Earth’s Surface J.Quigley 4/2013

Earth’s Surface

How would you describe Earth’s surface? Would you mention mountains, valleys, cities and farms? Most people would describe the landscape…. What covers most of the surface of earth??

Earth’s Surface WATER!

Earth’s Surface 71% of Earth is covered in Water Earth is sometimes called the “water planet” For billions of years the presence of water has shaped the geology and biology of Earth’s surface

Earth’s Surface The temperature range on earth allows water to occur in three states: – Liquid- water – Solid-ice – Gas-steam/vapor

Earth’s Surface Most of the earth’s water is salt water found in oceans Only about 3% of the earth is fresh water Most of this fresh water occurs in the form of ice and snow The liquid fresh water is usually found underground

Earth’s Surface Groundwater- the liquid fresh water found under the ground A smaller amount of liquid fresh water is found in lakes, rivers and streams and as water vapor or in clouds in the atmosphere

Water Cycle Water moves among the oceans, atmosphere and land in a cycle that covers the entire surface of the earth and even extends below the ground The continuous movement of water is called the water cycle.

Water Cycle The water cycle is made up of several processes including evaporation, transpiration, condensation, precipitation and the eventual return of flowing water to the ocean The energy of sunlight and the force of gravity power the water cycle

Water Cycle

Evaporation- liquid water to water vapor. Solar energy causes water on earth surface to evaporate Sunlight heats water and causes it to change into water vapor in the air The warm, moist air expands and rises, carrying the water vapor higher into the atmosphere

Water Cycle Most evaporation happens over the ocean and large lakes Some water vapor enters the atmosphere when it is released from the leaves of plants in a process called transpiration

Water Cycle Condensation- a gas (water vapor) to a liquid Water vapor does not stay in the atmosphere for long. As warm air rises, it expands and cools. Because the colder air holds less water vapor than warm air, condensation occurs

Water Cycle In condensation, water vapor forms droplets on small particles in the air. At lower temperatures, ice crystals form Billions of these droplets or ice crystals make up clouds…

Water Cycle Precipitation- When the water droplets or ice crystals in clouds get too heavy, gravity causes them to fall to the ground as precipitation – Rain – Snow – Sleet – Hail – Freezing rain

Water Cycle Precipitation-

Water Cycle A single molecule of water will move between the surface of the earth at the atmosphere many times. About 90% of the water that evaporates from oceans falls back into the oceans Most of the water that falls on land quickly turns back into vapor The remaining water seeps into the soil to become ground water or glaciers.

Fresh Water

Fresh water – water that is free of minerals and salts Only a small portion of water on Earth is fresh water. A small portion of the Earth’s fresh water is located in the atmosphere, streams and lakes. Most is located in ground water and glaciers

Fresh Water The atmosphere- A small percentage of the earth’s fresh water is found in the atmosphere in the form of water vapor or clouds Water enters the atmosphere by evaporation and transpiration

Streams and Rivers Streams and Rivers contain even less fresh water than the atmosphere. Streams and Rivers are very important in shaping the surface of the land

Streams and Rivers When rain falls on land, much of it enters the ground, but some becomes runoff. Runoff is water that flows over the Earth’s surface

Streams and Rivers A stream is any natural channel of flowing water. Streams flow together to form a network called a river system. River systems resemble a tree.

Streams and Rivers A major river has many smaller streams, called tributaries, that flow into it. Tributaries collect runoff from the surrounding land and channel it into rivers.

Streams and Rivers The area of land that contributes water to a river system is called a watershed. Watersheds, also called drainage basins, can be small or large. The Mississippi River watershed drains most of the central United States!

Ponds and Lakes Ponds and Lakes form in depressions in the land. Lakes form in large, deep depressions Ponds form in smaller depressions and tend to be smaller and shallower than lakes Both ponds and lakes usually drain into streams.

Water Beneath the Surface About ¼ of all freshwater is groundwater. Close to the surface, the pore spaces in rock and soil are filled with air Deeper below the surface is the saturated zone, a region where pore spaces are entirely filled with ground water

Water Beneath the Surface The top of the saturated zone is called the water table. The shape of the water table is usually similar to the ground surface above it Lakes and streams are usually found below the water table

Water Beneath the Surface Water flows more easily through some rocks than others. A rock is permeable if water can easily pass through it. – Sandstone – Limestones

Water Beneath the Surface A permeable rock layer that is saturated with water is called an aquifer Many parts of the world rely on aquifers as a source of water for drinking and agriculture.

Water Beneath the Surface Rocks are impermeable if water cannot easily pass through them. Shale and unbroken granite are example of impermeable rock In places where impermeable rock layer is exposed, water may seep to the surface.

Glaciers and Icebergs Glaciers form in areas where more snow falls than melts each year As snow builds up, the weight of the snow presses on the layers below, changing them into ice When the weight of snow is great enough, glaciers begin to flow slowly down hill Ice is added at the top of the glacier through snowfall Ice is removed from the glacier by melting, sublimation and the formation of icebergs

Glaciers and Icebergs

An iceberg are a large piece of ice that breaks off when a glacier reaches the ocean Many icebergs drift great distances from glaciers each year They can be hazardous to ships and ocean drilling platforms Glaciers eventually melt as they float into warmer waters.

Glaciers and Icebergs

Weathering and Mass Movement Look at the picture of the Grand Canyon… Its shape, texture, depth… All of this was formed by the river at the bottom of the canyon, over millions of years!

Weathering and Mass Movement Erosion- the process that wears down and carries away rock and soil Erosion created the Grand Canyon Erosion acts through weathering, the force of gravity and through the movement of streams, groundwater, glaciers, wind and waves. Overtime erosion breaks down even the tallest mountains… the end product of erosion is sediment

Weathering and Mass Movement Weathering- is the process by which rocks are chemically altered or physically broken down into fragments at or near the earth’s surface There are two forms of weathering- mechanical and chemical

Weathering and Mass Movement Mechanical weathering- the process of physically breaking rock into smaller fragments Mechanical weathering occurs through frost wedging, abrasion, growth of plant roots and other processes

Weathering and Mass Movement Frost wedging is the most common form of mechanical weathering… when water freezes to form ice, the water expands. This expansion pries open any cracks the water has seeped into.

Weathering and Mass Movement Abrasion- Another form of mechanical weathering where rocks scrape and grind against one another. Abrasion occurs when sand carried by water or wind causes bits of rick to break off as if they were being sandblasted.

Weathering and Mass Movement Plant roots- roots grow into cracks in a rock. Roots exert a powerful force that can slowly pry the rock apart.

Weathering and Mass Movement Chemical weathering- a process in which rock is broken down by chemical reactions. Chemical weathering involves chemical reactions that dissolve the minerals making up the rock or change them into new minerals

Weathering and Mass Movement Water is the main agent of chemical weathering. Water is a very effective solvent (it dissolves many things) Rusting is another example of chemical weathering…

Rates of Weathering The rate at which mechanical and chemical weathering take place depends on three main factors: – Temperature – Availability of water – Type of rock

Weathering and Mass Movement Mass movement is the downward movement of rock and soil due to gravity. Through the process of mass movement, gravity moves loose materials down a slope There are four main types of mass movement: – Landslides – Mudflows – Creep – Slumping

Weathering and Mass Movement Landslides- the rapid movement of large amounts of rock and soil. Landslides often occur after heavy rains or after an earthquake loosens soil Landslides that occur on the sides of mountains can destroy entire towns!

Weathering and Mass Movement Mudflows- rapid mass movements of soil and other sediment mixed with water. Mudflows tends to occur in areas where fine sediments has collected in thick layers. When it rains, water loosens the sediment that has collected into thick layers. After a heavy rainfall the mud then flows down the slope

Weathering and Mass Movement Creep- Occurs when soil gradually moves down a slope. Creep often occurs because of the formation of ice Each time the ground freezes, the soil expands outward When the ground thaws, the soil moves a small distance downhill It is a very slow process and takes long periods of time to notice the ground movement

Weathering and Mass Movement Slumping- Occurs when weak layers of rock or soil suddenly move downslope as a single unit. Gravity acting on water- saturated soil and rocks causes slumping Slumping often leaves a curved shape “scar” in the hillside.