ENVIR215 Spring 2005 1 Earth-Water Experiments: Getting Started The third series of experiments will deal with the earth and water in the earth. We will look at the flow of water in rivers and aquifers and the use of water for irrigation. We will explore experiments that simulate the fault motions that occur during earthquakes and look at two effects of earthquakes that are particularly threatening for humans: tsunamis and liquefaction. Finally, we will build a microcosm to simulate biological cycles on the earth. As in the first two sections section, you will do two experiments and spend about 3 lab periods on each. For each lab you will begin with the ‘Getting Started’ guide. Once you have successfully carried out these fairly explicit experiments, use the rest of the time available to make more explorations on your own. Part of the ‘exploration’ phase of the experiments involves writing notes in your lab-book on some of the other experiments, and where relevant, relating them to the experiments you have done. Both the ‘getting started’ phase and the ‘later exploration’ phase are important to carry out. List Of Air-Water Experiments EW1. Waves on the oceans and tsunamis EW2. River flow, sediment transport and erosion EW3. Ground water flow: Aquifers and pollution EW4. Irrigation: Evaporation and Salinization EW5. Brick and Spring Fault Model EW6. Compressional sand box EW7. Angle of Repose and liquefaction EW8. Microcosms and biospheresENVIR215 Spring 2005 2 EW1. Waves on the oceans and tsunamis Waves on water are normally generated by wind and flow, but they can also be generated by the sudden movement of the seafloor during earthquakes. This experiment involves finding the relation between frequency and wavelength, looking at the velocity of the fluid beneath the waves, seeing the difference between waves in shallow water and in deep water and watching the increase in amplitude of the motion when waves approach a shore. It will involve both a long, thin Plexiglas channel and the smaller tank we used for the atmospheric inversion experiment. Storm surges are great invasions of coastal lowlands by wind-driven waves; if they come at high tide they can be particularly bad, and they (not the wind) account for the majority of damage when hurricanes come to land. In the low-lying country of Bangladesh tropical cyclones can send ocean water over vast areas of the Ganges/Brahmaputra river delta, leading to major loss of life. Tsunamis are large waves created by earthquakes and as we are all too aware they can also lead to a major loss of life. Ocean waves also have analogs in many other systems, for example something like the refraction of light beams is seen as waves approach a beach. 1. Set up the long (8-foot) Plexiglas channel with about 5 cm. of water in it. Using a small piece of Plexiglas as a paddle, make waves (try to avoid making scratches, by taping up the end of the paddle). What do you see? What happens if you prop up one end of the tank? 2. Set up the smaller tank and make waves in deep water (at least 25 cm deep). How do they differ from waves in shallower water, say 5 cm. deep (you can compare simply by reducing the water depth here), and in very shallow water (less than 1 cm deep)? 3. Observe the motion of particles floating beneath the surface and on the surface. Describe the velocity pattern of water beneath a wave for both deep and shallow water. How do they differ? 4. Visit the flume and try making surface waves using a plate (aluminum or Plexiglas) as a wave maker). Create a ‘peninsula’ (part 5 in EW2) and look at waves that try to move upstream through the narrows where the flow is strong. This is a model of the waves you experience as a kayaker in Puget Sound or the San Juan Islands: big waves are found in unexpected places because of the pattern of the strong tidal flow. EW2. River Flow, Sediment Transport And Erosion On geological timescales sediment transport from the continents to the oceans is central to the cyclical process or mountain building and erosion that shapes our continents. Sediments can be transported across continents by wind, ice and rivers but rivers are globally the dominant mechanism. The high sediment loads carried by rivers produce rich soils on flood plains and repeated floods can replenish the soils in agricultural region. However, human actions can reduce the rate of sediment erosion, transport, and deposition by the construction of dams and by channelizing rivers to protect towns or farmlands. In this experiment you will work in the flume to understand the basics of sediment transportation and erosion. 1. Fill one straight of the flume with about half an inch of white sand. Use wet sand since the dry sand is in demand for other experiments. Add more sand as necessary. 2. Determine the minimum fluid velocity for sediment motion – the flow meter will not work (for long) in sediment-rich water so you will have to time ping-pong balls.ENVIR215 Spring 2005 3 3. Observe how individual grains move. Why do ripples (analogous to sand dunes on land) form? Try leveling out a section of sand and see what happens. 4. Study the patterns and rates of erosion around a pebble, a post, a curve (remove the baffles at one end of the flume), a spur or any object that interests you. 5. Put a ‘peninsula’ in the flume using one of the curved aluminum sheets from the ends. This makes a constriction of the flow, leading to strong effects on sediments (and also on gravity waves on the water surface). EW3. Groundwater Flow -Aquifers And Pollution Groundwater is a critical component fresh water supplies. In many regions groundwater is being withdrawn at unsustainable rates. In others, groundwater supplies have been damaged by pollution that can be very difficult to remediate. Cape Cod, Massachusetts is a sand-spit created by melting glaciers at the end of the last Ice Age (~ 12,000 years ago). Its inhabitants drink water from wells (and have septic systems), and yet sometimes experience salt water in their wells. In the US Midwest, great aquifers are a ‘mined’ for farming dry lands, using center-pivot irrigation (those circles you see from an airplane). The movement of water through these underground rivers is very slow. In this experiment you will study the basic mechanisms of groundwater flow through a porous medium and will look at simulations of flow