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Science Study Guide
Slow Changes on Earth, Chapter 5
Fourth Grade
Vocabulary
Word Definition Example bay A body of water that is partly enclosed by land and has a wide opening delta A large mass of sediment deposited at the out of a river deposition The dropping of sediment moved by water, wind, and ice The movement of rock material from one place to another A single large boulder moved by a glacier and deposited when the glacier melts erosion erratic glacier A large mass of slow moving ice headland A point of land, usually high, that extends out into the water Word Definition Example moraine A long ridge formed by boulders, rocks, and soil carried and deposited by a glacier river system The largest river and all the waterways that drain into it A hill or pile of sand that was formed by the wind The slow wearing away of rock into smaller pieces sand dune weathering Lesson One
What Are Weathering
and Erosion?
Weathering
The slow wearing away of rock into smaller pieces Causes of Weathering Ice Plant Roots Moving Water Most rocks have tiny cracks in them. When rainwater enters the cracks and freezes the cracks expand and over time causes the rocks to break. When plant roots grow into the cracks in a rock, the growing root widen the cracks, and the rock breaks. Streams flow over rocks, moving them. Over and over rocks bump against other rocks. As the rocks wear down, sharp edges become smooth and the rocks get smaller. Chemicals Gases sin the air react with rainwater to form acid rain. Acid rain weakens rock, causing it to break apart. Erosion
The movement of rock material from one place to another • Water is the main cause of erosion • Weathering and erosion take place over thousands and even millions of years A drop of water spalshes into the soil The water loosens and picks up Gny parGcles When the water moves downhill, it carries the Gny parGcles with it As water flows ove the soil it picks up more parGcles Over many years, the running water carries enough weathered material away to form a deep canyon Glacier
A large mass of slow-­‐
moving ice • Movement is so slow that it is difficult to see • As it moves it causes both weathering and erosion • Can form valleys and canyons Lesson Two
How Does Water Shape the Land?
• Water wear away and reshapes rock • Water moves pebbles, sand, and soil from one place to another Deposition…The dropping of sediment moved by water, wind and ice Changing Coastline Ocean Waves and Currents Move sand along the shore Headland •
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Seasons Winter Months Strong winds during the winter In summer, gentle waves deposit months produce strong waves that more sand on the beaches that remove more sand from the shore they remove. This widens the than they deposit. This narrows beach. the beach. A point of land, usually high, that extends out into the water. A headland is surrounded by water on three sides Bay • A body of water that is partly enclosed by land • Has a wide opening, called the mouth • The mouth connects the bay to the ocean Seasons Summer Months River Systems The largest river and all the waterways that drain into it. Deposition creates a variety of land surface features. Delta A large mass of sediment deposited at the mouth of a river Alluvial Fan A fan shaped land mass that forms after a river rushes down a steep slope and slows over a flat plain Meanders As a river flows over flat land, the river tends to wind in curves. People Shape the Land People can shape the land by building dams on rivers • Dams create large reservoirs • Dams change the natural flow of the water in rivers • Dams keep sediments from flowing down river Affects of Dams • Provide irrigation water • Provide electricity • Provide recreational opportunities Floodplain The land where a river tends to flood. Lesson Three
How do Ice and Wind Shape the Land?
Glaciers • Large mass of slow moving ice that flows down a slope • As is moves, it is a great force of erosion • As glaciers melt they leave behind a changed landscape What Glaciers Leave Behind Moraine The long ridge formed by boulders, rocks and soil carried and deposited by a glacier Cirque A bowl shaped hollow left by a glacier Erratic A single large boulder moved by a glacier and deposited when the glacier melts Evidence of Glaciers
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Glaciers formed nearly all the lakes in Yosemite Valley Glaciers have helped shaped mountains Glaciers have carved valleys Glaciers left depressions that became lakes Grooves As a glacier moves, rocks embedded in the ice scratch across rocks lying under the ice. Large grooves left in the underlying rock can show the direction the glacier moved. Wind Carves the Land Wind can change the shape of land • Wind easily picks up and carries beach and desert sand • Wind is more likely to cause erosion during a dry period • Sediments that wind carries also weather the Earth’s surface Wind Builds Up the Land
Wind picks up sediment from one place and deposits it in another place The place where the sediment is deposited is then built up Sand Dune • A hill or pile of sand that was formed by the wind • Sand Dunes vary in size • Sand Dunes can move depending on how strong the winds are Dust Bowl Poor farming practices and years of not rain destroyed the ground cover. Without these plants, the soil was not held in place. Wind-­‐blown soil covered everything.