Earthquakes Volcanoes Mountains Sea Floor Spreading Where is it located? How does it form? How does it change the Earth s surface?
Earthquakes Where are earthquakes located? Most earthquakes happen around the edges of the Pacific Ocean or near mountainous areas such as the Himalayas. Earthquakes, like volcanoes are found along the edges of the Earth s plates. How does an earthquake form? Earthquakes happen where two of the Earth s plates meet, or collide. The constant pressure of the plates pushing against each sometimes builds to a breaking point, when one snaps, and suddenly causes the ground to move forward. Shock waves from this ground movement cause the earth to shake, or quake. The ground shakes violently and huge cracks may appear. An earthquake begins beneath the ground at the point where rocks move. The movement creates waves of energy which travel up to the surface. Transcurrent Fault Profile of an earthquake The point where the earthquake begins underground is called the focus. The point on the surface above the focus is called the epicenter. There may be lots more minor earthquakes called aftershocks after the first earthquake. How do earthquakes change the Earth s surface? Earthquakes may cause structures such as buildings and bridges to fall. They can also trigger mudslides and avalanches. Earthquakes in the ocean can cause giant waves or Tsunamis to crash in to the shore, changing the shoreline.
Volcanoes Where are volcanoes located? Volcanoes occur where hot liquid reaches the surface through cracks in the Earth s crust. Most volcanoes are found where two plates are pushing against one another or moving apart. Volcanoes that erupt are called active. Many of them are found in areas around the Pacific Ocean called the Pacific Ring of Fire. How does a volcano form? Pressure builds up underground and pushes molten liquid rock up from a chamber beneath the surface. It spews out of a crack in the ground as lava. How do volcanoes change the Earth s surface? Eruptions can cause lateral blasts, lava flows, hot ash flows, mudslides, avalanches, falling ash and floods. Volcano eruptions have been known to knock down entire forests. An erupting volcano can trigger tsunamis, flashfloods, earthquakes, mudflows and rock falls. More than 80 percent of the earth s surface is volcanic in origin. The sea floor and some mountains were formed by countless volcanic eruptions. Gaseous emissions from volcanoes formed the earth s atmosphere.
Mountains Where are mountains located? Mountains are rock masses that are at least 2,000 feet high. They are found all over the world. They cover about one quarter of the Earth s land surface. With the exception of a few isolated peaks, most of the Earth s mountains are part of mountain ranges. How does a mountain form? There are four different types of mountains. Each one is formed in a different way. Fold They are formed when two plates collide head on, and their edges crumbled, much the same way as a piece of paper folds when pushed together. Fault Block They are formed when the faults move some blocks of rock up while others are moved down. Volcanic A volcanic grows when lava dust and ashes gradually builds in a cone shape. Dome Mountain Dome type mountains are made when hot magma rises up from deep in the Earth and pushes the rocks above into a dome shape. How do mountains change the Earth s surface? Mountain belts that are adjacent to active, convergent plate boundaries are still growing, as evidenced by active volcanoes, frequent earthquakes, and measurable changes in elevation. Geologic features such as folds, faults, and igneous rocks remain in place long after the period of active mountain building that formed them has ended. How are mountains formed, and what is the connection with earthquakes? The answer may lie in the fluid-like properties of the Earth s outer layers. According to a new theory, mountains may flow up or down when continents collide, in the process; they affect the circulation of the planet s atmosphere and change the climate.
Sea Floor Spreading Where is the location of sea floor spreading? The Earth s crust is made up of plates. Both the continents and ocean floors move as part of these plates. Most plates move apart beneath the oceans. Usually, in the ocean the floor is moving in different directions in different places. How does sea floor spreading happen? During ocean-floor spreading, hot magma from the mantle fueled by convection currents, pushes up through the cracks between the oceanic plates. As the molten rock comes up, it spreads. Then it cools and fills in the gap between existing plates. The cooled rock will later be forced to spread apart by new magma forcing its way upward. How does sea floor spreading change the Earth s surface? Where sea floor spreading is happening, a mountain range forms underwater. This is because the Earth s plates are pulling apart. The build-up of new plate material forms underwater ridges along the boundaries of the plates. A mountain range like this runs down the middle of the Atlantic Ocean and is called the Mid-Atlantic Ridge.