountain. true Buoyancy and gravity are the basic two forces in isostasy. false Oceanic crust, because it is denser, extends deeper into the mantle than continental crust.
Convergent-Boundary Mountains Unit 5: Dynamic Earth Lesson 2d Mountain Building EEn 2.1.1 and 2.1.2 Section Assessment 1. What is orogeny? The processes that form all mountain ranges are called orogeny.
Convergent-Boundary Mountains Unit 5: Dynamic Earth Lesson 2d Mountain Building EEn 2.1.1 and 2.1.2 Section Assessment 2. What is an orogenic belt? Where are most orogenic belts located? An orogenic belt is a broad, linear region of deformation associated with mountain building. Most orogenic belts are located along plate boundaries, particularly convergent boundaries.
Convergent-Boundary Mountains Unit 5: Dynamic Earth Lesson 2d Mountain Building EEn 2.1.1 and 2.1.2 Section Assessment 3. Identify whether the following statements are true or false. true The Philippine islands are an example of an island arc complex. false A subduction zone forms during a continentalcontinental collision. true The Blue Ridge province is the composed of the remnants of a continental fragment. true The modern Atlantic Ocean formed about 200 million years ago.
Other Types of Mountains Unit 5: Dynamic Earth Lesson 2d Mountain Building EEn 2.1.1 and 2.1.2 Section Assessment 1. Match the following mountain types with an example. A divergent-boundary D uplifted B fault-block C volcanic peaks A. ocean ridges B. Grand Tetons in Wyoming C. Mauna Kea in Hawaii D. Adirondacks in New York
Other Types of Mountains Unit 5: Dynamic Earth Lesson 2d Mountain Building EEn 2.1.1 and 2.1.2 Section Assessment 2. What are pillow basalts? Pillow basalts are igneous rocks, resembling a pile of sandbags, that are formed when magma pushes through the dikes and erupts onto the seafloor.
Other Types of Mountains Unit 5: Dynamic Earth Lesson 2d Mountain Building EEn 2.1.1 and 2.1.2 Section Assessment 3. How do fault-block mountains form? Fault-block mountains form when large pieces of crust are tilted, uplifted, or dropped downward between large faults.
Chapter Assessment Unit 5: Dynamic Earth Lesson 2d Mountain Building EEn 2.1.1 and 2.1.2 Multiple Choice 1. A mountain s root as mass is removed from the mountain through erosion. a. expands c. rises b. sinks d. melts Buoyant force will cause the root of the mountain to rise, maintaining isostatic equilibrium.
Multiple Choice Chapter Assessment 2. When did the tectonic history of the Appalachian Mountains begin? a. 700 600 M.Y.B.P. c. 400 300 M.Y.B.P. b. 500 400 M.Y.B.P. d. 300 260 M.Y.B.P. The Appalachians are one of the oldest surviving mountain chains on Earth and have been the subject of numerous studies.
Multiple Choice Chapter Assessment 3. Which type of convergence could create a mountain that has marine sedimentary rock near its summit? a. oceanic-oceanic c. continentalcontinental b. oceanic-continental d. none of the above Continental-continental convergence thrusts thick slabs onto each other to form mountains. Some of the crust that is thrust upward may be made of marine sedimentary rock, such as the case of K2 in the western Himalayas.
Multiple Choice Chapter Assessment 4. What is the average elevation of exposed land in relation to sea level? a. 364 m c. 841 m b. 562 m d. 1257 m Two elevations dominate Earth s surface: 0 to 1 km above sea level and 4 to 5 km below sea level. The average elevation above sea level is 841 m and the average depth of Earth s oceans if 3865 m.
Multiple Choice Chapter Assessment 5. The processes that form all mountain ranges are called. a. convergence c. uplift b. divergence d. orogeny Convergence, divergence, and uplift are all types of orogeny.
Short Answer Chapter Assessment 6. How large is a mountain s root in relation to the mountain? A mountain s root can be many times larger than the mountain itself. It is estimated that the root under Mount Everest extends over 80 km into the mantle.
Short Answer Chapter Assessment 7. Isostasy involves the equalization of what two forces? The two forces at work in isostasy are buoyancy and gravity.
True or False Chapter Assessment 8. Identify whether the following statements are true or false. true As a mountain erodes, it rises. false Warmer regions of the mantle may be responsible for uplifted mountains. false The Hawaiian islands formed along a divergent boundary. true The piedmont is the remnants of an ancient island arc. true Continental crust extends deeper into the mantle than oceanic crust.
Section 20.1 Study Guide Unit 5: Dynamic Earth Lesson 2d Mountain Building EEn 2.1.1 and 2.1.2 Section 20.1 Main Ideas Earth s elevations cluster around two intervals: 0 to 1 km above sea level and 4 to 5 km below sea level. These modes reflect the differences in density and thickness of the crust. Isostasy is a condition of equilibrium. According to this principle, the mass of a mountain above Earth s surface is supported by a root that projects into the mantle. The root provides buoyancy for the massive mountain. The addition of mass to Earth s crust depresses the crust; the removal of mass from the crust causes the crust to rebound in a process called isostatic rebound.
Section 20.2 Study Guide Unit 5: Dynamic Earth Lesson 2d Mountain Building EEn 2.1.1 and 2.1.2 Section 20.2 Main Ideas Orogeny is the cycle of processes that form mountain belts. Most mountain belts are associated with plate boundaries. Island arc complexes are volcanic mountains that form as a result of the convergence of two oceanic plates. Highly deformed mountains with deep roots may form as a result of the convergence of an oceanic plate and a continental plate. Earth s tallest mountains form along continental-continental plate boundaries, where the energy of the collision causes extensive deformation of the rocks involved. The Appalachian Mountains, which are located in the eastern United States, formed millions of years ago mainly as the result of convergence between two tectonic plates.
Section 20.3 Study Guide Unit 5: Dynamic Earth Lesson 2d Mountain Building EEn 2.1.1 and 2.1.2 Section 20.3 Main Ideas At a divergent boundary, newly formed lithosphere moves away from the central rift, cools, contracts, and becomes more dense to create a broad, gently sloping mountain range called an ocean ridge. Rocks that make up ocean ridges include dikes and pillow basalts. Regional uplift can result in the formation of uplifted mountains that are made of nearly horizontal, undeformed layers of rock. Fault-block mountains form when large pieces of the crust are tilted, uplifted, or dropped downward between normal faults. Most solitary volcanic peaks form as a tectonic plate moves over a hot spot in Earth s mantle.