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APES Chapter 10. Geology: Processes, Hazards, and Soils. Geologic Processes:. Earth’s Structure:. Three concentric zones: Core —solid inner core of iron and liquid outer core (iron) which gives the Earth its magnetic poles.
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APES Chapter 10 Geology: Processes, Hazards, and Soils
Earth’s Structure: • Three concentric zones: • Core—solid inner core of iron and liquid outer core (iron) which gives the Earth its magnetic poles. • Mantle—thick solid zone consisting of iron, silicon, oxygen, and magnesium. The outermost layer of the mantle is a thin plastic layer of partially molten rock—the asthenosphere • Crust—outermost and thinnest zone of the Earth • Continental crust—29% • Oceanic crust—71%
Chemical makeup of the Crust: • Oxygen 46.6% • Silicon 27.7 • Aluminum 8.1 • Iron 5.0 • Calcium 3.6 • Sodium 2.8 • Potassium 2.6
Plate Tectonics: • Plates—major areas of the Earth’s crust whose boundaries are determined by lines of earthquakes and volcanoes • Lithosphere—crust and the rigid outermost part of the mantle above the asthenosphere • Plate Tectonics—the theory that explains the movement of the plates and the processes that occur at their boundaries (developed from the continental drift concept).
Plate movement produces mountains, volcanoes, the oceanic ridge system, trenches and other earth features. • Help explain how certain patterns of biological evolution occurred.
Three Types of Plate Boundaries: • 1. Divergent Plate Boundary—plates move apart in opposite directions.
2. Convergent Plate Boundary—plates are pushed together (subduction zone) forming a trench and causing earthquakes and volcanoes.
3. Transform Fault—plates move in opposite but parallel directions (slide past each other).
Geologic Processes on the Earth’s Surface • External Processes—those geologic changes based directly or indirectly on energy from the sun and on gravity (rather than heat from the Earth’s interior) • Whereas internal processes generally build up the earth’s surface, external processes tend to wear it down.
External Processes: Erosion and Weathering • Erosion—material is : • 1. dissolved, loosened, or worn away from one part of the earth’s surface and • 2. deposited in other places by water or wind.
Weathering—caused by mechanical or chemical processes that produce loosened material that can then be eroded. • Mechanical weathering—a large rock mass is broken into smaller fragments similar to the results you would get by using a hammer by the freezing and thawing of water, plant roots, etc. • Chemical weathering—one or more chemical reactions decompose a mass of rock.
Minerals and Rocks • The earth is composed of minerals and rocks. It is the source of almost all the nonrenewable resources we use: fossil fuels, metallic minerals, and nonmetallic minerals. • Mineral—an element or inorganic compound that occurs naturally and is solid. • Rock—any material that makes up a large, natural, continuous part of the earth’s crust.
Three Major Rock Types: • Igneous rock—formed below or on the earth’s surface from molten rock material. • Sedimentary rock—formed from sediment when preexisting rocks are (1)weathered and eroded (2)deposited in body of water, and (3)over time compressed into rock. • Metamorphic rock—preexisting rock is subjected to (1)high temperature, (2) high pressure, (3)chemicals, or a combination of these to change the structure of the rock.
Rock Cycle • The interaction of processes that change rock from one type to another.
Natural Hazards: Earthquakes and Volcanic Eruptions
Earthquakes: • Stress in the earth’s crust can cause solid rock to deform until it suddenly fractures and shifts along the fracture, producing a fault. The faulting or later abrupt movement causes an earthquake.
Earthquake Features: • Focus—the point of initial movement of the earth below ground. • Epicenter—the point on the surface directly above the focus.
Magnitude—the measurement of the severity of an earthquake. • Richter scale—a scale used to measure the magnitude of earthquakes. • Each unit on the Richter scale represents an amplitude that is 10 times greater than the next smaller unit.
Volcanoes: • An active volcano occurs where magma reaches the earth’s surface through a central vent or a long crack. • Volcanic activity can release: • 1. ejecta—debris ranging from large chunks of rock to ash that may be extremely hot. • 2. liquid lava • 3. gases such as water vapor, carbon dioxide, and sulfur dioxide.
Soil Resources: Formation and Types
Soil • A complex mixture of eroded rock, mineral nutrients, decaying organic matter, water, and living organisms. • Although soil is a renewable resource, it is produced very slowly by: • 1. weathering of rock • 2. deposit of sediments by erosion • 3. decomposition of organic matter
Mature soils are arranged in a series of zones called soil horizons. • A cross-sectional view of the horizons in a soil is called a soil profile.
Soil Texture—soils vary in their content of clay, silt, and sand. The relative amounts of the different sizes and types of mineral particles determine soil texture. • Soil with roughly equal mixtures of clay, sand, silt, and humus are called loams. • Loams are most often the desired soil texture for agriculture. • The soil triangle is used to determine soil texture.
Soil texture helps determine soil porosity—a measure of the volume of pores or spaces per volume of soil and of the average distances between those spaces. • A porous soil has many pores and can hold more water and air than a less porous soil. • The average size of the spaces or pores in a soil determines soil permeability—the rate at which water and air move through the soil.
Soil pH—the acidity or alkalinity of a soil measured on a pH scale, influences the uptake of soil nutrients by plants.
Soil Erosion • The movement of soil components, especially surface litter and topsoil from one place to another. • Moving water causes most erosion. • Soil scientists distinguish several types of water erosion.
Types of Water Erosion: • Splash Erosion—caused by the impact of rain drops. • Sheet Erosion—occurs when surface water moves down a slope or across a field in a wide flow and peels off fairly uniform sheets of soil.
Rill Erosion—occurs when flowing surface water cut small channels in the soil. • Gully Erosion—occurs when each successive rain cut the channels of rill erosion deeper until they become gullies or ditches.
The two major harmful effects of soil erosion are: • 1. loss of fertility and its ability to hold water • 2. runoff of sediment that pollutes water, kills fish and shellfish, and clogs irrigation ditches, boat channels, reservoirs, and lakes. • In tropical and temperate areas it takes 200-1000 years (depending on climate and soil type) for one inch of topsoil to form.
Global Soil Erosion: • The earth is losing 7-21% of its topsoil from actual or potential cropland each decade. • In developing countries, poverty and erosion interact in a destructive positive feedback cycle.
Soil Erosion in the U.S. • About 1/3 of the nation’s original prime topsoil has been washed or blown into streams, lakes, and oceans-mostly as the result of over cultivation, overgrazing , and deforestation. • Soil on cultivated land is eroding 16 times faster than it can form. The erosion rate is faster in heavily farmed areas like the Great Plains.
Desertification: • Process whereby productive potential on arid or semiarid land falls by 10% or more • Practices that leave topsoil vulnerable to desertification: • 1. overgrazing • 2. deforestation without reforestation • 3. surface mining without reclamation • 4. irrigation techniques that lead to increased erosion • 5. salt buildup and waterlogged soil • 6. farming on land that has unsuitable terrain or soil • 7. soil compaction by farm machinery and cattle hooves
Salinization: • Accumulation of salts in the soil. • Irrigation of land can help produce crop yields of 2-3 times greater than rain watering alone. However, irrigation water not absorbed into the soil evaporates, leaving behind a thin crust of dissolved salts in the topsoil. • Salinization can stunt plant growth, lower crop yields, and eventually kill plants and ruin land.
Soil Conservation: • Involves reducing soil erosion and restoring soil fertility. • Farming techniques to reduce erosion: • Terracing—converting steep slopes into a series of broad, nearly level terraces or steps that run perpendicular to the slope
Contour Farming—Plowing and planting crops in rows across the contour of gently sloped land. Each row acts as a small dam to help slow runoff. • Strip Cropping—planting alternating strips of a row crop (such as corn) and a grass crop (such as alfalfa)
Agroforestry (alley cropping)—several crops are planted together between trees and shrubs • Windbreaks (shelterbelts)—trees or shrubs planted to reduce wind erosion.
Gully Reclamation—restoring severely eroded bare land by planting fast-growing trees or shrubs to stabilize the soil, and building small dams and channels to divert water from the gully.
Fertilizers: • Fertilizers partially restore plant nutrients lost by erosion, crop harvesting, and leaching. • Fertilizers can be either organic—from pant and animal materials, or commercial inorganic—chemicals produced from various minerals.
Organic Fertilizers: • Animal manure—the dung and urine of cattle, horses, poultry, and other farm animals. • Green manure—fresh or growing green vegetation plowed into the soil. • Compost—produced when microorganisms break down organic matter such as leaves, food wastes, paper, and wood. • Spores of mushrooms, puffballs, and truffles—the rapidly growing mycorrhizae fungi help plants take in nutrients and be more disease resistant.
Inorganic Commercial Fertilizers: • Commercially made from various minerals. • Typically contain nitrogen, phosphorus, and potassium • Percentage of each nutrient represented by the numbers on the container, the first for nitrogen, 2nd for phosphorus, and 3rd for potassium
Advantages of Each: Organic Fertilizer Inorganic Fertilizer • Improves ability to retain water • Improves soil structure • Contains a wide range of nutrients • Stimulates beneficial soil bacteria • Easily transported, stored, and applied • Can target specific soil nutrient deficiency
Inorganic Fertilizer Disadvantages: • Does not add humus to the soil • Reduces soils ability to hold water • Lowers oxygen content • Typically supplies only 3 plant nutrients • Releases nitrous oxide, a greenhouse gas from the soil.
