Water and Climate

 

We already know that all weather on Earth depends on the amount of water available in an area. We will soon see that the amount of water in an area will determine an area’s climate. The amount of water that exists on Earth is constant. There is the same amount of water today as there was when water first formed the oceans. 70% of the surface is covered in water. Yet, there are different forms that water takes. All the forms that water takes make up the water cycle. Another term for the water cycle is the hydrologic cycle. Salt water comprises 97.2 % of all water, while fresh water comprises 2.8% of all water. All life (for the most part) depends on that small portion of water. The fresh water is found mostly in ice caps and glaciers (2.2%). Some is in the atmosphere as water vapor (0.0001%), some as surface water (0.02%), and the rest as ground water (ca. 0.6%).

 Water first formed about 4 billion years ago, when Earth’s atmosphere cooled and formed free oxygen that bonded with hydrogen. Once water formed, Earth began recycling water in the water cycle. This cycle depends on insolation to drive it. Insolation evaporates a great deal of ocean water to form precipitation that returns water to the surface. What are the stages of the water cycle?

1)      Evapotranspiration – the changing of liquid water to water vapor.

2)      Condensation – the changing of water vapor to liquid water.

3)      Precipitation – the falling of water to Earth.

Once the water strikes the surface, one of four things happens.

1)      Water retention – water stays on the surface for periods of time as snow or ice.

2)      Infiltration – water enters the ground to become ground water.

3)      Runoff – water runs along the ground back to bodies of water.

4)      Evapotranspiration all over again.

Different places on Earth have different amounts of water. Deserts have very little water while tropical areas have much water. The amount of water in an area can be illustrated by a water budget, which is similar to a monetary budget. When an area receives the same amount of water as it evaporates, the area is in equilibrium. When an area receives more water than it evaporates, the area has a surplus of water. When an area receives less water than it evaporates, it has a water deficit. Which areas have water surpluses and which have water deficits?

 

 Between today and tomorrow we will analyze what factors will cause infiltration and which cause runoff. Let’s start with infiltration.

 Seven factors affect infiltration.

1)      Slope of the land – the flatter the land is, the more infiltration will occur because the water just sits there. If the slope increases, runoff occurs. Therefore, the greatest amount of runoff would be at a 90 degree angle (a cliff).

2)      Degree of saturation – the drier the land is, the more infiltration will occur because the land is parched and has room between the soil particles to enter the ground. If water is already present, there will be less infiltration occurring.

3)      Porosity – the space between soil particles. If an area has a ground made up of pebbles and rocks as well as dirt, space exists between particles; thus, the ground is porous. If a place is paved, there is no space between particles; thus, the area is non-porous. Porosity depends upon three factors:

a)      Shape – if particles are rounded, space is created between them, allowing infiltration. If particles are not rounded, less space exists because the particles actually touch each other. This allows for very little infiltration.

b)      Packing – the closer the particles are to each other, the less infiltration will occur because there is less space. This can be when people walk on snow, crushing the particles together.

c)      Sorting - if all particles are the same size, infiltration is the greatest. If the particles are different sizes, the smaller particles will fill the spaces between the larger ones, reducing infiltration.

4)      Permeability – some rocks are capable of allowing water to pass through them. These rocks are permeable. If rocks are permeable, infiltration will occur. If a rock is impermeable, no infiltration will occur.

5)      Capillarity – some rocks retain a film of water around their edges because they attract water molecules in much the same way that plant roots allow water to travel up the plant stems.  This is capillarity. If an area has capillarity, more space exists for infiltration. If there is no capillarity, infiltration will be less. Capillarity allows water to leave the ground, making room for water to enter the ground.

6)      Vegetation – if an area has vegetation, it will create more capillarity, increasing the amount of infiltration in the area.

7)      Land use – in unpaved areas infiltration is greater than in paved areas for reasons already discussed.

Infiltration will lead to the creation of the water table. We will look at this tomorrow.

 

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Yesterday we saw factors that affect infiltration. Where does the water go once it is absorbed by the ground? It becomes groundwater beneath us. We saw that 0.6% of all water exists in the form of groundwater. Where is groundwater? It exists at a depth where water carves a passage through rock. The rock that is carved depends on its composition and resistance to weathering. Since all locations have different rocks, the depth at which the groundwater exists varies. The depth at which groundwater exists is called the water table. The water table has different sections.

 

1)      Zone of saturation – the deepest part of the water table. The ground here is always saturated. Plant roots do not absorb water from here.

2)      Capillary fringe – rocks here are always covered by water because the rocks sit on top of the zone of saturation. The water leaves the rocks as liquid. This is the water table. This is the location where well water comes from. However, this water has so many different dissolved minerals inside that it is best to boil the water first.

3)      Zone of aeration – the top of the water table. It is not saturated and is the area where most infiltration occurs. If this is filled with water, runoff will occur.

 

 There are two types of wells. An ordinary well is one that is dug by people through rock to the depth of the water table. It must be deep enough down that it will almost touch the zone of saturation so that water is present at dry times. Otherwise, it dries up. The second well is natural. It is an artesian well, or artesian formation. Impermeable rock like shale sits above permeable rock that has eroded away. The water is trapped underground. If we drill through the rock, the water spurts out with great force. This is the artesian well. This is how oil is brought to the surface.

 

 If water is not infiltrated, it runs off. There are several factors that will affect runoff. These factors are:

 

1)      Rate of precipitation – if precipitation is faster than infiltration, runoff occurs.

2)      Pore space of rock – if the pores are small, very little infiltration will occur, and runoff will increase.

3)      Slope of land – if it is great, runoff exceeds infiltration.

4)      Surface water – if it has not evaporated, runoff will occur.

 

 Most runoff takes the water back to streams and oceans. This is important for the water cycle. More runoff means that more water will sit in a stream bed. This affects the stream discharge in a given area. Stream discharge is the volume of water passing a certain point at a certain time. It is expressed as cubic meters per second or liters per minute. When this happens, flooding can occur. Flooding can also result from storms, saturated land, high tides, or other means. Higher ground is safest. Topographic maps help governments determine where higher ground is for coastal communities.

 

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We already saw how water is unevenly distributed through Earth and we already saw how coastal areas have a shorter temperature range than inland areas. Therefore, locations along major bodies of water would have varying weather conditions when compared to inland locations. We further analyzed oceans and how they affect weather because of their different currents. The different types of weather conditions for coastal areas compared to inland areas is called climate. Climate is the overall weather picture of an area for a period of time (usually 30 years). Temperature and moisture conditions are the two main aspects of climate.

 Temperature determines climate in two ways: the yearly range of temperature from high to low and the monthly range of temperature from high to low. This monthly range is the annual temperature range and is calculated by taking the average of the hottest month and the average of the coldest month and subtracting the two averages.

 Arid climates are those climates with very little rainfall, while humid climates are those climates with a great deal of moisture. Arid climates have much more evapotranspiration than precipitation. Humid climates have much more precipitation than evapotranspira-tion.

 

 There are eight factors that affect climate. These factors are:

1)      Latitude – the higher the latitude is, the lower the temperature is. Therefore, colder climates exist as you approach the poles than by the Equator. Insolation varies with latitude; therefore, the amount of evapotranspiration will vary with latitude. Generally, less evapotranspiration occurs in colder climates than in warmer climates. Climates near the poles experience large temperature ranges through the year than those areas near the Equator. Latitude is also going to affect the moisture conditions in an area. Remember the planetary wind and pressure belts? These separate humid climates from arid climates. We will investigate this in Lab next week.

2)      Oceans and large bodies of water – areas near a large body of water are regulated by the difference in specific heat of the water body and the land mass on which it sits. This results in low temperature ranges as opposed to inland where temperature ranges are severe. The bigger the landmass is and the further away from a body of water a location is, the bigger the temperature difference will be.

3)      Planetary wind and pressure belts – the prevailing winds in an area will drive the different air masses that form and thus will affect an area. Warm air masses and cold air masses will affect the climate of an area. Monsoons are related here for reasons already discussed earlier in the year. These wind patterns will drive moisture through an area.

4)      Ocean currents – warm ocean currents bring warm air from the Equator to cooler environments while cold ocean currents drive cooler air from the poles to the Equator. The warm air allows for more evaporation, which would cool when approaching cool areas, condense and cause increased precipitation.

5)      Elevation – higher altitudes will produce cooler temperatures because warm air is condensing as it rises. Higher altitudes have fewer greenhouse gases, which produce lower temperatures. The decrease in temperature results in more precipitation than lower altitudes.

6)      Mountains – when air reaches a mountain, it is forced to climb, condense and precipitate on the windward side of the mountain (the side that faces the wind). The air then is cooler, sinks, and expands, but is drier because all moisture has been left on the other side of the mountain. This is the leeward side of the mountain, and is the sight of many deserts.

7)      Vegetation – the more trees in an area will produce more infiltration and will convert solar energy to food. When we chop down trees, we discontinue infiltration because the roots have disappeared. The solar energy in the area is used to heat up the land instead of to make food. Therefore, deforestation and urbanization raise temperatures.

8)      Cloud cover – the more clouds in an area will result in more reflection of sunlight while fewer clouds result in more absorption of sunlight. For this reason, the Equator (which is very stormy) is cooler than desert areas (which are dry).

 

 Because there are changes in the amount of insolation in areas, temperatures will vary. These temperature differences will affect wind patterns in the oceans, particularly the Pacific Ocean. Winds change direction when upwelling produces warmer temperatures than normal. This is a monsoon condition. We call it el Nino. Temperatures are more erratic than normal.

 

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We have already illustrated the water cycle and saw how water is unevenly distributed around the globe. Now we will see how even in the hydrosphere (the realm of earth with water) is different. Not every ocean is the same. Each ocean has different amounts of salt. Salt water is water, salt, and other substances. Some oceans have more salt than others. The more salt in the body of water, the higher its density is because there is more solid material present. This is one difference between the world’s oceans.

 Oceans differ by their floor features as well. The ocean floor has abyssal plains (flat areas along the center of the floor), abyssal hills (small mounds along the floor at varying distances), continental rise (collection of sediment at the base of the continent), continental slope (the very edge of the continent), and continental shelf (flat part of the continent on which we stand at the beach). These features are along a passive continental margin – one where no plate activities occur (like the Atlantic Ocean). An active continental margin (one with plate activities like the Pacific Ocean) also has trenches. More on this when we do plate tectonics.

 The last difference between the oceans are ocean currents. Looking at the Earth Science Reference Tables, we see warm and cool ocean currents. Name some of each. Warm currents bring warm air to cool places while cool currents bring cool air to warm places. Density currents are movements of water that occur when extremely salty water meets les salty water. The saltier water sinks to the bottom because of its higher density while less salty water floats due to its low density. Upwelling occurs when cold ocean floor water rises to the surface to replace warm water pushed out by the wind.

 

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------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------                                                       Weathering, Erosion, and Deposition

 

We have already studied meteorology and climate. We know that some climates are very moist while others are very dry. We also know that some climates vary greatly in temperature. These different climates play a role in the breakdown of rocks. The particles that form from the breakdown of rock are called sediments. The process of breaking down rocks at or neat the Earth’s surface is called weathering. Weathering affects construction projects because the size of the particles will determine if something can be used as a foundation for a building or not. There are two types of weathering – physical weathering and chemical weathering. Each type has several forms.

 

 Physical weathering is the breakdown of rock by physical forces. There are three kinds of physical forces –abrasion, plants, or frost action (ice wedging). When rocks move against each other (such as when wind blows sediments against one another), they rub against each other, forming smaller particles. This is called abrasion. Sometimes small plants called lichens grow on rocks. Their roots stretch into the veins of rocks and break the rock open. This is physical weathering by plants. In New York City and other middle latitude locations extreme temperature changes are common. In winter temperatures drop, allowing water to freeze. When water enters small cracks in rocks or streets, it freezes and expands. When temperatures climb, the water thaws, melts and contracts. This process of repeated freezing and melting produces larger and larger cracks. This is called ice wedging, or frost action. This is how potholes form.

 

 Chemical weathering is the breakdown of rock by chemical processes. There are several forms of chemical weathering. An example is oxidation, which is the rusting of iron products due to exposure to oxygen in the atmosphere. The by product of oxidation is iron oxide. Another example is the dissolution of substances in water. Water is the universal solvent because almost everything dissolves in water. The last example is carbonic acid. Through carbonic action, rocks such as limestone and marble dissolve because the minerals inside disappear with the acid.

 

 What are the factors that determine the rate of weathering?

1)      Exposure – the closer the rock is to the surface, the faster it will weather because most weathering agents are near the surface.

2)      Particle size – the smaller the particle is, the faster it will weather because the surface area is larger. You can have the same amount of mass in three different sizes of the same substance. The smallest sized particles would weather the fastest.

3)      Mineral composition – the type of mineral in the rock determines how quickly or slowly weathering occurs because certain minerals (halite/calcite) dissolve faster than others (quartz/metals).

4)      Climate – the more humid the climate is and the hotter the climate is, the faster weathering will occur. Water is present in the environment that weathers particles and hot temperatures lead to more energy for weathering.

 

The breakdown of rock leads to the formation of soil. Soil is the by product of weathering. A soil profile is helpful in determining how long weathering has been occurring in an environment. Some profiles are more mature than others. The pieces of a soil profile are:

1)      Horizon A – topsoil. This is the mature soil profile. It consists of plant material, humus, and some small particles.

2)      Horizon B – subsoil. This is soil that has not been fully weathered yet. It contains sediment but not much organic material.

3)      Horizon C – partly weathered rock. The rock is being weathered but has a while to go yet.

4)      Horizon D – unweathered rock. This is rock that has not started to weather yet.

 

See notes for diagrams.

 

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Erosion is the transport of sediment that has been formed by weathering. Erosion is responsible for shaping and leveling the surface. If sediments do not match the rocks upon which they lay, erosion was responsible for transporting them there. All erosion depends upon three components: an agent of erosion (mass movement, people, wind, glacier, or stream), sediments, and force. Waves and currents are also responsible for erosion, but could be associated with wind and water. Gravity is the force for all erosion. Erosion is continuous because plate movements consistently raise the surface while erosion consistently levels the surface. Solar energy and insolation fuel the erosional system that drives wind and precipitation.

 When erosion occurs, it is only natural for sediments to drop somewhere. The dropping of sediments is called deposition. The type of deposition is dependent on the agent of erosion that has occurred. There is sorted and unsorted deposition. Certain erosional agents create sorted deposition – same size or layered – while others create unsorted deposition – no order whatsoever. Deposition depends on four factors.

1)      Size – smaller particles take more time to settle than larger ones because smaller particles are light weight and can move with wind.

2)      Shape – round particles settle fastest because they are equally exposed to friction on all sides. Think about a paper ball versus a sheet of paper dropped from the same height at the same time.

3)      Density – more dense settles fastest than less dense. Look over everything we have said about density thus far.

4)      Saturation of dissolved minerals – when a body of water is saturated with dissolved material, the dissolved material might fall out of the water and form rock.

Deposition also depends on the speed of the agent. The agent must slow down to deposit sediment. More on this later.

 

 Gravitational erosion is called mass movements. There are several mass movements possible. Some are fast and some are slow. All mass movements have gravity pulling rocks downward while friction with the surface holds everything in place. When gravity overwhelms friction, objects fall down. When heavy rains flood an area, friction is reduced greatly, and mudslides may result. If rocks are knocked loose by vibrations, rock falls result. If snow and ice are knocked loose by vibrations, avalanches result. When soil sits on a slope, it moves downhill very slowly. This is soil creep. Construction, quakes, eruptions, or storms could trigger mass movements. All mass movements are fast, except soil creep. The Earth Science Reference Tables show that a large speed is needed to move large particles while small speeds are needed to move small particles. Since mass movements are fast, mass movements result in unsorted deposits. There is no pattern to deposition here.

 

 People create construction, which produces unsorted deposition due to the machinery. We transport particles from place to place. Enough said.

 

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We have analyzed mass movements and people, and we have seen how each of them has caused erosion. Now we will look at wind as an agent of erosion and the features carved by wind. Wind moves slowly most of the time. Looking at the Earth Science Reference Tables, we see that most particles moved by wind are sand, silt, and clay. These particles are the smallest substances on Earth. Rarely will pebbles be moved by wind. Wind erosion occurs mostly in deserts or on beaches. Wind erosion creates two distinct features – deflation, and sandblasting (abrasion). When wind blows, it moves small particles with it. These particles slam into rocks in the area. Where the particles strike the rocks, abrasion occurs. Small pieces of the rock are carved out and moved by the wind. Generally, the bases of the rocks are targeted by wind erosion because the particles are not light enough to suspend themselves any higher. As a result of abrasion, mushroom rocks form, much like the ones that fall on Wile E. Coyote. This is similar to the process used to clean bricks. In areas where loose sediment is to be found, wind moves the loose sediment over great areas. The areas where the sediment abandoned become deflated, or lower in elevation. Deflation continues until desert pavement is formed. Desert pavement is composed of larger particles not able to be moved by wind.

 Wind only transports small particles – sand, silt, and clay. Silt and clay are referred to as dust because they are so small. When wind slows down, it deposits these sediments. These particles are deposited over large areas of land or water. They add to the surface4 of the environment. The sediments deposited by sand are collected in mounds called sand dunes. The dunes have a gentle slope facing the wind because the wind picks up sediment on the windward side and transports it to the other side where it is deposited. The leeward side faces against the wind and is steep because sediment is dumped there. There are four types of sand dunes – barchan, transverse, longitudinal, and parabolic. Barchan dunes form when sediment moves in the direction of the wind and forms a mound. These are crescent shaped, generally. Transverse dunes are really barchan dunes that have been lined up perpendicular to the wind, but the sediment is now being blown over the new windward side. Longitudinal dunes are very long dunes that lie parallel to the wind. Parabolic dunes are high dunes in the shape of a horseshoe that has a pan of sand that has accumulated around plant roots or rocks. The rest of the dune is crescent shaped and face the wind. These are barchans with a collection of sand some distance away. Over time sand dunes migrate. Wind constantly blows the sediment over great distances, moving the dunes.

 Wind transfers energy to waves and currents, setting these in motion. Therefore, it should come as no surprise that waves and currents are related to wind erosion. As waves approach shore, their bottoms hit shallow first, producing circular motions that drive the energy to the top of the wave. The top of the wave continues to move until its weight can no longer support itself, and it crashes to the beach. The force with which the wave slaps the shore erodes sediment already there. The waves that slap the shore are breaking waves, or surf. The energy that is released from a breaking wave is intense, and shapes the shoreline. If the shoreline is bent, the waves refract as they reach shore. This refraction allows the waves to strike shore at an angle. The waves remove loose sediment, carving the shoreline features that we see by satellite. Straight shorelines are pounded evenly throughout because no refraction has occurred. Water near the shore pushes in one direction as a result of the angle that waves strike the shore. This push generates a current called the longshore current because it moves parallel to the shore. Sediments trapped between the waves striking at an angle and the longshore current move in zigzag direction up and down the coast until they are deposited in shallow water. Over time, these deposits may form a sandbar, which is a collection of sediment that juts out of the water. At low tide sandbars are exposed, but in high tide they may be covered by water. The new body of water between the sandbar and shore is calm. We call this body of water a lagoon. There are several types of sandbars:

1)      Hook – rounded sandbar

2)      Barrier islands – series of sandbars

3)      Spit – sandbar connected to land at two ends

4)      Baymouth bar – connected to land at one end

Sediment may pile up along the shore when low tide occurs. The difference between high tide and low tide in an area is called a beach. This is sandy. The sediments here are rounded and smooth because of constant abrasion. Sandbars collect much more sediment than areas without sandbars because water slows down and deposits more material. These piles may be eroded over time by storms.

 

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A glacier is a naturally formed mass of ice and snow located in the coldest environments on Earth. There are two types of glaciers – continental glaciers are ice sheets covering Antarctica, Greenland, and northern portions of Canada, Russia, Siberia, and Scandinavia while valley glaciers are sheets of ice and snow located on top of the world’s tallest mountains. Not every mountain has a valley glacier because the temperatures on the mountain tops warm above the freezing mark, melting the glaciers. The elevation where the temperature lingers between above and below freezing is called the snow line because above this elevation temperatures are freezing and form ice while temperatures below are above freezing and ice melts. At different times of the year the snow line shifts with the differences in InSolAtion. All glaciers start out as firn, which is the granular snow that falls and sticks to the ground. As more and more firn collects, the sheet of snow and ice accumulates, forming a glacier. Glaciers always move downhill because of gravity. This movement will erode the area because of the friction. Certain features are formed as a result of this movement.

 Glacial movement depends on the ever shifting temperatures. As temperatures warm up, snow and ice melts, giving the appearance that the glacier retreats while falling temperatures allow the glacier to move forward. Be clear that the appearance of glacial movement is all apparent. Glaciers only move forward, NEVER BACKWARD. However, the rate between melting and freezing will determine whether the glacier appears to move forward, backward, or not at all. Glaciers move forward when they accumulate more frozen material than they melt away. Glaciers retreat when they melt more material than they accumulate. Glaciers do not move at all when they melt material at the same rate that they accumulate it.

 At the very front of the glacier is the ice front. This is what advances, retreats, or sits still. The distance that a glacier moves depends upon the rate of freezing/melting. However, keep this in mind. There is always friction between the sides of a glacier and the walls of the valley that it carves as well as between the bottom of the glacier and the floor that it carves. Therefore, the sides and bottom of a glacier move more slowly than the top and middle of a glacier. That is why snow an dice move to the front of a glacier and why the middle of a glacier sticks out further than the sides. Since glaciers carve the sides of a valley evenly all around, they form U-shaped valleys. This is important to keep in mind. Glaciers are frozen masses and carry anything as they move. Because of this, when a glacier melts, it dumps everything it carried at the front. This is unsorted material. It is not unusual for glaciers to have carried boulders from one area and deposit them in one another. In fact, Long Island has boulders that did not form here but were dropped off here by glaciers. When boulders do not match the composition of the land, we call them erratics.

 How do glaciers erode the land? As glaciers move, they drag rock and other frozen material along the floor and sides of valleys. Sometimes these materials stick out of the glacier. When this happens, they scratch the floor and sides. These are glacial scratches. They are parallel to the floor and sides, so they are glacial parallel scratches. When these materials cut holes in the floor and sides, we call them glacial grooves. The direction of the grooves and scratches determines the direction of the glacier. You can recognize material eroded by glaciers because they have some rounded edges to them and they contain scratches and grooves in them.

 We can spot glacial erosion atop mountains by looking at the peaks. Glaciers move rock from the top of a mountain downhill. Therefore, the top becomes rounded. Glaciers dig out rock from the floors, forming holes in the floors. These holes can fill with water later and become kettle lakes. When glaciers carve mountain sides, they carve away the side of the mountain, forming a cirque, which is a semi-circular hole in the side of a mountain. When two cirques are side by side on the same peak, they are called an arête. When three or more cirques are present on the same mountain peak, they are called a horn. The Matterhorn in Switzerland is the most famous example of a horn.

 How do we recognize glacial deposits? When a glacier melts, it dumps everything inside on the floor. They are unsorted, but they do form features. One such feature is called a moraine. There are several kinds of moraines, depending on their location. Moraines are unsorted deposits from glacial melting. Ground moraines are unsorted deposits from the bottom of the glacier. If the deposits are from the front of the glacier, they are terminal/end moraines. If they are from the side of the glacier, they are lateral moraines. If they are from the middle of the glacier, they are a medial moraine. Sometimes the deposits from a moraine accumulate over time. When this happens, a drumlin forms. Drumlins are spoon shaped deposits at the front of a glacier. The gentle slope points in the direction of movement while the steep slope points in the direction of the glacier. As glaciers melt, water runs from them downhill. The water carries sediment elsewhere. The extent of the sediment being deposited is referred to as the outwash plain.

 

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Stream erosion is the most common form of erosion on Earth because most of Earth is covered by streams of some sort. Whenever precipitation runs off, stream erosion occurs. Therefore, large rivers are not needed for stream erosion to occur. Raindrops can move silt and clay a few centimeters. This is erosion. If large amounts of runoff occur, larger sediments (like pebbles) can be moved. Sometimes channels called gullies are formed over time as more and more runoff occurs in the area. Sediment is abraded by water when rock particles rub against one another in transport. Sediment can be moved by water in one of three ways. Solution is when sediment is dissolved in water. Sediment traveling in this manner can be found anywhere in the body of water. Suspension is when sediment like clay and silt are moved at the top of the body of water. These particles float in water because they are too light to sink. Bed load is when giant particles are transported at the bottom of the river. These particles sink quickly and swirl around the river bottom as the river moves.

 The amount of water that a river can carry is called its carrying power. The larger the carrying power is will lead to more sediment capable of being moved because the river is stronger. Smaller carrying powers lead to less sediment being moved because of the weak nature of the river. Carrying power is related to a stream’s discharge, which is the volume of water that passes a point in a given amount of time. Flood stages have large discharges while calm rivers have small discharges. The greater the discharge means more erosion. As discharge increases so too does speed. Therefore, more sediment will be moved.

 All rivers are confined to a channel. When water is confined to a channel, a stream exists. Many times small streams flow into larger streams. The smaller streams are tributaries of the larger stream. The Mississippi River is a large stream with many tributaries. This is called a river system. When water occupies a channel for a large portion of the year, the stream is permanent. As sediment moves in streams, abrasion occurs. Abrasion forms rounded edges on the particles. What are some water erosion features?

 Over time streams carve deeper and deeper channels. The stream begins to carve V-shaped valleys because there is even erosion all around the channel. The stream continues to carve its channel until a flat slope is achieved. The gradient and speed of a stream helps us to determine the relative age of a stream. All streams start as gullies formed either by raindrops collecting in an area over time or from melting glaciers. Early streams carve a V-shaped valley because the slope is so steep, allowing the water to carve its way downhill. Over time the channel is carved deeper and deeper. The area that receives water from the stream is called a drainage basin or watershed. The divide is the point on the continent that separates eastward streams from westward streams and is the highest point on the continent. In the United States the divide is in the Rocky Mountains.

 As streams grow in size, they look for the path of least resistance. Easily erodable rock will be carved while more resistant rock will be ignored. Sometimes a more resistant rock is located in the middle of least resistant rock and forms a water gap. Because more resistant rock can be found near least resistant rock, the streams twist and turn. These shifts in direction are called meanders. As discharge increases over time, flooding occurs. The extent of the flood area is called the flood plain. This area is fertile and is the sight of much deposition.

 What are depositional features formed by streams? Depositional features are formed when the stream slows. Streams slow when the gradient is gentler, discharge decreases, and the shape straightens. When streams are straight, more friction is present and slows the stream down. The slowest portions of a straight stream are the sides and the bottom/top because friction is present in those areas. The fastest portion is just below the surface in the middle because of least friction. When the stream turns, it speeds up on the outside and slows on the inside. Therefore, deposition will occur on the inside of a stream at the turn. Therefore, the depositional features that are created are oxbow lakes, which are formed when meanders deposit so much sediment that they are cut off from the rest of the stream. Along flood plains deposition occurs.  If mounds of sediment are built up over time, natural levees are formed. Most streams enter oceans. When this occurs, streams slow down. As streams slow down, they deposit sediment at the mouth of the river. This sediment forms a delta (a triangular shaped mound of sediment).

 Look at the diagrams supplied in class to see the relationships among speed, shape, slope, and deposition.

 

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                                                          ROCKS AND MINERALS

 

A mineral is a naturally occurring inorganic solid with a definite atomic structure and composition. This means that minerals can not be created in a laboratory by humans. Minerals were never, are not, and never will be alive. No gas or liquid is a mineral. The atoms of he mineral inside are arranged in specific patterns; the most common pattern is a silicon tetrahedron (silica tetrahedra or plural), which is one silicon atom bonded to four oxygen atoms. Silicon and oxygen are the two most common elements in the crust of Earth. (See reference tables page 11) Composition refers to the elements inside the mineral. The reference tables page 16 show the only elements that you need to be familiar with.

 

 Minerals form deep within the Earth’s crust under intense heat and pressure. These two requirements are important because both are needed to fuse nearby elements together, forming the mineral.

 

 Not every location on earth has the same minerals nor do they have the same quantities of minerals. This leads to trade among nations, even to war among nations. Why? Minerals are important in our daily lives. We use minerals for 99.9% for everything we need daily.

 

 There are five mineral families. The first is the silicate family. These minerals are composed of silicon and oxygen, and, therefore, silica tetrahedra. These make up about 90% of all minerals. The second mineral family is the carbonate family, which is composed of carbon. These make up 7% of all minerals. The third family is the iron oxide family, which is composed of iron and oxygen. These make up 1% of all minerals. The fourth family is the iron sulfide family, which is made up of iron and sulfur. These make up 1% of all minerals. The last family is the sulfide family, which is made up of sulfur. These make up 1% of all minerals.

 

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We can identify minerals using several tests. There are eight tests we can use. They are color, density, luster, cleavage/fracture, streak, hardness, structure, and distinguishing characteristics.

 

 Color is least useful because many minerals have the same color on the outside. Therefore, we could determine the density of the mineral. However, many minerals have the same density and some dissolve in water if we were to compare its density to that of water. We could analyze its luster; it would either be metallic for metallic minerals or nonmetallic for nonmetallic minerals. These tests do not narrow down our task much. Therefore, we could analyze its cleavage or fracture. If it’s smooth, it has cleavage, but if it’s rough, it has fracture. But this still won’t narrow our search.

 When we perform the streak test, we analyze the powder or residue of the mineral. This is the true color of the mineral because oxidation corrupts the mineral. The hardness of the mineral is its ability to withstand being scratched by another mineral. The higher the number on Moh’s Scale of Hardness, the less it will be scratched. The Hardness Scale is:

10 – Diamond, 9 – Corundum, 8 – Topaz, 7 – Quartz, 6 – Orthoclase Feldspar, 5- Apatite, 4 – Fluorite,3 – Calcite,2 – Gypsum, and 1 – Talc.

 Hardness helps us to narrow down our choices, but the structure inside helps us to identify the family the minerals belong to. Distinguishing characteristics are special features that apply to a specific mineral and none other.

 

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Igneous rocks are formed by either magma or lava. Magma is molten rock underground while lava is molten rock above ground. There are two types of magma/lava. The first is felsic, which is light colored and low density. This contains aluminum. The second is mafic, which is dark colored and high density. This contains iron and magnesium. Extrusive rocks are formed by lava. These cool rapidly, forming either no crystals (noncrystalline glassy rocks) or small crystals (less than 1 mm fine rocks). Intrusive rocks form large crystals (1 – 10 mm coarse rocks) or very large crystals (more than 10 mm very oarse rocks). On the surface gas pockets may form when gases pop out of the rocks. These are vesicular rocks.

 

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Sedimentary rocks are formed by weathering and erosion. The sediments that are formed are deposited elsewhere. The sediments are held together by natural cements (quartz, calcite, feldspars) where they are buried, compacted and later cemented together.

 Sedimentary rocks contain particles and fragments from other rocks. Rocks of this nature are clastic. Their composition is mainly quartz, calcite, feldspars, clay, silt, sand, and possibly other substances. If these rocks contain fossils, they are bioclastic rocks. Fossils are only found in sedimentary rocks because magma melts fossils and pressure crushes them. If water evaporates and leaves minerals behind that form rocks, the rocks are crystalline rocks.

 You can recognize sedimentary rocks because they contain fossils, sediments, rounded sediments, sorted sediments, cracks, layers (called stratification), and interconnected mineral crystals.

 

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Metamorphic rocks are formed by heat and pressure deep within the Earth’s crust. This heat and pressure changes or metamorphoses existing rocks into new rocks. There are two types of metamorphism. Contact metamorphism is change on a small scale while regional metamorphism is change on a large scale. Contact metamorphism is what happens after an eruption when lava melts rocks into new ones. Regional metamorphism is what happens as mountains are raised up on the surface.

Foliated metamorphic rocks are those rocks with layers. You could clearly see these layers in the rock. Metamorphic rocks are denser than other rocks because so many minerals have been intertwined inside adding to its density. Foliation consists of mineral alignment – lining the minerals up inside the rock. Nonfoliated rocks are those without layers. These rocks tend to come from either underground or near volcanoes.

Metamorphic rocks have the following characteristics: a rock that looks like sedimentary rock but whose sediments are stretched or distorted, a grainy rock that can scratch glass because it contains quartz, a grainy rock that can not scratch glass because it contains calcite.

 The life cycle of a rock is identified in the rock cycle. This cycle has short cuts, which are the arrows inside the circle on your reference tables.

 

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                                                 PLATE TECTONICS

 

Earth’s lithosphere, which is the rock material covering Earth, is constantly in a state of flux. This is especially true for Earth’s crust – the very top layer of Earth. These changes are responsible for the buildup of mountains, the widening of the oceans, the formation of planes, earthquakes, volcanic eruptions, etc. Sometimes even rock layers may be altered in appearance because of these changes.

 According to theory, all rocks are formed horizontally or parallel to the ground. This principle is known as original horizontality. However, when Earth builds up pressure or when quakes/eruptions occur, these rocks may alter their appearances. You may have been on vacation and noticed bent rock layers, or bent strata. These bends are evidence of the changes discussed here.

 Some changes associated with the buildup of pressure are folds, tilts, and faults. Folded rocks are bent or curved. Tilted rocks are those that have been bent down only on one side. Faulted rocks are those that have cracks in them due to quakes or eruptions. Other changes include the uplifting of rocks from sea level to the tops of mountains. Evidence that supports this idea is the finding of marine fossils on mountain tops.

 

 One key change is caused by earthquakes. An earthquake is a violent shaking of Earth’s crust caused by the release of energy. Most earthquakes move along fault lines. Some fault lines can be found in your Earth Science Reference Tables on page 5. All earthquakes release waves of energy. Just like any other waves, these waves have crests, troughs, amplitudes, and wavelengths. Earthquake waves are called seismic waves. All earthquakes start at a focus. The focus is below ground where the quake truly begins. The waves then move outward from there. The location on the surface directly above the focus is called the epicenter. The epicenter is the sight of the most violent waves and the sight of the most destruction.

 Seismologists measure earthquakes using a seismograph. This is a drum with a needle on it. The drum sits atop a rock and shakes when waves travel through. The needle moves with the vibrations. At any given point in time there is an earthquake somewhere. Most are in the open ocean and most are tiny. We measure the magnitude of these waves with the Richter Scale, which is a measure of earthquake wave size on a scale from 1 to 10. Each number you travel up the scale equals a change in energy thirty-two fold. To give you an idea about the frequency of quakes and their energy, see below:

 

2.0 – over 1,000,000; same energy as a lightning bolt

3.0 – over 100,000; same energy as the Oklahoma City bombing   

4.0 – we feel these; about 12,000; a very large lightning bolt

5.0 - property damage; 2,000; an average tornado

6.0 – loss of life; 200; Hiroshima atomic bomb

7.0 – billions of dollars worth of damage; 20; a small volcanic eruption

8.0 – large loss of life; 3; Mount St. Helen’s eruption and the largest nuclear test ever conducted

9.0 – near total destruction; less than 1; impossible to duplicate

10.0- never happened.

 

 Hazards associated with earthquakes include tsunamis, property damage or loss, fatalities, other natural disasters, floods, etc. Always be prepared for an earthquake with a first aid kit, flashlights, batteries, transistor radios, etc.

 

 The different types of earthquake waves are P-waves (primary), S-waves (secondary), and L-waves (long). P-waves are the fastest waves and can travel through solids, liquids, and gases. These are back and forth motions. S-waves are the second fastest waves and move side to side. These waves only pass through solids. L-waves are the last to arrive and are the up and down motions. These are only on the surface.

 

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To find an earthquake epicenter, we need to utilize the time travel graph in our Earth Science Reference Tables. To read the graph, we need to remember that each line on the y-axis is equal to 20 seconds while each line on the x-axis is equal to 200 kilometers. We need to know the difference in arrival times between the p-waves and the s-waves. Once we know that difference, we can slide a piece of paper between then two lines on the graph until the top rests on the p-line and the bottom rests on the s-line. When we have what we want, we read the distance. To find the exact epicenter, though, we need three seismograph stations.

 

 We need to understand several things here. Not every station in the world receives waves. Those that do not receive waves are in a shadow zone. The p-wave shadow zone lies between 104 and 142 degrees from the epicenter of the quake on both sides. This is because they refract while in the outer core, which is inferred to be liquid. The s-wave shadow zone is 105 degrees away from the epicenter because they stop at a depth of 2900 kilometers, which is the outer core. This is the reason why the outer core is inferred to be liquid.

 

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We have already studied earthquakes and how they relate to plate tectonics. Now we will discuss volcanism and how it relates to plate tectonics. Volcanism is the study of volcanoes. We know that volcanoes spew lava onto the Earth’s surface and form extrusive igneous rocks. Volcanism, though, also encompasses features under the surface – so called plutonic features. More on this momentarily. We know the difference between felsic and mafic magma/lava. We can identify the areas of the world that have these types of magma. Shield cone volcanoes have mafic magma while cinder cone volcanoes have felsic magma. As eruptions occur, more lava is added to the volcano and it grows. An eruption is the giving off of gases, lava, and/or lava rock onto Earth’s surface or into the atmosphere through the neck or veins of a volcano. These could be gentle or violent.

 There are three types of eruptions. Rift eruptions occur at long, narrow fractures in the crust and are less violent. These eruptions occur mainly on the ocean floor and form shield cones. Subduction eruptions are eruptions along subduction zones. These are violent and form cinder cones. Therefore, we can say that rift eruptions release mafic magma onto the surface while subduction eruptions release felsic magma onto the surface. Hot spots are eruptions in the middle of a plate. These are similar to rift eruptions except that these produce cinder cones. We do not know what causes hot spots. Most eruptions occur along the Pacific Ocean in the area known as the Ring of Fire. Volcanic eruptions can alter weather patterns if they are violent enough. They pose a danger to nearby citizens. We can not predict the exact timing of an eruption although we can predict that an eruption can occur.

 Features underground are called plutonic features. Examples of these are:

1)      Dikes – sheets of igneous rocks that cut across other rock layers.

2)      Sills – sheets of igneous rocks that are parallel to other rock layers.

3)      Laccoliths – dome masses of magma that can not easily flow and are trapped in an area. These become magma chambers.

4)      Batholiths – cores of many mountains. The largest of all plutonic features. These are chambers of magma. A small batholith is a stock.

 

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Now that we know all about earthquakes and volcanoes, we can begin to speak about the layers of Earth. The first layer is the crust. The crust is thickest under the land surfaces and thinnest under the bodies of water. Most of the crust is basaltic rock. The air pressure is about 1 gravity. Temperature rises as you descend. It is only about 7-11 kilometers under the oceans but is about 30 kilometers thick under the landmasses.

 Beneath the crust is the mantle, which reaches a depth of 2900 kilometers. This is the thickest layer on Earth. S-waves stop at e depth of 2900 kilometers so we can infer that there is liquid beneath that depth. The mantle is divided into two parts – the asthenosphere which is liquid-like, and the rigid mantle which is rock. The crust and the asthenosphere are separated by the Moho, which is a thin layer containing the plates. From the crust to the Moho is called the lithosphere. The asthenosphere is inferred to be liquid-like because wave velocities decrease here. The asthenosphere reaches a depth of 700 kilometers. Pressure increases as you descend as does temperature. Actual temperature is above the melting point of rock, which explains the liquid state here.

 The rigid mantle is rock. The pressure here climbs as you descend as does temperature. Here, the actual temperature is below the melting point, which is why there is solid rock here. Wave velocities increase here. The depth reaches 2900 kilometers.

 The outer core does not display any s-waves, which is why it is inferred to be liquid. The actual temperature, therefore, must be higher than the actual temperature for this to happen. Temperature and pressure both increase as you descend. The outer core reaches a depth of 5100 kilometers.

 The inner core is inferred to be solid iron and nickel. Pressure and temperature rise as you descend. The actual temperature is below the melting point here. P-waves increase here, hinting at the solid nature of this layer.

 As we descend through Earth, density of the rocks increases.

 

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Since we have studied all the pieces we need to gain a full understanding of plate tectonics, we are in a position now to study the theory of plate tectonics. The theory of plate tectonics says that all of Earth’s crust is covered by a collection of moving plates. These plates move at a rate of 3 centimeters a year – the same speed that your fingernails grow in a year. The collection of plates is called tectonic plates, or lithospheric plates, or simply plates. These plates move on the asthenosphere, which is a liquid-like mass of magma. They float up and down due to convection currents caused by the plates expanding when near the magma and cooling when rising above the magma. They rise and sink a few millimeters a year. They follow currents as they travel across the globe. There are two types of plates – continental plates which carry continents and other landmasses, and are less dense, and oceanic plates which carry oceans, and are denser.

 There are three types of plate boundaries – convergent plate boundaries where two plates collide, divergent plate boundaries where two plates separate, and transform plate boundaries where two plates slide past each other. Convergent plates form mountains when two continental plates collide because they are the same density. They form trenches when a continental and an oceanic plate collide because the oceanic plate sinks beneath the continental plate. This is subduction. Divergent plates form ocean ridges when two plates separate. If two continental plates separate, a rift is formed on land. Transform plates slide past each other and build up potential energy that is released in the form of earthquakes.

 How do the plates move? Convection currents near the asthenosphere drive these plates. However, hot spots are locations in the middle of a continent or ocean not near plate boundaries.

 What do plate tectonics do? They alter the shape of the continents, for one. They create topography, or surface features like mountains. They widen the ocean floor and hint at the age of certain events like eruptions or changes in the direction of the axis or changes in the magnetic field of Earth. Other effects include environmental hazards, climate changes, changes in weather patterns, the rock cycle, major landmass features, and exposure of rock to weathering and erosion.  

 

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                                                                        GEOLOGIC HISTORY/LANDSCAPE DEVELOPMENT

 

Geologists use several methods to date rocks and geologic events (events that involve rocks). Two types of dating methods utilized are relative dating and absolute dating. Relative dating refers to the comparison of two rocks without knowing the exact age of the two rocks involved. For example, I am older than my students, or my students are younger than I am. All the freshmen are about the same age. These are all relative measures. Geologists use the principle of Superposition to relatively date rocks. This principle states that the oldest rocks are on the bottom of a series of rock layers while the youngest rocks are on top. This is relative dating.

 

 However, several problems exist with this method. One problem is that magma can cut the rock layers as it tries to reach the surface. Which is older – the rock layers or the igneous rocks formed by the magma?

 

 The rock layers had to exist before they were cut by magma. Therefore, the rock layers are older and the igneous rocks are younger. Magma cutting rocks inside Earth are called intrusions. At the same time, the volcano forming on the surface would be an extrusion because it is on the surface. All extrusions are younger than the rocks upon which they sit. If magma solidifies into igneous rock within a rock layer, it is called an inclusion. All inclusions are younger than the rocks in which they sit because the rock had to be there first. The same is true for all rock features – scratches, cracks, erosion, abrasions, etc. All features are younger than the rocks because the rocks had to form first.

 

 On the other hand, geologists use absolute dating when possible to obtain the exact age of the rock. For example, Pope Benedict was elected at the age of 78. Pope John Paul II died at the age of 84. All high school students at Cathedral Prep are in their teens. These are exact measures.

 

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Geologists are able to correlate or match rocks from one area of the world to rocks in another area of the world to gain a fuller understanding of past events and how they impacted the world. Several correlation techniques are utilized.

 

 First, geologists correlate by analyzing exposed bedrock. Exposed bedrock could be created by construction or by natural means. Exposed bedrock refers to bare rock in an area. Geologists walk the outcrop, or walk between the exposed bedrock and analyze the layers of rock they see for any similarities or differences. This is a good way to gain an understanding of previous plate movements.

 

 Second, geologists correlate by looking for similarities in the rocks. These similarities include – but are not limited to – mineral composition, appearance, color, and arrangement of rocks.

 

 Third, geologists correlate by utilizing index fossils. These are fossils that have existed for a specific point in time and over a large area. If two different areas of the world have the index fossil in the bedrock, then those two rocks are the same age.

 

 Fourth, geologists correlate by analyzing volcanic ash/meteorite deposits. These are collectively known as key beds. How is this done? Each eruption spews a specific mineral composition out of the Earth and in different quantities. If several areas have similar volcanic ash, then the rocks were formed from the same time. The same is true for meteorite deposits.

 

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Geologists use radioactive decay to date rocks absolutely. Radioactive decay refers to a rock emitting electromagnetic energy as it stabilizes. The length of time it takes for an element to stabilize is its half-life. Half of the radioactive substance disappears at a time. The rate of decay is unaffected by anything in nature. It will never change. Radioactive elements pass through several half-lives in their existence.

 

 A half-life is determined by halving the percentage of the radioactive element. For example, at any one time a radioactive element will be 50% radioactive and 50% stable after one half-life, 25% radioactive and 75% stable after two half-lives, 12.5% radioactive and 87.5% stable after three half-lives, etc.

 

 Geologists use Carbon-14 to date fossils because all life forms have Carbon-14 in them. After death, the Carbon-14 changes to Nitrogen-14. Its half-life is 5,700 years, so fossils older than about 10,000 years would contain very little Carbon-14- and be very hard to date.

 Uranium-238 is used to date igneous rocks which have this element. It takes Uranium-238 4.5 billion years to change into Lead-206. Recent rocks would not be dated with this method.

 Rubidium-87 is used to date any igneous rocks. It takes 49 billion years for Rubidium-87 to change into Strontium-87. Therefore, this method is useless for recent rocks.

 Potassium-40 is used to date any rock. It takes 1.3 billion years for Potassium-40 to change into Argon-40 and Calcium-40.

 

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To fully understand the evolution of New York State, we will study the reference tables referring to geologic history for New York State. We first see that time is divided into segments. The largest of these is an eon. There are two eons – the first was the longest (PRECAMBRIAN) and the second one is now (PHANEROZOIC). Each eon could be subdivided into eras. The Phanerozoic eon is comprised of the Paleozoic, the Mesozoic, and the Cenozoic eras. Each era is subdivided into periods, each period into epochs.

 

 For each one, we are given a length of time that each existed in millions of years. So, 1000 million equals 1 billion years ago while 0.1 million equals 100,000 years ago. For each epoch we are given a description of the dominant life that existed at that time. Furthermore, we see a black line that is interrupted at times. This black line represents rocks form that particular epoch that exists in New York State. If the line is there, we have rocks from then; if not, we don’t. The same is true for the fossils. The letters in the fossil column represents fossils at the top that have been found in New York State. These fossils are index fossils for this state. The lines for each fossil represent the time they dominated New York State. Periodically, different tectonic activities occurred in New York State. If there is a black line for the specific activity, that activity occurred. If not, it didn’t. For each epoch, geologic events are described that have shaped the landscape for New York State. Finally, there is a series of maps showing plate movements for North America. How did North America shift over time?

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