Unit 2: Surface Processes and the Hydrosphere Lesson 6: Processes and Features of Erosion (Heath Earth Science – Pg. 190-202)

Today’s Objectives Relate the processes associated with weathering and erosion to the resulting features, including: identify the processes (e.g., abrasion, dissolution) by which glaciers, running water, wind, and wave action erode rock and sediment differentiate between erosional and depositional features formed by glaciers, running water, wind, and wave action

Types of Erosion Erosion can be carried out in many different ways Today we will look at 4 different processes of erosion: 1) Glacial Erosion 2) Running Water Erosion 3) Wind Erosion 4) Wave Erosion In addition to looking at these processes, we will also identify some features created by erosion, as well as features formed by deposition

Erosional vs. Depositional The incorporation and transportation of material by a mobile agent, such as water, wind, or ice Deposition: The process by which materials are added to a landform after being transported by a mobile agent

Glaciers – Chapter 11 A glacier is a thick mass of ice originating on land from the compaction of snow that shows evidence of flow Two main kinds of glacier: Valley glacier (alpine glacier) Occur in all parts of the world where mountains stretch above the snow line 2000-100,000 meters long, 100-1000 meters thick Continental glacier (ice sheet or ice cap) Occur in polar areas where the snow line is close to sea level Up to 12.5 million km2, up to 5 km thick! Glacier Simulation

Advancing vs. Receding Glaciers Accumulation zone: Area of glacier where accumulation > melting Ablation zone: Area of glacier where melting > accumulation Firn (snow) line: line where melting = accumulation When the amount of snow falling in the accumulation zone is larger than the amount of snow melting in the ablation zone, the glacier will advance When the opposite is true, the glacier will recede Advancing glaciers will create erosional features Receding glaciers will create depositional features

Glacial Erosion - Abrasion Glaciers erode the bedrock largely by using pieces of rock as cutting tools These pieces are dragged over the bedrock by the forward movement of the glacier, in a process called abrasion The scratches left behind on the rocks are called striations

Glacial Erosion - Plucking Another process of glacial erosion is plucking Plucking occurs when melt-water beneath the glacier penetrates cracks in the bedrock, then freezes to the rock (video) As the glacier moves forward, the rock is pulled from the ground

Glacial Erosional Features You should be able to name and recognize the following erosional features, and how they are formed: arete, cirque, horn, hanging valley, U-shaped valley, roches moutonnees, fjord, tarn

Glacial Erosional Features

Glacial Deposition Once a glacier begins to recede, the material from beneath, within, or on top of the glacier will be left behind This material will form many features called depositional features You should be able to name and recognize the following depositional features, and how they are formed: Till, moraine, outwash plain, drumlins, eskers, kames, kettles, and erratics

Glacial Depositional Features

Glacial Depositional Landforms

Homework Complete the homework package that you are given! Due: Next class Next day: We will continue discussing erosion and erosional/depositional landforms Soon: Unit Test!

Running Water Erosion – Chapter 10 Another agent of erosion is running water Running water transports sediment in three ways: Solution Suspension Bed load

Running Water Erosion Solution: Suspension: Material that has dissolved from the bedrock are carried in solution Minerals such as calcium and magnesium are often carried in solution Suspension: When a river looks muddy, it is carrying material in suspension Suspended material includes clay, silt, and fine sand Are kept from sinking because of turbulence Faster moving water can keep more material in suspension

Running Water Erosion Bed load: Sand, pebbles, and boulders that are too heavy to be transported in suspension may be moved along the stream bed Very common during floods Boulders and pebbles roll or slide along the riverbed Sand grains jump and bounce along the bottom Sediment moved along the stream bed is called the bed load

Running Water - Abrasion Much like in glaciers, weathering and erosion by running water also involves abrasion: Sand, pebbles, and even boulders carried as load in the water will grind and hammer away at its bed Over time, this abrasion causes rock to be worn down and rounded: this rock is known as river rock

Erosional Features – V-shaped Valleys Running water wears away and erodes the surface, of mountains they flow down creating river valleys River valleys are typically V-shaped: High speed water easily scours away the streambed Upper valley walls are widened by weathering and erosion

River Valley Drainage Patterns Topography influences the shape of the rivers drainage system

Erosional Features - Potholes Streams running over irregular beds develop small circular currents called whirlpools As whirlpools develop, sand, pebbles, and small boulders abrade the streambed, grinding out deep oval or circular holes called potholes

Depositional Features – Oxbow Lakes Mature river valleys develop wider floors Rivers are easily deflected from side to side, forming meanders As a meander gets larger and larger, the curve can become a loop and break through its bank This is called a cutoff Result is an abandoned meander, or oxbow lake

Depositional Features – Oxbow Lakes

Depositional Features - Levees In times of heavy rain, rivers may overflow their banks and cover part of the valley floor This part of the valley floor is called the flood plain As water flows over the river bank, it slows down and releases some of its sediment load Largest, heaviest sediment is released first Finer sediment released last This larger sediment forms a “wall” or levee on each river bank, a natural form of flood protection

Depositional Features - Levees

Depositional Features - Deltas When a river meets the sea, or a lake, the velocity of the water slows down dramatically As it slows, the fine sediment in the suspended load will be deposited at the mouth of the river, forming a delta

Depositional Features – Alluvial Fans Similar to a delta, but occur in dry regions where a steep mountain stream meets flat, dry land at the bottom of the mountain Again, water velocity slows down greatly, sediment load is dropped forming a fan-shaped deposit, called an alluvial fan Different from a delta in that: 1) formed on land, not in water 2) sediment is coarse sand and gravel instead of fine sediment 3) surface is sloping, not flat

Depositional Features – Alluvial Fans

Homework You should be able to identify and explain the following erosional/depositional features formed by running water: delta, alluvial fan, oxbow lake, pothole, levee, v- shaped valley

Wind Erosion – Chapter 12 Another agent of erosion is wind Just like running water and ice, abrasion is a process of wind based weathering and erosion High winds pick up sand particles, which grind away at rock features the wind blows into

Erosional Features - Ventifacts Boulders and rocks that have been shaped by sand blasting winds, are called ventifacts Have one or more sides that have been worn away by sand blasting

Wind Erosion Another effect of wind erosion is deflation Deflation describes the removal of loose rock particles by wind Usually sand, silt and clay will be blown away first, leaving behind pebbles and boulders Material carried away by wind and deposited elsewhere is called loess Such a surface is known as desert pavement The heavy surface material of desert pavement protects the material beneath from further deflation

Erosional Features – Desert pavement

Erosional Features - Blowouts In some areas where larger materials are not present, blowouts are common A blowout is a hollow resulting from the removal of huge amounts of soil due to deflation

Depositional Features - Dunes Hills of sand deposited by wind are called dunes, or sand dunes Dunes form when deposited sand piles up against shrubs, boulders, or other obstructions Found wherever there are strong winds and enough loose sand If wind blows steadily from one direction: Dunes have long, gentle slope on windward side Short, steep slope on the leeward side Dunes occur in many different shapes, dependent on the amount of sand available, strength and steadiness of winds, and amount of vegetation present

Depositional Features – Dunes Pg. 213-214

Wind Depositional Features - Crossbedding Over time, winds can change direction, reversing direction of the dunes As older dunes get buried, pressure builds turning them into stone This process creates another feature, called crossbedding

Homework You should be able to identify and explain the following erosional/depositional features formed by wind: dunes, cross-bedding, blowouts, desert pavement, ventifacts

Wave Erosion – Chapter 12 One last agent of erosion is wave action Waves repeatedly pounding against the coast, along with abrasion, can create numerous erosional and depositional landforms

Anatomy of a Wave Wave height is the difference between its high point (crest), and its low point (trough) Wavelength is the distance from one crest to the next The period of a wave is the amount of time it takes one wavelength to pass a given point Almost all waves are generated by wind

Erosional Processes – Longshore drift As waves strike the coast at an angle, sediment is picked up at an angle, then dropped as the water follows gravity back to the ocean This causes sediment to migrate down the coast, a process called longshore drift

Erosional Features – Sea Stacks and Sea Arches

Erosional Features – River rocks, Undercutting

Wave Depositional Features Homework: You should be able to recognize and explain the following erosional and depositional features created by wave action: Sea arch, sea stack, tombolo, spit, beach, sandbar