Environmental Geology Lecture 2 Dr. Jwad K. Manii

Environmental geology lecture 2 Dr. jwad k. manii

FUNDAMENTAL COCEPTS

In this lecture we introduce concepts basic to the understanding and study of environmental geology. An understanding of the general thesis of each concept will be a significant help in comprehending and evaluating philosophical and technical material throughout the remainder of the text.

Concept One

The earth is essentially a closed system.

A system may be considered as any part of the universe that is isolated in thought or in fact for the purpose of studying or observing changes that take place under various imposed conditions (1). Thus, examples of systems might include a planet, a volcano, or an ocean basin. Most systems contain various component parts which mutually adjust, and each part exerts a partial control on the others. For example, the earth may be considered a system with four parts: the atmosphere: the hydrosphere; the biosphere; and thelithosphere.'The mutual interaction of these parts is responsible for the surface features of the earth today. Furthermore, any change in the magnitude or frequency of processes in one part will affect the other parts. For example, a change in the magnitude of the processes which produce mountains may affect the atmosphere by releasing volcanic gas and causing regional changes in precipitation patterns as a new rain shadow is produced. We know that the earth is not static. Rather, it is a dynamic, evolving system in which material and energy are constantly changing. Such dynamics might be considered evidence that the earth is an open system with no boundaries of energy or material. This interpretation is applicable as long as the continues to impart energy to the earth. However, considering natural earth cycles such as the water and rock cycles in which there is a continual recycling of earth materials, we can best think of the earth as a closed system or, in reality, a coalition of a large number of closed systems (2). For example, the rain that falls today will eventually return to the atmosphere, and the sediment deposited yesterday will eventually be transformed into solid rock. Therefore, although the earth is currently, and seemingly forever will be, an open system in terms of energy and material, it is essentially a closed system in terms of natural earth cycles.

Concept Two

The earth is the only suitable habitat we have, and its resources are limited.

The context of Concept Two includes two fundamental truths: first, that this earth is indeed the only place to live that is now accessible to us; and second, that our resources are limited, and while some resources are renewable, many are not. Therefore, we will eventually need large-scale recycling of many materials, and a large part of our solid and liquid waste-disposal problems could be alleviated if these wastes were recycled.

There are at least two dichotomous views on natural resources. One school holds that finding resources is not so much a problem as is finding ways to utilize them. In other words, the entire earth, including the ocean and atmosphere, has raw materials that can be made useful if we can develop the necessary ingenuity and skill .

Concept Three

Today's physical processes are modifying our landscape and have operated throughout much of geologic time. However, the magnitude and frequency of these processes are subject to natural and man-induced change.

The concept that an understanding of present processes which are forming and modifying our landscapes will facilitate the development of inferences concerning the geologic history of a landscape is known as the doctrine of uniformitarianism. Simply stated as the "present is the key to the past," uniformitarianism was first suggested by James Hutton in 1785, elegantly restated by John Playfair in 1802, and popularized by Charles Lyell in the early part of the nineteenth century. Today it is heralded as one of the fundamental concepts of the earth sciences.

Uniformitarianism does not demand or even suggest that the magnitude and frequency of natural processes remain constant with time. Furthermore, it is obvious that the principle cannot be extended back throughout all of geologic time because the processes operating in the oxygen-free environment during thefirst 2 billion years of earth history were quite different from today's processes. However, as long as the past continents, oceans, and atmosphere were similar to those of today, we can infer that the present processes also operated in the past. For example, if we have studied present alpine glaciers and the characteristic erosional and depositional landforms associated with alpine glaciation, then we can infer that valleys with similar landforms were at one time glaciated even if no glacial ice is present today.

Environmental geology lecture 2 Dr. jwad k. manii

Concept Four

There have always been earth processes that are hazardous to man. These natural hazards must be recognized and avoided where possible, and their threat to human life and property must be minimized.

Our discussion of uniformitarianism established that present processes have been operating a good deal longer than man has been on the earth. Therefore, man has always been obligated to contend with processes that tend to make his life difficult. Early in man's history, his struggle with natural earth processes was, probably a day-to-day. experience. However, his numbers were neither great nor concentrated, and, therefore, his losses from hazardous earth processes were not very significant. As man developed and learned to produce and maintain a constant food supply, his numbers increased and probably also the effects of hazardous earth processes. This resulted because population centers probably became local centers of pollution and disease. Furthermore, the concentration of population and resources increased the impact of periodic

earthquakes, floods, and other natural disasters. This trend has continued until today many people either are living in areas that are likely to be damaged by hazardous earth processes or are susceptible to adverse impact of such processes in adjacent areas.

Natural earth processes are called exogenetic if they operate at or near the surface of the earth and endogentic if they operate within or below the earths crust. Exogenetic processes include weathering; mass wasting; and either erosion or deposition by such agents as running water, wind, or ice. Volcanic activity arid diastrophism (processes which produce mountains, ocean basins, etc.) are common endogenetic processes. The work of organisms, including man, are primarily exogenetic processes; however, man is now able to cause some endogenetic processes such as earthquakes.

Environmental geology lecture 2 Dr. jwad k. manii

Concept Five

Land- and water-use planning must strive to obtain a balance between economic considerations and the less tangible variables such as aesthetics.

Scenery is now considered a natural resource, and the aesthetic evaluation of a site or landscape before modification is becoming an important part of the environmental impact statement. It is refreshing to note that consideration is now being given to the less tangible variables such as aesthetics, as well as the more traditional benefits-cost analysis. Until this revolution, the justification for a project was weighed by comparing the financial benefits over a period of time with the cost. The assumption now formulated is that there are varying scenic values, just as there are varying economic values, associated with a landscape and proposed modification.

The balancing of economic criteria with aesthetic criteria is ambitious and optimistic as well as very difficult. The problem is, On what basis can the two be compared.

Concept Six

The effects of land use tend to be cumulative, and, therefore, we have an obligation to those who follow.

This relationship between man and his environment probably existed until about 8,000 years ago when he developed his skill in the use of fire. The use of fire brought new effects different from earlier impacts on the environment. First, fire was capable ofaffecting large area of forest or grassland. Second, it was a repetitive process capable of damaging-the same area at rather frequent intervals. Third, it was a rather selective process in that certain species were locally exterminated while other species that exhibited a resistance to or rapid recovery from fire were favored . It is doubtful that early man's use of fire for protection and hunting had any long-term effect on the environment. However, as man became more and more dependent on an increasing variety of resources for his clothes, lodging, and hunting, he also increased his capacity to observe and test his environment. This early experimentation probably led to the use of plants and primitive agriculture about 7000 B.C.

Environmental geology lecture 2 Dr. jwad k. manii

Concept Seven

The fundamental component of every person's environment is the geologic factor, and understanding of this environment requires a broad-based comprehension and appreciation of the earth sciences and other related disciplines.

Concept Seven arises from the fact that all geology is environmental, and since we all live on the surface of the earth, we are both directly and indirectly affected by geologic processes . Therefore, an understanding of our complex environment requires considerable knowledge of such disciplines as geomorphology, the study of landforms and surface processes; petrology, the study of rocks and minerals; sedi-mentology, the study of environments of depositions of sediments; tectonics, the study of processes which produce continents, ocean basins, mountains, and other large structural features; hydrogeology. the study of surface and subsurface water; pedology, the study of soils; economic geology, the application of geology to locating and evaluating mineral materials; and engineering geology, the application of geologic information to engineering problems. Beyond this, the serious earth scientist should also be aware of the contributions to environmental research from areas such as physical, cultural, economic, and urban geography; biology; conservation; atmospheric science; chemistry; environmental law; architecture; and engineering. Environmental geology is the domain of the generalist with strong interdisciplinary interest.