Chemical weathering

What do freeze-thaw and salt weathering have in common?

Both freeze-thaw and salt weathering require rain and force rocks apart physically.

Weathering

Rocks break down in many ways through a group of processes called weathering

What is the most important agent of chemical weathering?

water

Mechanical weathering would predominate.

-A cold dry environment experiencing uplift, in which material is being removed by erosion from an underlying pluton/intrusive igneous rock. -A cold wet environment at high elevation, in which freezing and thawing is common.

carbon dioxide

-A greenhouse gas -influences the rate of chemical weathering.

Which of the following external processes are clearly active/evident in the image above? Look at pic

-Erosion -Mass wasting

Slowest chemical weathering----Fastest chemical weathering

-Granite, with very few or no cracks -Granite, with abundant cracks -Basalt, with very few to no cracks -Basalt, with abundant vesicles(holes)

What is the definition of physical weathering?

-Mechanical processes break substances into smaller pieces. -All physical weathering does is break rocks and minerals apart. Nothing more is needed.

How can plants physically weather a rock?

-Plant roots exert outward pressures as they grow. -As plants grow, their roots thicken. If these roots are in a rock fracture, this can force the rocks apart.

Think about the soil horizons that make up the solum. Why isn't the C horizon part of the solum?

-The C horizon contains unweathered parent material. -The horizons that are part of the solum have broken down the original parent material. The C horizon has not.

Which of the following is an example of chemical weathering?

-a car fender getting rusty -The iron in the steel body of the car is bonding with oxygen to produce rust

Which of the following rocks would most likely experience sheeting?

-granite -Granite forms from magma cooling in subterranean magma chambers.

Which type of chemical weathering is very efficient at weathering limestone?

Dissolution

carbonic acid

Potassium feldspar weathers in the presence of water containing

Which climate contains the optimum environment for chemical weathering?

Warm and wet

What is an everyday example of mechanical weathering? CHOOSE ALL THAT APPLY.

-Tree roots cracking a sidewalk -Potholes forming in the street

dissolution reaction

-minerals dissolve in water making their chemical products ions within the water -example: halite usually forms where ocean water evaporates on the other hand it undergoes dissolution when placed in water -EX: -the salty taste of ocean water -caves formed in limestone

_________ is when various geologic materials exposed to the same environmental conditions will weather differently depending on their composition. --can occur because some materials are more resistant at the surface than others.

Differential weathering

What is salt weathering?

the formation of minerals in rock cracks during the evaporation of salty water, forcing rock apart

Mechanical

weathering is when physical forces break solid rock into smaller sediments.

Chemical

weathering is when there is a chemical transformation of rock into other compounds.

B horizon

− accumulation of clay particles from upper layers.

C horizon

− partially altered parent material that is easily identifiable.

The ____-horizon is very similar to the parent material.

C

Limits weathering

Rows of trees are planted on the border of a field to slow the wind and deflect it upward.

Fine-grained particles or iron oxide accounts for red, yellow, and brown colors in soil horizons. True or False?

True

Why does water frozen in the cracks of a rock help to break down the rock?

Water expands when frozen and physically forces the rock apart.

How does physical weathering cause chemical weathering to be more effective?

When a rock is physically broken into smaller pieces, there is more surface area on which chemical weathering can occur.

Salt crystal growth

can contribute to crumbling roadways in areas where salt is spread to melt ice and snow in winter.

Climate

has a crucial influence on the rates of all types of mechanical weathering.

Both tombstones in Figure 1 are from the same cemetery and were erected within four years of each other. Why is the younger marble tombstone more weathered than the older granite tombstone?

-The quartz and feldspars in the granite are more resistant to weathering than the calcite in the marble. -Not only are quartz and feldspars stronger than calcite, but calcite is more susceptible to acid dissolution.

How can the creation of ice result in physical weathering?

-Water expands in volume when freezing, exerting pressure on a container. -Water expands in volume when solidifying, which pushes outward on a container

How did weathering destroy New Hampshire's Old Man in the Mountain?

-Water migrated along fractures in the rock, where it froze and wedged the rock apart. -Ice wedging took advantage of pre-existing fractures in order to destroy the landmark.

chemical weathering

-Which breaks down rock components by altering mineral constituents and their internal structure -usually occurs in combination with mechanical weathering -water is critical for chemical weathering -alters the internal structure of rock materials.

Which of the following climates would have the greatest degree of ice wedging?

-cold in the winter, warm in the summer, and with moderate precipitation -Cold temperatures are necessary to create ice, but the water would flow into the fracture in the warm weather.

O horizon

-consists largely of organic material, still identifiable in uppermost layer.

Oxidation reaction

-iron-rich materials transform in the presence of oxygen in the air -is responsible for why an apple may turn brown after you cut it open and place it an open space -Iron weathers through the process -EX:-red color of rocks in Arches National Park -yellow-stained rocks that used to contain pyrite before it is weathered

When sheeting develops in an igneous pluton, fractures will develop in an orientation __________ to the direction of expansion.

-perpendicular -This effect makes layers separate from the pluton like layers of an onion.

Using the picture of the Entrada Sandstone in Figure 1, try to identify the evidence of physical and/or chemical weathering present.

-rusty color and fracturing -Physical and chemical weathering often works hand-in-hand to break apart rocks.

What changes are occurring in the igneous pluton that would result in sheeting?

-volume increase -With a reduction of confining pressure, the pluton expands.

Which of the following climates will have the highest rate of weathering?

-warm, wet climates -Water facilitates chemical reactions whereas warmer temperatures increase the energy to run them.

Which of the following components make up a healthy soil?

-water and air -mineral matter -organic matter -organic matter and mineral matter -A healthy, productive soil will have material in all three states of matter.

Which soil horizon will contain the greatest amount of organic material?

-O horizon -The O horizon is closest to the surface and will be the place where most organisms will live and die.

A vertical succession of soil horizons is called a soil profile.

True

E horizon

-light-colored, depleted of soluble materials, little organic material.

fastest weathering to slowest weathering (Land wise)

A. forest soil C. wetland soil B. desert soil

Which of the following is not an agent of erosion?

Heat

Which of the following locations will weather a block of marble the most quickly?

Honolulu, Hawaii -Hawaii is warm with plenty of water for chemical reactions

Which of the following components makes up the largest percentage of most soils?

Mineral portion

Which horizons make up the solum?

O, A, E, and B horizons

Sheeting ________ Frost wedging

The fissures formed as a result of _______ in exfoliation domes can be further enlarged by _____ in areas subjected to seasonal freeze-thaw cycles.

Mass wasting

involves the transfer of the disintegrated rock and soil downslope under the influence of gravity.

Which of the following features is the result of mass wasting?

Boulders

Biological activity

The break down of rock by moving fresh materials to the surface by burrowing animals is an example of mechanical weathering due to

Mechanical Wheathering

Which involves the physical break down of rocks without a change in chemical composition

What environmental condition is reduced on a batholith in order to generate weathering via sheeting?

Pressure

hydrolysis reaction

-Minerals are weathered in the presence of water -Takes place when acid rain reacts with rock-forming minerals such as feldspar to produce soluble minerals that are removed in solution -EX:-feldspar in granite rocks weathering to clay

fastest weathering to slowest weathering (mineral wise)

Peridotite, Gabbro, Dioritie, Granite

Where does the clay that accumulates in the B horizon come from?

-A and E horizons -The A and E horizons are above the B, so percolating groundwater will pick up the clay from those layers.

Chemical weathering would predominate.

-A hot environment with many short but intense rainstorms. -A hot humid climate with heavy precipitation that occurs all year. -A warm wet environment with above average yearly rainfall and several stormy seasons each year.

Which of the following scenarios best describes how sheeting will develop in an igneous rock?

-A subterranean pluton is exposed at the surface, releasing confining pressure. -As the pressure lowers, the rock will expand slightly, creating the fractures.

Which of the three images in Figure 2 would be most susceptible to chemical weathering and why?

-C: Physical weathering has created more surface area for chemical weathering to attack. -Chemical weathering does its work on the surface of the rock. The more surface there is, the more weathering that can take place.

Promotes weathering

-Humans remove trees and other vegetation in order to develop an area of land. -Animals burrow into the ground loosening the soil. -Lichens, which secrete acids, are present on the surface of a rock. -Consistent grazing by a herd of cattle.

________ weathering occurs when differences in resistance or environmental factors produce uneven surfaces on rocks.

Differential

Considering the following list, which is not an example of chemical weathering?

Exfoliation-is the breakdown of rocks by removal of overburden, a physical process.

________ is decayed remains of plant and animal life.

Humus

Which chemical weathering process is the primary method of weathering for feldspars?

Hydrolysis

Which horizons make up the topsoil?

O and A horizons

Erosion

is the physical removal of material by mobile agents such as water, wind, and ice.

Of the following processes, which is not an example of mechanical weathering?

oxidation-is a process whereby rocks are altered by a chemical change (reaction with oxygen in water or air).

Soil in good condition for plant growth will be composed of ____.

~45 percent mineral matter

A horizon

− composed of a mixture of humus and mineral material.