Types of Boundaries PDF

SES4U​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Name: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Date: Types of Boundaries By the end of this lesson, I will be able to e...

SES4U​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Name: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Date: Types of Boundaries By the end of this lesson, I will be able to explain how plates can interact and subsequently, what physical phenomena will result Seafloor Spreading American scientist, Harry Hess, compiled the topographic, sediment age and thickness, and magnetic data mentioned previously and proposed a single theory that could explain them all. His theory is called Seafloor Spreading and states that new ocean crust is being created along ocean ridges and destroyed along deep-sea trenches. To understand how this works one must first be aware that Earth’s crust and rigid upper mantle are broken into enormous ‘slabs’ called plates. These plates move at different rates and in different directions. This motion is believed to be the result of convection currents. (Hot magma from Earth’s interior rises, cools and sinks again creating large circular movements in the mantle. The moving mantle drags the plates along with them.) Along ocean ridges, plates are being pulled apart. As a result, magma rises to fill the gap forming new seafloor as it cools and crystallizes. Ocean trenches are formed where plates collide. One of the two colliding plates is subducted; it is forced downward beneath the other plate. When this happens, the subducted plate is melted, and the seafloor is destroyed. This seafloor spreading provides answers to the two questions plaguing Wegener’s continental drift hypothesis. Mantle convection provided the force that moves the continents. The continents are not plowing through the seafloor. Instead, they are merely passengers that ride with the plates as they slowly move away from the ridges (or spread). Plate Boundaries The places that plates interact (like ocean ridges and trenches) are called plate boundaries. There are three basic types of plate boundaries. Each type of boundary has certain geological characteristics and processes associated with it. SES4U​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Name: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Date: 1) Diverging Plate Boundaries Like those found at ocean ridges, diverging plate boundaries occur where tectonic plates are being pulled apart. These are almost all found below the ocean waters along the seafloor. It is here that seafloor spreading begins. The only place where this can be found to happen on land is in Iceland. Volcanism and earthquakes are associated with these boundaries. 2) Converging Plate Boundaries Like those found along a deep-sea trench, converging plate boundaries occur where plates are colliding. There are three distinct kinds of converging plate boundaries. ​ Oceanic-Oceanic converging plate boundaries result in one of the two oceanic plates being subducted. These form deep sea trenches. The subducted plate melts and this hot magma rises often creating an arc of volcanic islands that run parallel to the trench ​ Oceanic-Continental converging plate boundaries also lead to subduction. The denser oceanic crust always sinks beneath the less dense continental crust. Once again, the subducted plate melts and magma rises. This time, however, the result is a chain of volcanic mountains along the edge of the continent forming mountain ranges. SES4U​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Name: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Date: ​ Continental-Continental converging plate boundaries occur when two colliding continental plates sandwich an ocean basin. The ocean basin is entirely subducted, while the colliding edges of the two continental plates crumple and uplift forming mountain ranges. Because neither plate is subducted, these boundaries produce the highest mountain ranges. 3) Transform Boundaries These are regions where two plates are moving horizontally past one another. As the two plates slide past each other the crust is deformed or fractured. This often results in earthquakes. SES4U​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Name: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Date: Practice! 1.​ What type of boundary is found at each of the following sites? a.​ San Andreas Fault b.​ Mid-Atlantic Ridge c.​ Andes Mountains d.​ Mariana Trench e.​ Aleutian Islands off the coast of Alaska