Download APES Chapter 10

Geology: Processes, Hazards, and Soils
 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
 Silicon
 Aluminum
 Iron
 Calcium
 Sodium
 Potassium
46.6%
27.7
8.1
5.0
3.6
2.8
2.6
 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.
 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).
 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.
 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.
 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.
 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.
 The interaction of processes that change rock from one
type to another.
Earthquakes and Volcanic Eruptions
 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.
 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.
 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.
Formation and Types
 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.
 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.
 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.
 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.
 About 1/3 of the nation’s original prime topsoil has
been washed or blown into streams, lakes, and oceansmostly 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.
 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
 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.
 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 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.
 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.
 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
Organic Fertilizer
Inorganic Fertilizer
 Improves ability to retain
 Easily transported,
water
 Improves soil structure
 Contains a wide range of
nutrients
 Stimulates beneficial soil
bacteria
stored, and applied
 Can target specific soil
nutrient deficiency
 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.