Earth Science- Chapter 4

Earth Science- Chapter 4

Weathering- when rocks are broken down because of physical or chemical changes.
1. Physical weathering- what is physical weathering? The rock will be broken down into smaller pieces or a different shape but there will be no change in its chemical composition.
A few natural ways a rock can be broken down:
a. Frost action- water seeps into the rock thru the cracks, then the water freezes and expands in the cracks and it causes the crack to get larger and the rock expands to accommodate the larger water. When the weather warms up, the ice will melt. The water will evaporate, and the rock is left with large cracks. This cycle will happen over and over again and the cracks will grow larger and larger until the rock splits.
b. Plant roots- happens because of the roots of the plants. The roots reach into the soil and the roots expand as the plant gets bigger. If it finds its way into the cracks of a rock, as the roots expand, they’ll push the rock apart.
c. Animals- when the animals dig into the ground, they bring new rocks up to the surface and these rocks are now exposed to different factors that can cause them to weather.
d. Abrasion- when things knock into each other.
1. When a stream is flowing and with in it there are rocks and some rocks knock against others and knock into the water all. All the collision causes the rocks to break.
2. Wind blows little pieces of rock against exposed rock surfaces and there is a collision and eventually the rock will crack.
3. Moving ice scrapes against the rock, causing the rock to break.
4. Wave action- waves of the sea attack rocks on the shore and cause them to break down.
5. The force of gravity could cause breakage.
From all the weathering we see that some rocks are soft and some are hard- some break easier than others.
a. Quartz- is made of silica. It’s a hard rock that resists physical weathering.
b. Mica- soft rock that breaks easily.
2. Chemical weathering- changes the mineral composition of the rock and forms a completely new substance.
Deep in the crust of the earth there isn’t really and chemical weathering. When rock comes to the surface, it’s exposed to the hydrosphere and atmosphere and chemical weathering can occur.
2 things that speed up chemical weathering:
a. Rain
b. Heat
c. Acid- acid rain is regular rain that absorbed carbon dioxide and pollution Ex. Sulfur and nitrogen absorb organic acid making the rain acid rain. If this acid rain comes in contact with rock, the rock will decompose. Ex. If limestone is combined with acid, chemical weathering will occur.

Examples of chemical weathering:
a. Iron+ oxygen= iron oxide (rust)
b. Feldspar- when exposed to oxygen and water, chemical weathering will occur, and it’ll become clay.
c. Olivine-located deep in the ground. If exposed, it will become clay.

Soil-

What is soil made up of?
1. Weathered rocks
2. Micro-organisms
3. Organic remains
4. Bedrock

Different types of soils are effected by:
1. Climate- the type of climate is going to affect the soil because it’ll affect the amount of moisture in the soil, the amount of air in the soil, and the amount of organic matter in the soil.
2. What the rock is made up of and how much weathering the rocks went through- physical weathering is going to determine the size of the rock fragments. When some rocks undergo chemical weathering, they turn into clay. The amount of clay in the soil is going to be soft or hard depending on the rock pieces inside the soil. If there is a lot of organic matter in the soil, the organic matter is going to decompose. When organic matter decomposes, it produces organic acid. The more organic acid there is, the more chemical weathering there will be.
If there are a lot of animals in the area, the animals are going to bring rocks up to the surface. When rocks are exposed, more weathering can happen. A lot of animals= more organic matter (wastes).

Formation of soil- (Layers of soil are aka soil horizons)
1. Residual soil- soil that rests on top of its original bedrock. All residual soil is going to have 4 layers:
a. There’s bedrock.
b. Broken bedrock- formed from weathered bedrock.
c. Mineral enriched horizon- water with a lot of soil because the ground water hash infiltrated this layer and produced minerals.
d. Humus- dark, black soil, which is full of organic matter. The more organic matter there is, the more fertile the soil is going to be.
2. Transported soil- top layer of soil was brought to another location. This soil won’t have all the layers.
Transported soil moves through the process of erosion- transportation of sediments (rock fragments) from one location to another. There are many ways erosion can happen:
a. Erosion through gravity
b. Erosion by water
c. Wind erosion

Erosion-
1. Erosion through gravity- when gravity moves something from 1 area to another without the help of wind, rain or ice. When this happens, it’s called a mass movement/ mass wasting. The rocks are going to slide, flow or fall down.
It’s more probable that erosion by gravity is going to happen if:
a. There is water within the sediment.
b. There’s freezing and thawing within the rocks.
Examples of erosion by gravity:
a. Landslide
b. Fallen rocks
c. Slow creep
d. Slumping
2. Erosion by water- if there’s a moist place, erosion will probably be erosion by water. There’s a stream flowing and it carries rock sediment with the water. Depending on the size and density of the rock, we can determine what kind of erosion is going to take place:
a. Solution- very small rock particles are going to be carried along the river in solution. These rocks are so small that they can’t be filtered out of the water naturally.
b. Suspension- small particles that won’t settle on the river floor on their own. They are large enough to be filtered out of the water naturally.
c. Floatation- the lightest particles with the lowest density float along the surface of the river. Very often, these are composed of organic matter and they are very light.
d. Traction- heaviest and largest sediments are rolled along the river floor by traction.
Stream velocity- the speed of the stream. Different stream velocities will move along different sized sediments. In order for traction to occur, stream velocity has to be very high. By looking at the size of sediments in a stream, the velocity can be determined.
What effects velocity?
a. Gradient
b. Discharge- amount of water in the stream. The more water, the faster the velocity. The greater the velocity, the more erosion is going to happen. The speed of the stream is a balance between the pull of gravity and friction. The center of the stream has the least friction, so it moves the fastest. There is even friction between the stream and the air.
There are some rivers that have S shaped curves- the river meanders. When the river passes along the curve, it goes very quickly along the outside of the bend. As it passes along the outside of the S, there’s greater erosion. Because the water is going slowly on the inside of the s, there will be deposition.
3. Wind erosion- the wind picks up sediments of rocks and carries them from one place to another, for example clay, sand and silt. Erosion by wind happens in a place where the soil is loose and there are no plants holding the soil down.
4. Erosion by ice- ice transfers sediment from one area to another by glaciers. Glaciers are large blocks of slow moving ice. Glaciers form in a very cold area- the Arctic areas.
How do glaciers form? When the snow piles up faster then it melts, the bottom layer of snow forms into a block of ice.
When the glacier movers, it acts as an abrasion system, causing rocks that it passes along to break or get scratched. Sometimes, a glacier will smooth out the side of a mountain.
Different types of glaciers form different landscapes:
a. Continental glaciers- a glacier that covers a very large area. As it passes over the land, it’s going to deepen and widen valleys and it’s going to grind down any hills in the area. With it it takes along sediment.
b. Valley glacier- it scours rocks away in order to create a U shaped valley with the sides of the mountain almost vertical. Valley glaciers move very slowly. The ice in the center of the glacier moves the fastest.

Identifying agents of erosion- what agent of erosion caused this erosion to look this way?
1. A rough, angular rock- gravity.
2. Round, smooth rock- eroded by water.
3. Rounded and striated rock- eroded by glaciers.
4. Ventifacts (rock that’s angular with facets)- eroded by wind.
5. Talus- angular and rough- eroded by gravity.

Deposition- when sediments are deposited in an area. Aka sedimentation.

What effects deposition?
1. Particle size-
a. Larger particles are deposited first.
b. Small particles are deposited slower.
c. Tiny particles won’t settle unless the solution its in is saturated. Ex. The Persian Gulf has lots of salt. When the weather gets hot, the water evaporates and the Persian Gulf is as saturated with salt as it can be. If more water would evaporate, the water would be oversaturated with salt. The salt will begin to settle and it will crystallize. These salt crystals are called precipitates. The process of the salt crystallizing is called precipitation.
2. Particle shape- the more friction there is between the particle and water, the longer it will take to settle.
a. A flat, angular particle with an irregular shape will take a long time for deposition to occur.
b. A smooth, round rock will be dropped off quicker.
3. Density of the particle- if the size and the shape are the same, the denser particle will be deposited first.
4. Speed of the agents (things that cause deposition)- wind, ice, gravity… If any of the agents are moving quickly, deposition won’t be happening so much. As the agent slows down, deposition is going to increase. Ex. as a stream enters an ocean, it slows down, and deposition will occur.

Sorting of sediments- deposited according to size, shape and density. Sometimes, sediments aren’t deposited according to size, shape and density, for example if wind stops blowing, if it goes according to size, shape and density, it’s called sorting of sediments.
1. Horizontal sorting- near ocean shoreline. First large rocks are deposited, then medium rocks. As the agent of deposition slows down, the rocks will get smaller and smaller.
2. Vertical sorting- as the river slows down, deposition will increase. The smaller rocks will settle on top of the larger rocks.
3. Graded bedding- a few layers of sorting one on top of the other and every layer represents a different event. This usually happens in vertical sorting. Ex. There is a lake at the foot of a mountain. The mountain has a landslide, and all the rocks that tumble down sort on the bottom of the lake. This event happens year after year. Eventually, there will be many layers of sorting on top of each other.

Types of deposition-
1. Deposition by gravity- when it occurs, the sediments aren’t sorted. Rocks fall off a cliff and form one pile of angular, unsorted rocks.
2. Deposition by water- when you look at sediments inside a stream, you can see how fast the stream is going. When the stream is going slow, there will be lots of deposition. In a very slow part of a river, it may have to be dredged (cleaned) because there are so many rocks. As the river enters the ocean, it deposits the sediments in a delta shape.
3. Deposition by wind- sediments carried by the wind. These sediments are fine because the wind can carry heavy sediments. Sometimes, the wind blows the sediment into hills known as dunes. Sand is blown up on the windward side and deposited on the leeward side. This usually happens at the beach or in the desert.
Cross bedding- wind blows the sand into different layers that meet at different angles.
Most deposition in a desert doesn’t come from wind, but rather from flash floods- thunderstorms that occur suddenly and infrequently.
4. Deposition by glaciers- sediments can be deposited by moving ice or by the melted water, and a bunch of unsorted rocks will be left.
Erratic- deposition that occurs by ice. Large boulders are deposited above a stream valley. They are rounded and striated. That that they are high and striated is proof that this deposition occurred by glaciers and not by water.
5. Deposition by melt water- when a glacier melts, the sediments inside the glacier are released and deposited.

NY and the Ice Age- how was NY affected by erosion and deposition of glaciers?
1. When the ice formed- in the N Pole, a big block of ice began to flow to NY. Depending on how much snow gathered with this glacier, it could flow a few cm a day, or a few meters a day.
2. As the glacier flows along, it’s going to cause erosion:
a. Alpine/Valley glaciers- as they flow along, they create a U shaped valley. U shaped valleys in NY were formed by these glaciers.
b. Continental glaciers/ice sheets- also creates landscapes.
c. A glacier causes erosion by smoothing out the rocks- a glacial polish.
3. Deposition by glaciers- the Finger Lakes in NY were formed by deposition.
a. As a glacier moves, it deposits unsorted sediments (aka till).
b. As the ice moves along, it pushes soil and rock in front of it. Eventually, the glacier slides over the pile of soil and rock, creating a drumlin- tear shaped hill. The round part of the tear drop faces the direction that the glacier came from.
c. When the ice stops moving S, it leaves piles of unsorted sediments that are called moraines.
Proof that there are moraines:
1. Long Island is an island that has 2 long fingers poking out that were formed by moraines.
2. There’s a valley that stops the Finger Lakes from continuing onward. This valley was formed by a moraine.
4. Kettle/kettle lakes- when a glacier inside the ground melts, kettle lakes are formed. When the water evaporates, a dry depression known as a kettle is left.

Path of NY glacier- starts from the N pole and moves S. As it goes S, it begins melting. When it moves forward at the same rate that it melts, it’s standing still- at a dynamic equilibrium. When it’s melting quicker than it’s moving, it’s in essence retreating.


How are oceans and coasts affected by deposition and erosion?
1. Oceans- 71% of earth’s surfaces are covered by oceans. The deepest part of the ocean is one mile deeper than Mt. Everest.
A lot of sediments that are deposited on earth will eventually be brought to the ocean and be deposited there. Proof- most fossils are marine fossils.
It is very common for sediments to be deposited in the ocean through salt. A lot of different elements can be mixed into pure salt and brought into the ocean with salt. When there is too much salt in the ocean, it crystallizes on the ocean floor and will eventually turn into sedimentary rocks.
2. Coast- there are 2 ways for erosion and deposition to occur along the coast:
a. Long shore currents- currents that flow along near the shore and cause erosion along the shore.
b. Waves- flow of energy through water. As the waves get closer to the shoreline, they get narrow and tall. The surface water along the waves are moving in ellipses which get smaller and smaller as you get deeper into the ocean.
As a wave gets closer to the shore, there’s an increase in friction because more ocean water is touching the ocean floor. This friction slows down the waves. The other waves catch up and build on top of the original waves, making them taller. When the waves get too tall, they break and crash onto the shore. At this point, a lot of energy is released.
How does this energy effect erosion?
1. Because of the friction that the waves create within the sediment- the energy causes the molecules in the rock to rub against each other until there is so much friction and the rocks break.
2. The energy moves sand from one area of the shoreline to another in the zone of longshore transport. Within this zone, the sand is being moved back and forth.
3. Energy builds shoreline features:
a. Sand bars- ridges that are submerged and run parallel to the shore.
b. Sandspits- long ridges of sand that extend into the mouth of the bay.
c. Baymouth bars- sand bar that blocks the mouth of the bay.
d. Barrier islands- islands made of sand.
e. Wave-cut cliff- cliffs that face the sea along the shore.
f. Marine terrace- a wave-cut platform that is exposed above sea level.
g. Sea arch- an arch formed when two sea cave unite through erosion.
h. Sea stack- when a sea arch crumbles.
There are some people who decided that we must protect the shore because there is so much erosion going on and soon there’ll be no shore left. They built structures:
1. Breakwater- to stop the waves.
2. Seawall- to stop the waves.
3. Jetties- to hold the sand in place.
4. Groins- to hold the sand in place.
After these structures were put into place, the people began to notice that less erosion was happening at one area, but more erosion was happening at another area, so the people decided to leave nature alone.

Landscapes- general shape of the region of the land.

Landscapes are formed by:
1. Landforms- rocks that have the same age and composition.
a. Hills
b. Streams
c. Valleys
2. Topography- shape of the land.

3 major landscapes:
1. Mountains- has the greatest topographic relief (difference between elevations) of all landscapes. Mountains are made up of the greatest variety of rocks. Forces within the earth push up land to form mountains. Mountains have high gradient streams- steep streams. The steeper the river, the quicker the river. Because they go very fast, they cause a lot of erosion.
2. Plateau- the top of the plateau is generally flat. Sometimes plateaus will have rolling hills. Plateaus can have streams. If there are streams on the plateau, there will be a deep valley. A plateau is formed from layers of sedimentary rocks piled one on top of the other. A plateau has a smaller topographic relief than a mountain.
3. Plains- has no elevation above sea level. A plain has the smallest topographic relief. Plains are generally flat, but could have hills. Plains are made up of layers of sedimentary rocks.

Landscape region- a specific area that has a landscape. It can be general or more specific.

Things that affect landscape:
1. Climate- more rain or less rain is going to effect how the landscape looks.
a. Moist, humid climate-
1. Fertile soil
2. Full streams. There isn’t a lot of erosion though because the vegetation holds down the soil.
3. Hills have rounded slopes because of all the rainfall.
b. Arid, dry climate-
1. Thin soil
2. A lot of physical weathering especially in the winter when there is a lot of frost action.
3. Because there is so much physical weathering, the particles are angular and rough.
4. The soil has very big pores so the rain infiltrates quickly and deeply. Therefore, only certain desert plants can survive in this climate because there are very big breaks between rainfalls. When it does rain, there are flash floods. A lot of erosion occurs because there isn’t enough vegetation to hold the sand down.
5. Most streams are dry except when it rains.
3. Geological factors- types of rocks earth is made up of. Even in the same climate, different areas have different landscapes because they are made up of different rocks.
a. Durable rocks- rocks that are and hard. These rocks didn’t have so much physical weathering. If there are durable rocks in the area, mountains, plateaus and escarpments (cliffs) are formed.
b. Soft rocks- can be broken down easily. Streams can run through them and form valleys. They form low areas because the soft rock could be eroded very easily. Soft rocks form smooth hills.
c. Mixed- the landscape is going to have a stepped appearance.