Weather & Soil CHP 6 Earth

Soil Erosion Humans have increased the rate of soil erosion by removing vegetation through activities such as farming, logging, and construction.

How have human activities affected the rate of soil erosion? Hint 1. What Depends on Soil?

Mechanical Weathering NOT an example Oxidation

Of the following processes, which is not an example of mechanical weathering? Hint 1. Mechanical weathering involves the physical breakdown of rock into smaller pieces. NOTES: Oxidation is a process whereby rocks are altered by a chemical change (reaction with oxygen in water or air).

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

Considering the following list, which is not an example of chemical weathering? Hint 1. As opposed to mechanical weathering, chemical weathering involves the reaction of minerals chemically active fluids (such as water, or even air).

Feldspars Exposure of feldspar to water causes it to break down by hydrolysis into clay minerals and ions.

During hydrolysis, ions and clay minerals are produced by the decomposition of which of the following Earth materials? Hint 1. Hydrolysis involves the step-wise breakdown of mineral structures that were stable at high temperatures and pressures into other minerals that are more stable under conditions at Earth's surface. Minerals susceptible to hydrolysis will shed ions into natural (slightly acidic) waters, leaving behind chemically inert components to form new minerals.

Soil ~45 percent mineral matter - 5 percent organic matter - 25 percent - water & air

Soil in good condition for plant growth will be composed of ____. Hint 1. Soil forms where the geosphere, atmosphere, hydrosphere, and biosphere interact.

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Areas with high temperatures and abundant moisture will generally have the highest rates of chemical weathering.

Soil Unlike regolith, which consists only of weathered rock and mineral fragments, soil also contains organic matter, water, and air.

How does regolith differ from soil? Hint 1. Where Else Is Regolith? In addition to Earth, regolith is found on Earth's moon. However, the moon has no soil.

Soil erosion lower agricultural productivity and a lower quality of crops

Aside from the loss of topsoil, what are two detrimental effects of soil erosion? Hint 1. Why Soil Is Important Soil is extremely important because it allows humans to produce something that we need to survive as a species. What is it?

Water enters joints in the rock, where it preferentially weathers the corners and edges of the rock into a roughly spherical shape.

How can an angular mass of rock become a spherical boulder? Hint 1. The Name of the Process The name of this erosional process is spheroidal weathering.

Mechanical Weathering When water within fractures in a rock freezes, it expands, which applies pressure to the portions of rock immediately around it. This pressure breaks off pieces of the rock.

How can water cause mechanical weathering? Hint 1. The Forms of Water Keep in mind that water can commonly change between phases (i.e., gas, liquid, and solid).

Carbonic Acid -formed? Atmospheric carbon dioxide dissolves in raindrops.

How is carbonic acid formed in nature? Hint 1. The Chemical Composition of Carbonic Acid The chemical composition of carbonic acid is H2CO3.

Soil - Rainforest Rainforest soils are heavily leached.

Why do rainforest soils lack nutrients? Hint 1. Rainforest soils are reddish-orange in color and called oxisols. These soils develop in regions with high annual precipitation.

Physical Weathering Water expands when frozen and physically forces the rock apart.

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

Dissolution

Which type of chemical weathering is very efficient at weathering limestone? Hint 1. This type of weathering uses acidic fluids to break down calcite.

Sheeting

Which type of weathering produces an exfoliation dome? Hint 1. This type of mechanical weathering is created by the reduction of pressure, a process called unloading.

Soil classifications Soils are classified to facilitate comprehension, analyses, and explanations. This classification is especially useful for those who work in agriculture.

Why are soils classified, and for whom is it this classification useful? Hint 1. How Is Soil Classified? Soils are classified mainly by maturity, composition, moisture content, and climate.

Soil - rainforest Soluble materials such as calcium carbonate are severely leached from the soil.

Why are soils in tropical rain forests not well suited for farming? Hint 1. How Tropical Rain Forest Climates Affect Weathering Remember that a climate that has higher temperatures and humidity will have a higher rate of chemical weathering than a climate with low temperatures and humidity.

Soil The texture of soil strongly influences the soil's ability to transmit water and air.

Why is texture an important soil property? Hint 1. What is Soil Texture? Soil texture refers to the proportion of different particle sizes within the soil.

Mechanical vs Chemical Weathering Mechanical weathering results in broken pieces that are of the same composition as the original material, whereas chemical weathering alters the composition of the material.

How do the products of the two categories of weathering differ from each other? Hint 1. An Example from Each Category An example of mechanical weathering is a single sandstone breaking into smaller pieces of sandstone; an example of chemical weathering is an iron nodule turning into rust.

Chemical Weathering Areas with high temperatures and abundant moisture will generally have the highest rates of chemical weathering.

How does climate influence the weathering of rock? Hint 1. What Is Needed for Chemical Weathering For chemical weathering to occur, energy to fuel chemical reactions and a liquid medium for these reactions must both be present. The more energy and medium that is present, the higher the rate of chemical weathering will be.

The headstone on the left is made of granite, which is composed mostly of quartz and feldspar, whereas the headstone on the right is made of marble, which is composed of calcite.

In the pictures, why have the headstone on the right and the headstone on the left weathered differently? Hint 1. The Effect of Minerals on Weathering Rates Rocks that contain minerals that are more susceptible to dilute acids in water will weather at a noticeably quicker rate than rocks that contain more resistant minerals. NOTE: Dilute Acids

Mechanical Weathering allowing water to penetrate the rock at depth and begin the weathering process.

Joints in rock promote weathering by Hint 1. Where Weathering Typically Starts on a Rock Mechanical weathering will usually first occur on the surface of the rock, as it is this surface that first comes in contact with agents of weathering. How might a material that weathers rock reach deep within the rock?

Soil Climate

Of the five basic controls of soil formation, which factor is the most influential in soil formation? Hint 1. Two Things That Strongly Affect the Physical and Chemical State of Soils The amount of water available to the soil as well as how warm the region is greatly affect the erosion, formation, and composition of soil. topography climate plants and animals time parent material

Exfoliation Dome sheeting, where concentric slabs of rock break loose in reaction to the unloading of pressure.

Part complete An exfoliation dome forms as a result of Hint 1. The Rock Type That Forms an Exfoliation Dome Exfoliation domes form from large masses of igneous rock (often granite).

Quartz is extremely resistant to all forms of chemical weathering. Quartz is not affected by hydrolysis, oxidation, or dissolution because it is an extremely resistant mineral.

Sand dunes are typically dominated by quartz grains and very little other mineral matter. Why does this selection occur? Hint 1. What property of quartz allows it to persist even after other minerals have been weathered away? Think about the weathering processes that would be active in dune-forming regions. How would quartz be influenced by these processes, as compared to other minerals?

ALL OF THEM - All these processes aid in the development of nutrient-rich Hawaiian soils. Volcanic rocks contain minerals susceptible to hydrolysis. Volcanic rocks contain minerals rich in iron, so they are susceptible to oxidation. Minerals in the volcanic rocks produce clay minerals as weathering by-products. There is abundant rainfall.

The Hawaiian Islands contain active volcanoes and are known for nutrient-rich soils and lush vegetation. What is the most powerful explanation for this? Hint 1. Soil formation in the Hawaiian Islands is the result of extensive weathering of volcanic basalts. Which of the following explains not only why the weathering occurs, but why the resultant soil is particularly good for plant growth?

Soil C horizon Partially altered parent material

The ____-horizon is very similar to the parent material. Hint 1. Soil-forming processes operate from the surface downward; therefore, the horizons closer to the parent material are less weathered than those that are farther away.

Chemical Weathering Calcite Calcite is soluble in water and dissolves, especially if the water is slightly acidic.

The chemical weathering process known as dissolution is most effective in the breakdown of which of the following minerals? Hint 1. Dissolution/solution involves the breakdown of minerals that are soluble in water. Which of the following would react with natural waters (which often carry min

Chemical Weathering Pyroxenes Minerals such as pyroxene that contain iron are very susceptible to oxidation.

The chemical weathering process known as oxidation would be most effective in the breakdown of which of the following Earth materials? Hint 1. Oxidation involves the reaction of certain chemical components of minerals with oxygen, forming new oxide minerals— common rust would be an example of an oxide.

WARM - HOT WET Environments ='s Chemical Weather COLD DRY or WET Environment ='s Mechanical Weathering Focus on the weathering type that is facilitated by freeze and thaw cycles. Is this a type of chemical weathering or mechanical weathering?

The two types of weathering are mechanical weathering, which involves the physical breakdown of rocks without a change in chemical composition, and chemical weathering, which breaks down rock components and alters mineral constituents. In both weathering types, water plays a major role in rock breakdown, but moreso in chemical weathering. For instance, chemical weathering needs water to act as a solvent and to transport corrosive ions. Hence, in arid and arctic climates (where water is typically not available or frozen) chemical weathering processes are restricted. Chemical processes are also (mostly) accelerated by higher temperature, so the high humidity and high temperature of the tropics make it a the place where chemical weathering predominates. Both composition and rock characteristics can influence how fast or slow a rock will weather chemically. A silicate mineral's resistivity to weathering correlates to its order of formation in Bowen's reaction series. Silicate minerals that crystallize early (e.g., olivine) are least resistant to weathering, whereas silicate minerals that crystallize late (e.g., quartz) are most resistant. Additionally, a rock with cracks and/or holes is more susceptible to chemical weathering. Chemical weathering tends to be more predominant in warmer weather. This is because increased temperatures speed up chemical reactions, wet conditions with enough water to help produce acidic substances are present, and living organisms that produce rock breaking acids can thrive. Hence, cold and wet conditions favor mechanical weathering and hot and wet favors chemical weathering.

Soil texture diagram Sandy Loam

Using the soil texture diagram above, identify the soil that consists of 60 percent sand, 30 percent silt, and 10 percent clay. Hint 1. Double-Checking Your Answer If you are unsure of the answer that you obtained from the diagram, check to see that the percentages of clay, silt, and sand added together equal 100 percent.

Mechanical Weathering

Weathering and Rates of Weathering - Mechanical Weathering Mechanical weathering involves the physical break down of rocks without a change in mineral composition. Weathering rates are controlled by the type of rock being weathered, the degree of fracturing of the rock, and the climate of the area the rock is located in. There are different types of mechanical weathering. In all cases, the rocks break down as a result of expansion due to factors such as seasonal freezing of water or growth of salt crystals in rock fissures, removal of overlying layers by erosion (causing large sheets of rock to peel off as a result of the decrease in pressure), and biological activity, which includes the action of animals, humans, plants, and microbes. It is not uncommon for rocks to experience several of these weathering types simultaneously. In this activity you will explore and test your knowledge about the different types of mechanical weathering and the changes that occur in rocks exposed to surface conditions. Part A - Types of Mechanical Weathering There are four main types of mechanical weathering: frost wedging in which rocks are broken by water freezing within cracks, salt crystal growth in which rocks are broken by salt freezing within cracks, sheeting in which rocks dome upward and peel off, and biological activity in which living things such as tree roots break rocks apart. What wedging is Wedging occurs when substances or organisms fill and expand narrow fissures in rocks. This can be accomplished by ice, salts, or plant roots. Hint 2. How exfoliation occurs Just as layers of your skin can peel off, or exfoliate, so do the exterior layers of rocks. This usually occurs when a previously buried rock body is exposed through erosion of the overlying material. When the overlying material is gone, the pressure it exerted on rock beneath it is also gone. Without that pressure, the newly exposed layers expand and break into sheets at the surface. Hint 3. How limestone caves are formed The dissolving power of carbonic acid plays an important role in forming limestone caves/caverns.

mechanical and chemical

What are the two basic categories of weathering? Hint 1. What to Look For The two categories of weathering are broad terms within which more specific types of weathering are grouped. As such, they differ distinctly from each other.

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

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

Mechanical Weathering Tree roots cracking a sidewalk Potholes forming in the street

What is an everyday example of mechanical weathering? Hint 1. Mechanical weathering involves breaking an object into smaller pieces without changing its mineral composition.

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

What is salt weathering?

The limestone is dissolved and carried away by underground water.

What occurs when carbonic acid reacts with calcite-rich rocks such as limestone? Hint 1. How Does Carbonic Acid Reach Limestone? Carbonic acid reaches limestone as a dissolved compound in water, whether through precipitation or percolating groundwater.

Mechanically Weathered the surface area of the rock is increased, which allows a greater amount of chemical weathering to occur.

When a rock is mechanically weathered, Hint 1. A Hypothetical Example If you had a perfect cube of butter and you cut it into eight cubes of butter, how do the combined volume and combined surface area of all eight cubes compare with the volume and surface area of the cube before it was cut?

biological activity - weathering salt crystal growth within rock fractures

Which of the below is not weathering by biological activity? Hint 1. What Qualifies as Biological Activity? Biological activity is any activity that is either intentionally or unintentionally caused by a living organism.

Soil profile - bottom to the top C horizon, = bottom Partially altered parent material B horizon, - Accumulation of clay transported from above E horizon, - Zone of eluviation & leeching A horizon, - Mineral matter mixed with some humus O horizon = top - Loose & partly decayed organic matter

Which of the following correctly lists the main soil horizons (in a well-developed soil profile) from the bottom to the top? Hint 1. What Is Below the Lowest Layer? Below the lowest layer of a soil profile is the unweathered parent material, which is also known as bedrock.