Earth’s continents are large land areas extending from high mountaintops to sea level. The oldest continental rocks are billions of years old, so the continents have had a lot of time for constructive and destructive forces to change them. Constructive forces cause physical features on Earth’s surface, known as landforms, to build up. Destructive forces cause physical features to wear down. Landforms often build up when Earth’s crust deforms. This occurs when slabs of crust compress, pull apart, or slide past other slabs of crust. Crust deformation can result in the formation of hills,... Show more Earth’s continents are large land areas extending from high mountaintops to sea level. The oldest continental rocks are billions of years old, so the continents have had a lot of time for constructive and destructive forces to change them. Constructive forces cause physical features on Earth’s surface, known as landforms, to build up. Destructive forces cause physical features to wear down. Landforms often build up when Earth’s crust deforms. This occurs when slabs of crust compress, pull apart, or slide past other slabs of crust. Crust deformation can result in the formation of hills, valleys, and other landforms. Mountains rise when continents collide and push up the crust. Volcanic mountains form when a slab of oceanic crust plunges beneath another slab of crust. This allows melted rock called magma to flow onto the surface, where it hardens to form solid rock. Over time, the hardened rock builds up to form a mountain. Landforms are also created when sediments are deposited. For example, a triangular deposit called a delta forms where a river or stream deposits sediments as it flows into a body of still water. Volcanic eruptions are constructive forces when they cause mountains to form. However, explosive volcanic eruptions can be destructive forces if they blow apart mountains, leaving craters. Landforms are also worn down by the destructive forces of weathering and erosion. Water, wind, ice, and gravity are important agents of erosion. For Show less
Earth’s continents are large land areas extending from high mountaintops to sea level. The oldest continental rocks are billions of years old, so the continents have had a lot of time for constructive and destructive forces to change them. Constructive forces cause physical features on Earth’s surface, known as landforms, to build up. Destructive forces cause physical features to wear down. Landforms often build up when Earth’s crust deforms. This occurs when slabs of crust compress, pull apart, or slide past other slabs of crust. Crust deformation can result in the formation of hills, valleys, and other landforms. Mountains rise when continents collide and push up the crust. Volcanic mountains form when a slab of oceanic crust plunges beneath another slab of crust. This allows melted rock called magma to flow onto the surface, where it hardens to form solid rock. Over time, the hardened rock builds up to form a mountain. Landforms are also created when sediments are deposited. For example, a triangular deposit called a delta forms where a river or stream deposits sediments as it flows into a body of still water. Volcanic eruptions are constructive forces when they cause mountains to form. However, explosive volcanic eruptions can be destructive forces if they blow apart mountains, leaving craters. Landforms are also worn down by the destructive forces of weathering and erosion. Water, wind, ice, and gravity are important agents of erosion. For
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