Geology for Environmental Science 1401

1. Geology for Environmental Science 1401 Includes material in Chapters 6 (Plate Tectonics, Volcanoes, Earthquakes), Chapter 7 (Shoreline Ecosystems), Chapter 10 (Fossil Fuels), Chapter 13 (Water issues, Weathering, Erosion, Deposition of Sediments), Chapter 14 (Soils), and Chapter 15 (Minerals) as well as some additional material. Geology affects: The distribution of ecosystems. The distribution of resources. Position of continents which affects ocean currents, distribution of heat, climate patterns, wind, movement of weather systems. Rocks & climate affect soil composition.

2. How Geology affects Weather, Climate, & Ecosystem Distribution. Uplift of Air Masses by Mountains – Orographic Effect.

3. The Theory of Plate Tectonics is probably the most important aspect of modern geology, referred to as a “Unifying Theory”. It explains the locations of most volcanoes, the causes of most earthquakes, the locations & shapes of continents, the distribution of fossils and mineral resources. Past Plate Tectonic events are recorded in the “rock record” of igneous, sedimentary, & metamorphic rocks.

4. Late 19th and early 20th century geolo-gists had noti-ced similarities between land fossils (plants, vertebrate fossils) in sou-thern South America, sou-thern Africa, southern India, and western Australia.

5. Other geologists had observed similar igneous and sedimentary rocks on different continents. Alfred Wegener (1915) suggested the name Pangea for the supercontinent that broke apart to form the present day continents. Because he could not explain the mechanism for movement, his ideas remained hypotheses without supporting data. Post WWII seafloor mapping used sonar & magnetometers. Seafloor ridges & trenches, coupled with seismic data from earthquakes, and other data helped “close the loop” and explain how it happened.

6. Basics of Plate Tectonics Theory Earth’s crust consists of irregular plates of different sizes. Plates “float” on the semi-molten astheno-sphere (outer mantle) – “Isostacy”. Plates move in relation to one another. Plates are driven by vertical convection currents (conveyor belt movement). Plate interactions – Divergent (splitting); Convergent (subduction); Transform (plates slide past one another).

8. Divergent Zone – rising man-tle plume causes plates to separate, spread. Mid-Atlantic Ridge Convergent Zone – denser oceanic crust sinks into mantle beneath other plate margin. Sinking plate melts to form magma. Rising magma = volcanoes Transform Zone – Plates slide past one another. Plate movement = earthquakes

9. Short-term effects of Plate Tectonics Earthquakes occur in all three plate interactions. Some earthquakes from old activity. Volcanism assoc. with Divergent and Convergent zones. Long-term effects of Plate Tectonics Splitting (Rifting) of continents, changes in ocean basin characteristics, movement of continents affects climate. Mountain building occurs due to continental collisions (Alps, Appalachians, Himalayas) or inland from convergent zones (Andes).

12. Types of volcanoes & where they occur. Basaltic eruptions (quiet eruptions, hot, fluid lavas that flow easily) – Divergent (rift) zones and Hot Spots (Iceland, Hawaii). High temperature, low viscosity lavas produce shield volcanoes & cinder cones. Andesitic Eruptions (explosive ash & pyro-clastic eruptions interspersed with occasional lava flows) – Convergent zones (Mt. St. Helens, Mt. Pinatubo, El Chichon). Quartz increases magma viscosity, causes magma to “freeze”. Gases increase pressure. Alternating eruptions build large, conical “Stratovolcanoes”.

14. Geology as it relates to shoreline and aquatic ecosystems (Chapter 7). Rocks exposed on land are constantly sub-jected to chemical weathering and physi-cal weathering, both of which contribute to the degradation of rock. Erosion is the down-gradient transport of degraded rock (sand, gravel, clay) by way of streams & rivers to eventual deposition in the ocean. Once deposited in the ocean, longshore currents & wave action separate & redis-tribute sediments by size.

15. Chemical weathering – water & natural acids break down minerals. Physical weathering – frost action, expansion & contraction physically degrade minerals.

17. Over time, continued deposition of sediments produces continental shelves. Mixed sediments washed & deposited in relation to sediment size.

18. Freshwater aquatic ecosystems largely controlled by water depth, water energy, clarity. Marine aquatic ecosystems largely controlled by water depth, water energy, clarity, salinity, currents, sunlight,... Shallow water ecosystems generally have greater species diversity. Shallow water = greater warmth, more sunlight = more plants, wind & water current mixing of nutrients. Continental shelves – 10% of ocean area, hold 90% of ocean species.

19. Most sedimentary rocks were deposited in shallow marine (continental shelf) or transitional environments (beaches, tidal flats) (see pp. 148-153).

20. Types of shoreline ecosystems are affected by coastal topography which are affected by whether coastline is emergent or submergent. NE U.S. coastline is sub-mergent (little or no coastal plain, moun-tains closer to ocean), rocky shore habitats (p. 150) are more common. SE U.S. coastline is emergent (broad coastal plain – old continental shelf is adjacent to coastline), sandy shore habitats are more common. Boulders for erosion control create artificial rocky shore habitats.

22. In tropical and sub-tropical settings, distant to large landmasses, limestones may form, largely due to algae removing Calcium Carbonate - calcite (CaCO3) from seawater for internal structures. When algae die, calcite “needles” sink to bottom, recrystallize as limestone. The conditions for limestone deposition are favorable for the growth of coral reefs (p. 151) and other biologically “built” structures (bioherms). Reefs are strictly defined as “wave resis-tant structures”, though structures below the wave base are broadly included.

23. Bioherms are important because certain organisms “like” structures. Certain plants, corals, bryozoa require structures for attachment. This is the rationale behind the creation of artificial reefs. http://www.mms.gov/ooc/press/1994/40018.txt "The result is the same as an oasis in the desert," said Texas Artificial Reef Coordinator Hal Osburn. "Artificial reefs increase viable habitat and improve biodiversity." Once attached organisms are present, other organisms are attracted.

25. Many of the important “reef building” corals have symbiotic or mutualistic relationships with certain types of algae. Algae provide oxygen & nutrients to polyps, while stony skeleton provide protection for algae. When corals are stressed, they “bleach” and expel the algae. If the corals do not re-establish a relationship with that species or another species of algae, the coral may die within a few weeks/months. Sources of stress: pollution, airborne microbes, damage from ships, divers, predation by fish, etc..

26. Corals have not always been the dominant reef builders. The Permian-aged (260 m.y. ago) Capitan Reef (TX – NM) was built by bryozoa, sponges, and algae. At the end of the Permian – coral extinction.

27. Chapter 10 - Fossil fuels – name derived from the derivation of coal and petroleum products from organic sources. Land plants – sources of coal and natural gas. Aquatic plants – sources of crude petroleum. Source rocks – dark colored, preservation of organic materials in anoxic, stagnant conditions. Organic liquids must be “cooked” likely for 1 million years+. Oil migrates to reservoir rocks (“traps”).

29. Factors affecting gasoline prices: World crude oil prices – Supply vs. Demand Concerns over terrorist threats to supplies Growth of China, India, US Taxes Regulations affecting gasoline blends Regulations affecting land access for drilling Weather issues affecting transport, off-loading of ships Conditions affecting refinery system

30. Chapter 13 – (pp. 281 – 283) (Fig. 13.4). Geological “roles” in the Hydrologic cycle: Convection heating of moist air for storms. Orographic Effect (Slide 2). Nature of soil & slope affect infiltration vs. runoff. Infiltration & percolation of rainfall to become groundwater. Eroded & deposited sediment may become aquifer material. Fractured rock may serve as an aquifer medium.

32. Pertinent terms relating to groundwater… Aquifer – body of sediment or rock that can store & transmit usable quantities of water. Recharge – replenishment of groundwater by Rainfall. Porosity - % of pore space in aquifer. Permeability – measurement of ability to transmit water. Unconfined aquifer – Directly recharged by percolating rainfall. Confined aquifer – Overlain & pressurized by “Aquiclude”/Confining Layer.

34. A “perched water table” exists where an aquitard locally inhibits downward flow of water, above the main water table.

41. Chapter 14 Soils Soils are most important to the First Trophic Level (Producers) of Terrestrial Eco-systems. The results of physical and chemical wea-thering provide for plants: A medium for root infiltration & plant support. Nutri-ents from degraded minerals. Pore space for water and oxygen. The quality of the soil affects the “Resiliency” of an ecosystem, i.e., its ability to bounce back from disturbances.

43. CLIMATE – Over time contributes more to soil character through the chemical and physical weathering of rock materials. Rate of weathering is dependent on available moisture and temperatures. Also important in nutrient cycling of humus. SLOPE – High slope gradient affects soil formation. As minerals break down, high gradient slopes are more susceptible to erosion. Nutrient cycling – natural breakdown of organics to form humus.

45. Bed Rock SaproliteOver time, with Physical and Chemical Weathering, the biotite gneiss (left) becomes the saprolite (right). When all traces of structure are lost, the saprolite becomes “residuum” (Ga. Red clay).

46. Process of Erosion Raindrops dislodge soil particles which are then moved by sheetwash. Surface irregularities concentrate some of flow into “threads of current” which form small channels or “rills”. Rills combine to form “gullies”. Rate of erosion is dependent on quantity of water, slope angle, eroded material, local base level, and other conditions. Gullies erode by down-cutting by water. May widen by sheetwash, rill erosion, and/or by mass-wasting.

49. Problems caused by excessive erosion: Loss of O and A layer of soil Loss of arable farm land when O and A layers are damaged “Silting-up” of streams, i.e., excessive mud hinders “filter feeders” (clams, etc.), gills of fish, etc.. Sand, silt clog stream channel. Growth of deltas into lakes diminishes the water capacity of the lakes, i.e., less water for drinking, recreation, irrigation, electric generation.

50.

51. Minerals are classified by their component anions , e.g. Halite (NaCl) and Sylvite (KCl) are both halides, Pyrite (Fe2S) is a sulfide, Quartz (SiO2) is an oxide. Most of the important “Rock Forming” minerals are silicates, e.g., quartz, feldspars, micas, pyroxenes, amphiboles, olivine. An ore is a rock that contains a mineral of economic interest and is called high grade when the mineral of interest is present in relatively large amounts and low grade if the mineral is present in small amounts. Market prices affect classifications.

52. Some ores are formed by igneous proces-ses, when molten rock solidifies (mag-matic concentration) (beryl, etc.) or when heated, pressurized water (hydrothermal processes) deposits dissolved minerals in suitable conditions (metals). Other economically important rocks and minerals (sand, gravel, kaolin, limestone) are derived from sedimentary rocks that were deposited on old continental shelves. Others (salt, gypsum) were deposited in old lakes, where water evaporation concentrated the dissolved minerals.

53. Still other mineral resources are present in metamorphic rocks, i.e., sedimentary or igneous rocks that have been altered by heat and pressure. Examples: Talc, marble, garnets, kyanite). The biggest environmental concerns arise from the extraction and processing needed to convert ore materials to usable industrial and consumer products. Old mine waste dumps in western U.S. present significant threats to ground water, surface water, air (distribution of particulates), eastern examples include Copper Basin, TN (Fig. 15.5, pp. 338-339).

55. Upsides/Downsides to mining methods: Subsurface Upsides: Less land disturbance, less waste generation, less groundwater disturbance. Downsides: More expensive, more dangerous, requires higher value ore. Surface Upsides: Less expensive, less dangerous, lesser valued ores are feasible. Downsides: More land disturbance, more waste generation, more water disturbance (ground & surface). Carthage, TN pollution issues