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15.1: Introduction to Deposition - Geosciences

15.1: Introduction to Deposition - Geosciences


The topic of deposition is an important one, because, obviously, every sedimentary sequence was deposited somehow. This section is meant to serve as background for our consideration of the current-generated physical sedimentary structures in real sedimentary deposits.

Let me pose a question for you: Why does deposition happen? I wonder whether this strikes you as a trivial question or as a difficult question. In one sense, we can supply a simple answer: sediment is carried by a flow, and when the conditions are such that the flow becomes overloaded, the sediment is deposited. But in another sense, this is a superficial answer, because it does not account for the conditions under which a flow becomes overloaded, and we have to look for a more fundamental answer. (By overloading I mean that the flow, at a given time, is transporting a greater sediment load than what it would be transporting if the sediment transport were in equilibrium with the given flow.)

The most straightforward process involved in deposition is settling: the downward fall of sediment particles through the surrounding fluid by the pull of gravity (see Chapter 3). Keep in mind, however, that there is far more to deposition than just settling of sediment particles: you have to worry about where the sediment came from, how it got to the site of deposition, and why it was that more sediment was falling out of suspension than was being resuspended at the site of deposition. Considerations like this are absolutely critical to a really fundamental understanding of sediment deposition, but in my opinion not nearly enough attention has been given to such matters in the literature on sedimentation, either by hydraulic engineers or by sedimentary geologists. This chapter makes only the barest start on addressing such matters.


Acid Deposition

Sunlight increases the rate of most of the SO2 and NO reactions. The result is a mild solution of sulfuric acid and nitric acid. "Acid rain" is a broad term used to describe several ways that acids fall out of the atmosphere. A more precise term is acid deposition, which has two parts: wet and dry.

  • Wet deposition - refers to acidic rain, fog, and snow. As this acidic water flows over and through the ground, it affects a variety of plants and animals. The strength of the effects depend on many factors, including:
    • the acidity of the water
    • the chemistry and buffering capacity of the soils involved
    • the types of fish, trees, and other living things that rely on the water.
    • Dry deposition - refers to acidic gases and particles. About half of the acidity in the atmosphere falls back to earth through dry deposition.
      • Acidic particles and gases are blown by the wind onto buildings, cars, homes, and trees.
      • Dry deposited gases and particles can also be washed from trees and other surfaces by rainstorms. When that happens, the runoff water adds those acids to the acid rain, making the combination more acidic than the falling rain alone

      Process of Acid Deposition

      Prevailing winds blow the compounds that cause both wet and dry acid deposition across state and national borders, and sometimes over hundreds of miles. Please watch the 1:22 presentation below to learn more about the process of acid deposition.

      In this diagram, we are seeing how the acid deposition occurs. When the sources emit pollutants such as SO2, NOx, mercury, and volatile organic compounds, primarily SO2 and NOx, which are acidic gases, are deposited in two ways. One is dry deposition, the other one is wet deposition. The SO2 and NOx when they deposit back either gaseous pollutants or as particulates, it's called dry deposition. When these pollutants dissolve in water, cloud water, and then deposit, it's called wet precipitation. Or that is what we call acid rain. The dry, gaseous pollutants or particulate matter can sometimes get dissolved in water and come down again as wet precipitation. Receptors are the species that receive this acid rain and get affected. These receptors can be materials that we care about, or aquatic life, human beings, or lakes and streams.


      Mass-Wasting Triggers

      In the previous section, we talked about the shear force and the shear strength of materials on slopes, and about factors that can reduce the shear strength. Shear force is primarily related to slope angle, and this does not change quickly. But shear strength can change quickly for a variety of reasons, and events that lead to a rapid reduction in shear strength are considered to be triggers for mass wasting.

      An increase in water content is the most common mass-wasting trigger. This can result from rapid melting of snow or ice, heavy rain, or some type of event that changes the pattern of water flow on the surface. Rapid melting can be caused by a dramatic increase in temperature (e.g., in spring or early summer) or by a volcanic eruption. Heavy rains are typically related to storms. Changes in water flow patterns can be caused by earthquakes, previous slope failures that dam up streams, or human structures that interfere with runoff (e.g., buildings, roads, or parking lots). An example of this is the deadly 2005 debris flow in North Vancouver (Figure 15.6). The 2005 failure took place in an area that had failed previously, and a report written in 1980 recommended that the municipal authorities and residents take steps to address surface and slope drainage issues. Little was done to improve the situation.

      Figure 15.6 The debris flow in the Riverside Drive area of North Vancouver in January, 2005 happened during a rainy period, but was likely triggered by excess runoff related to the roads at the top of this slope and by landscape features, including a pool, in the area surrounding the house visible here. [The Province, used with permission]

      In some cases, a decrease in water content can lead to failure. This is most common with clean sand deposits (e.g., the upper layer in Figure 15.4 (left)), which lose strength when there is no more water around the grains.

      Freezing and thawing can also trigger some forms of mass wasting. More specifically, the thawing can release a block of rock that was attached to a slope by a film of ice.

      One other process that can weaken a body of rock or sediment is shaking. The most obvious source of shaking is an earthquake, but shaking from highway traffic, construction, or mining will also do the job. Several deadly mass-wasting events (including snow avalanches) were trigged by the M7.8 earthquake in Nepal in April 2015.


      Chapter 15 Mass Wasting

      After reading this chapter, completing the exercises within it, and answering the questions at the end, you should be able to:

      • Explain how slope stability is related to slope angle
      • Summarize some of the factors that influence the strength of materials on slopes, including type of rock, presence and orientation of planes of weakness such as bedding or fractures, type of unconsolidated material, and the effects of water
      • Explain what types of events can trigger mass wasting
      • Summarize the types of motion that can happen during mass wasting
      • Describe the main types of mass wasting — creep, slump, translational slide, rotational slide, fall, and debris flow or mudflow — in terms of the types of materials involved, the type of motion, and the likely rates of motion
      • Explain what steps we can take to delay mass wasting, and why we cannot prevent it permanently
      • Describe some of the measures that can be taken to mitigate the risks associated with mass wasting

      Figure 15.1 The site of the 1965 Hope Slide as seen in 2014. The initial failure is thought to have taken place along the foliation planes and sill within the area shown in the inset. [SE]

      Early in the morning on January 9, 1965, 47 million cubic metres of rock broke away from the steep upper slopes of Johnson Peak (16 km southeast of Hope) and roared 2,000 m down the mountain, gouging out the contents of a small lake at the bottom, and continuing a few hundred metres up the other side (Figure 15.1). Four people, who had been stopped on the highway by a snow avalanche, were killed. Many more might have become victims, except that a Greyhound bus driver, en route to Vancouver, turned his bus around on seeing the avalanche. The rock failed along weakened foliation planes of the metamorphic rock on Johnson Peak, in an area that had been eroded into a steep slope by glacial ice. There is no evidence that it was triggered by any specific event, and there was no warning that it was about to happen. Even if there had been warning, nothing could have been done to prevent it. There are hundreds of similar situations throughout British Columbia.

      What can we learn from the Hope Slide? In general, we cannot prevent most mass wasting, and significant effort is required if an event is to be predicted with any level of certainty. Understanding the geology is critical to understanding mass wasting. Although failures are inevitable in a region with steep slopes, larger ones happen less frequently than smaller ones, and the consequences vary depending on the downslope conditions, such as the presence of people, buildings, roads, or fish-bearing streams.

      An important reason for learning about mass wasting is to understand the nature of the materials that fail, and how and why they fail so that we can minimize risks from similar events in the future. For this reason, we need to be able to classify mass-wasting events, and we need to know the terms that geologists, engineers, and others use to communicate about them.

      Mass wasting, which is synonymous with “slope failure,” is the failure and downslope movement of rock or unconsolidated materials in response to gravity. The term “landslide” is almost synonymous with mass wasting, but not quite because some people reserve “landslide” for relatively rapid slope failures, while others do not. Because of that ambiguity, we will avoid the use of “landslide” in this textbook.


      Mass-Wasting Triggers

      In the previous section, we talked about the shear force and the shear strength of materials on slopes, and about factors that can reduce the shear strength. Shear force is primarily related to slope angle, and this does not change quickly. But shear strength can change quickly for a variety of reasons, and events that lead to a rapid reduction in shear strength are considered to be triggers for mass wasting.

      An increase in water content is the most common mass-wasting trigger. This can result from rapid melting of snow or ice, heavy rain, or some type of event that changes the pattern of water flow on the surface. Rapid melting can be caused by a dramatic increase in temperature (e.g., in spring or early summer) or by a volcanic eruption. Heavy rains are typically related to major storms. Changes in water flow patterns can be caused by earthquakes, previous slope failures that dam up streams, or human structures that interfere with runoff (e.g., buildings, roads, or parking lots). An example of this is the deadly 2005 debris flow in North Vancouver (Figure 15.1.6). The 2005 failure took place in an area that had failed previously, and a report written in 1980 recommended that the municipal authorities and residents take steps to address surface and slope drainage issues. Little was done to improve the situation.

      Figure 15.1.6 The debris flow in the Riverside Drive area of North Vancouver in January, 2005 happened during a rainy period, but was likely triggered by excess runoff related to the roads at the top of this slope and by landscape features, including a pool, in the area surrounding the house visible here.

      In some cases, a decrease in water content can lead to failure. This is most common with clean sand deposits (e.g., the upper layer in Figure 15.1.3 (left)), which lose strength when there is no water to hold the grains together.

      Freezing and thawing can also trigger some forms of mass wasting. More specifically, the thawing can release a block of rock that was attached to a slope by a film of ice.

      One other process that can weaken a body of rock or sediment is shaking. The most obvious source of shaking is an earthquake, but shaking from highway traffic, construction, or mining will also do the job. Several deadly mass-wasting events (including snow avalanches) were triggered by the M7.8 earthquake in Nepal in April 2015.

      Saturation with water and then seismic shaking led to the occurrence of thousands of slope failures in the Sapporo area of Hokkaido, Japan in September 2018, as shown on Figure 15.1.7. The area was drenched with rain from tropical storm Jebi on September 4th. On September 6th it was shaken by a M6.6 earthquake which triggered debris flows in the water-saturated volcanic materials on steep slopes. There were 41 deaths related to the slope failures.

      Figure 15.1.7 Slope failures in the Sapporo area of Japan following a typhoon (Sept. 4th, 2018) and earthquake (Sept. 6th, 2018) (Before and after Landsat 8 images: left: July 2017, right: September 2018).

      Media Attributions

      • Figure 15.1.1, 15.1.2, 15.1.3, 15.1.4, 15.1.5: © Steven Earle. CC BY.
      • Figure 15.1.6: © The Province. Used with permission.
      • Figure 15.1.7: “Landslides in Hokkaido” by Lauren Dauphin, NASA Earth Observatory. Public domain.

      the component of the gravitational force in the direction parallel to a slope

      the component of the gravitational force that acts directly into the slope

      the strength of a body of rock or sediment that counteracts the shear force

      A fine-grained sheet silicate mineral that can accept water molecules into interlayer spaces, resulting is swelling.

      a type of smectite clay that has strong swelling properties and is effective at absorbing dissolved ions

      an event, such as an earthquake or a heavy rainfall, that triggers the onset of a mass wasting event


      1 Chapter 1 Introduction to Geology

      After carefully reading this chapter, completing the exercises within it, and answering the questions at the end, you should be able to:

      • Explain what geology is, how it incorporates the other sciences, and how it is different from the other sciences
      • Discuss why we study Earth and what type of work geologists do
      • Define some of the properties of a mineral and explain the differences between minerals and rocks
      • Describe the nature of Earth’s interior and some of the processes that take place deep beneath our feet
      • Explain how those processes are related to plate tectonics and describe a few of the features that are characteristic of plate boundaries
      • Use the notation for geological time, gain an appreciation for the vastness of geological time, and describe how very slow geological processes can have enormous impacts over time

      Online Core Courses

      Register for the core classes that you need and learn about fascinating Earth sciences that impact your world every day. Classes are available online in the summer of 2020 through the College of Geosciences.

      The following core classes are available to all majors.

      ATMO 201: Weather and Climate (3 credit hours) covers structure, energy, and motions of the atmosphere climate fronts and cyclones atmospheric stability clouds and precipitation severe storms.

      Term:㺊-week term
      Core Curriculum Requirement: Life/Physical Science

      GEOG 201: Introduction to Human Geography (3 credit hours) surveys of the major systems of human-land relations of the world and their dissimilar developments the processes of innovation, diffusion, and adaptation stressed with regard to changing relationships between people and their environment.

      Term: Summer 1
      Core Curriculum Requirement: Social and Behavioral Science

      GEOG 203: Planet Earth (3 credit hours) covers Earth’s physical environment including climate, water, landforms, and ecosystems processes that control these systems and their global distributions human effects on these processes.

      Term: Summer 1
      Core Curriculum Requirement: Life/Physical Science

      GEOG 205: Environmental Change (3 credit hours) offers systems perspective on important attributes, elements, and connections within earth's physical environment dynamic nature of environment at multiple spatial and temporal scales.

      Term: Summer 2
      Core Curriculum Requirement: Life/Physical Science
      Other University Requirement: Cultural Discourse

      GEOG 213: Planet Earth Lab (1 credit hour) offers exercises and maps to illustrate principles of physical geography.

      Term: Summer 2
      Core Curriculum Requirement: Life/Physical Science

      GEOL 101: Principles of Geology (3 credit hours) surveys physical and chemical nature of the Earth and dynamic processes that shape it plate tectonics, Earth's interior, materials it is made of, age and evolution, earthquakes, volcanism, erosion and deposition introduces physical and chemical principles applied to the Earth. (NOTE: Not open to students who have taken GEOL 103 or GEOL 104.)

      Term: Summer 2
      Core Curriculum Requirement: Life/Physical Science

      GEOL 102: Principles of Geology Laboratory (1 credit hour) is an exercise-based introduction to the physical and chemical nature of the Earth and dynamic process that shape it rock and mineral types topographic and geologic maps complements GEOL 101 but may be taken independently.

      Term: Summer 1 and Summer 2
      Core Curriculum Requirement: Life/Physical Science

      GEOL 207: Dinosaur World (3 credit hours) surveys dinosaur paleobiology and paleoecology terrestrial paleoclimate and paleoenvironments of the Mesozoic dinosaur ancestors appearance and radiation of dinosaurs paleoecology and paleobiology of major dinosaur groups extinction of large dinosaurs and the Cretaceous/Paleogene mass extinction the appearance and ancestry of birds.

      Term: 10-Week term
      Core Curriculum Requirement: Life/Physical Science

      OCNG 251: Oceanography (3 credit hours) is an overview of the ocean environment interrelation of the subdisciplines of ocean sciences importance of the oceans to human beings human impact on the oceans.

      Term: 10-week term
      Core Curriculum Requirement: Life/Physical Science

      OCNG 252: Oceanography Laboratory (1 credit hour) offers virtual laboratory experiments and exercises demonstrating principles of ocean sciences emphasis on the unique interdisciplinary nature of the ocean and current ocean issues relevant to today's society.

      Term: Summer 1 and Summer 2
      Core Curriculum Requirement: Life/Physical Science

      Distance education differential tuition will not be charged for online courses in the summer of 2020 at an individual course level for all students in traditional degree programs. For students enrolled in distance education degree programs, there is no change in how they will be charged.


      Slope Strength

      The strength of the materials on slopes can vary widely. Solid rocks tend to be strong, but rock strength varies widely, so this is not always the case. If we consider just the strength of the rocks and ignore issues such as fracturing and layering, then most crystalline rocks (e.g., granite, basalt, or gneiss) are very strong, while some metamorphic rocks (e.g., schist) are only moderately strong. Sedimentary rocks have variable strength. Dolostone and some limestone are strong, most sandstone and conglomerate are moderately strong, and some sandstone and all mudstones are quite weak.

      Fractures, metamorphic foliation (excluding gneissosity and banding), or bedding can significantly reduce the strength of rock. In the context of mass wasting, this is most critical if the planes of weakness are parallel to the slope and least critical if they are perpendicular to the slope. This is illustrated in Figure 15.3. At locations A and B the bedding is nearly perpendicular to the slope and the layers of rock are relatively stable. At location D the bedding is nearly parallel to the slope and the layers of rock are relatively unstable. At location C the bedding is nearly horizontal, and the stability is intermediate between the two extremes.

      Figure 15.3 | Relative stability of slopes. The stability is as a function of the orientation of planes of weakness (in this case bedding planes) relative to the slope orientations. Source: Steven Earle (2015) CC BY 4.0. View source

      Internal variations in the composition and structure of rocks can significantly affect their strength. Schist, for example, may have layers that are rich in sheet silicates (micas) and these will tend to form weak layers. Some minerals tend to be more susceptible to weathering than others, and the weathered products are commonly quite weak (e.g., clay formed from feldspar). The side of Johnson Peak that failed in 1965 (Hope Slide) is made up of chlorite schist (metamorphosed sea-floor basalt) that has feldspar-bearing sills within it. The foliation and the sills are parallel to the steep slope. The schist is relatively weak to begin with, and the feldspar in the sills, which has been altered to clay, makes it even weaker.

      Unconsolidated sediments are generally weaker than sedimentary rocks because they are not cemented and, in most cases, have not been significantly compressed by overlying materials. Unconsolidated sediments can still bind together, and the strength of that binding is called cohesion. A cohesive sediment binds together strongly and if you picked it up with a shovel it would stick together in a lump (e.g., sand mixed with clay, clay). A sediment that is not very cohesive is weakly bound and would probably fall apart if you picked it up with a shovel (e.g., sand, silt). The deposits that make up the cliffs at Point Grey, Vancouver, B.C. include sand, silt, and clay, overlain by sand. The finer deposits at Point Grey are relatively cohesive (they maintain a steep slope, Figure 15.4 left). The overlying sand is not very cohesive (relatively weak) and has a shallower slope because there are many slope failures in the sand deposit.

      Figure 15.4 Left: Glacial outwash deposits at Point Grey, Vancouver, B.C. The dark lower layer is made up of sand, silt, and clay. The light upper layer is well-sorted sand, which has experienced slope failure and formed a cone of talus. Right: Glacial till on Quadra Island, B.C. The till is strong enough to have formed a near-vertical slope. Source: Steven Earle (2015) CC BY 4.0. View source

      In contrast to poorly cohesive sediment deposits, glacial till can be as strong as some sedimentary rock. Glacial till is typically a mixture of clay, silt, sand, gravel, and larger clasts and forms and is compressed beneath tens to thousands of metres of glacial ice (Figure 15.4, right).

      Apart from the type of material on a slope, the amount of water that the material contains is the most important factor controlling its strength. This is especially true for unconsolidated materials (e.g., Figure 15.4), but it also applies to bodies of rock. Granular sediments, like the sand at Point Grey, have lots of pore spaces between the grains. These spaces may be completely dry (filled only with air), moist (some spaces are water filled), or completely saturated (Figure 15.5).

      Unconsolidated sediments tend to be strongest when they are moist because the small amounts of water at grain boundaries holds the grains together due to surface tension. Surface tension is the tension at the surface of a fluid that allows the liquid to resist an external force. Liquids always tend to acquire the lowest surface area possible this happens because molecules at the surface of the fluid are attracted to the molecules below the surface). This is the property of liquid water that allows insects to walk over it. Dry sediments are held together only by the friction between grains, and if they are well sorted or well rounded, or both, this cohesion is weak, due to minimal grain contact. Saturated sediments tend to be the weakest of all because the water pushes the grains apart, decreasing friction between grains. Water will also reduce the strength of solid rock, if the rock has porosity, fractures, bedding planes, and/or clay-bearing zones, especially when the rock is saturated with water (saturated conditions).

      Figure 15.5 | Depiction of dry, moist, and saturated sand. Source: Steven Earle (2015) CC BY 4.0. View source

      Water pressure is an important factor in slope failure. As you move deeper in saturated sediment, the pressure of the water goes up due to gravity acting on the column of water above it this pressure is called hydrostatic pressure. The greater the depth below the surface of the water table (the point where the rock or sediments are saturated), the greater the water pressure acting on the materials. Holes are often drilled into rocks in road cuts to allow water to drain and relieve this water pressure. One of the hypotheses advanced to explain the 1965 Hope Slide is that cold conditions that winter caused small springs in the lower part of the slope to freeze, preventing water from flowing out. It is possible that water pressure gradually built up within the slope, weakening the rock mass to the extent that the shear strength was no longer greater than the shear force.

      Water also has an interesting effect on clay-bearing materials. All clay minerals will absorb a small quantity of water, which reduces the strength of the clay. The smectite clays (such as the bentonite used in cat litter) can absorb a lot of water, and this water pushes the clay sheets apart at a molecular level, which makes the clay swell. Smectite that has expanded in this way has almost no strength it is extremely slippery. Thus, slopes containing smectite clay are more likely to experience slope failure when they are saturated.

      Water can increase the mass of the material on a slope, because the mass of the water is a component of the overall mass of the slope material. This increases the gravitational force pulling the slope materials down. A water saturated body of sediment with 25% porosity weighs approximately 13% more than it does when it is completely dry, so the gravitational shear force is also 13% higher. In the situation shown in Figure 15.2b, a 13% increase in the shear force is enough to overcome the shear strength, and the block would move down the slope.

      Exercise 15.1 Sand and Water

      Source: Steven Earle (2015) CC BY 4.0.View source

      If you have ever been to the beach, you already know that sand behaves differently when it is dry than it does when it is wet. The following experiment will demonstrate the strength of sand when it is dry, moist and saturated.

      Find approximately half a cup of clean, dry sand (or get some wet sand and dry it out), and then pour it from your hand onto a piece of paper. You should be able to make a cone-shaped pile that has a slope of

      30°. If you pour more sand onto the pile, it will get bigger, but the slope should remain the same.

      Now add some water to the sand so that it is moist. One way to do this is to add enough water to saturate the sand, then let the water drain away for a minute. You should be able to form this moist sand into a steep pile (with slopes of

      Finally, put some sand into a cup and fill the cup with water so the sand is just covered. Swirl it around so that the sand remains in suspension, and then quickly tip it out onto a flat surface. It should spread out over a wide area, forming a pile with a slope of only a few degrees.


      Open Educational Resources

      This text is provided to you as an Open Educational Resource which you access online. It is designed to give you a comprehensive introduction to Geology at no or very nominal cost. It contains both written and graphic text material, intra-text links to other internal material which may aid in understanding topics and concepts, intra-text links to the appendices and glossary for tables and definitions of words, and extra-text links to videos and web material that clarifies and augments topics and concepts. Like any new or scientific subject, Geology has its own vocabulary for geological concepts. For you to converse effectively with this text and colleagues in this earth science course, you will use the language of geology, so comprehending these terms is important. Use the intra-text links to the Glossary and other related material freely to gain familiarity with this language.


      Ocean Interfaces & Human Impacts

      Metals

      The atmospheric deposition of certain metals to coastal and estuarine regions has been studied more than that for any other chemicals. These metals are generally present on particles in the atmosphere. Chesapeake Bay is among the most thoroughly studied regions in North America in this regard. Table 1 provides a comparison of the atmospheric and riverine deposition of a number of metals to Chesapeake Bay. The atmospheric numbers represent a combination of wet plus dry deposition directly onto the Bay surface. Note that the atmospheric input ranges from as low as 1% of the total input for manganese to as high as 82% for aluminum. With the exception of Al and Fe, which are largely derived from natural weathering processes (e.g., mineral matter or soil), most of the input of the other metals is from human-derived sources. For metals with anthropogenic sources the atmosphere is most important for lead (32%).

      Table 1 . Estimates of the riverine and atmospheric input of some metals to Chesapeake Bay

      MetalRiverine input (10 6 g year −1 )Atmospheric input (10 6 g year −1 )% Atmospheric input
      Aluminum16070081
      Iron60040040
      Manganese1300131
      Zinc501826
      Copper593.56
      Nickel10044
      Lead15732
      Chromium151.510
      Arsenic50.814
      Cadmium2.60.413

      Data reproduced with permission from Scudlark JR, Conko KM and Church TM (1994) Atmospheric wet desposition of trace elements to Chesapezke Bay: (CBAD) study year 1 results. Atmospheric Environment 28: 1487–1498.

      There have also been a number of investigations of the input of metals to the North Sea, Baltic Sea, and Mediterranean Sea. Some modeling studies of the North Sea considered not only the direct input pathway represented by the figures in Table 1 , but also considered Baltic Sea inflow, Atlantic Ocean inflow and outflow, and exchange of metals with the sediments, as well as the atmospheric contribution to all of these inputs. Figure 1 shows schematically some modeling results for lead, copper, and cadmium. Note that for copper, atmospheric input is relatively unimportant in this larger context, while atmospheric input is somewhat more important for cadmium, and it is quite important for lead, being approximately equal to the inflow from the Atlantic Ocean, although still less than that entering the North Sea from dumping. As regards lead, note that approximately 20% of the inflow from the Atlantic to the North Sea is also derived from the atmosphere. This type of approach gives perhaps the most accurate and in-depth analysis of the importance of atmospheric input relative to all other sources of a chemical in a water mass.

      Figure 1 . Input of copper, lead, cadmium, and lindane to the North Sea. Values in parentheses denote atmospheric contribution. For example, for copper the atmospheric contribution to rivers and direct discharges is 15 tons per year.

      (Figure reproduced with permission from Duce, 1998 . Data adapted with permission from van den Hout, 1994 .)


      Watch the video: 9 Introduction Lecture: Petroleum Geology Using Excel