GEOL 101 1nd Edition Lecture 22 Outline of Last Lecture I. GroundwaterII. CavesIII. KarstOutline of Current Lecture I. GeysersII. PorosityIII. PollutionCurrent LectureHot Springs-Water is 11-16oF warmer than the average annual air temperature of the locality-The water for most hot springs is heated by cooling of igneous rock below-95% of the hot springs in the US are in the western half of the country, where volcanoes and igneous processes were most “recently” activeGeysers-Intermittent hot springs where water erupts with great force, often rising 100 to 200 feet high-Occur where extensive underground chambers collect water which is heated by hot igneous rock below-Groundwater heats, expands, and changes to steam and erupts-Temperature of water when it erupts at the surface: 212°F-Temperature of water at the bottom of the chamber:450°F- The water at the bottom is under pressure, so it remains liquid at higher temperatures-Tallest active geyser: Steamboat in Yellowstone- 300 ft (eruptions are sporadic)- Former champion was Waimangu Geyser in New Zealand, which reached heights of over1000 ft before a landslide altered the water table in 1904These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-Medium sized geysers can erupt thousands of gallons of water during one eruption- Water in hot springs and geysers has lots of dissolved minerals from the bedrock below-When these minerals come out of solution, they can form rock deposits- If the bedrock is made of silicate rocks, then a rock called geyserite will form- If the bedrock is made of carbonate rocks, travertine terrales may formYellowstone-Half of the world’s active geysers are in Yellowstone National Park (WY) including Old Faithful- Old Faithful erupts approximately every 90 minutes, reaching heights of up to 200 feet- Yellowstone is also home to many hot springs, most of which exhibit a unique array of microorganisms known as Thermophiles- Thermophiles are organisms that can survive (and thrive) in extreme heat environments-Groundwater moves exceedingly slow – typical rate of movement is a few centimeters per day-Energy for the movement is provided by force of gravity- Recall that groundwater moves from high points in the GWT to low points-The velocity of groundwater depends on the permeability and porosity of the rocksDarcy’s Law-Hydraulic gradient – water table slope-Hydraulic conductivity – how quickly or slowly fluid flows through specific substances- Takes into account the permeability of the substance, and the viscosity of a fluid-Discharge – volume of water flowing through an area*These three factors make up Darcy’s Law:Q=K A (h1−h2)dQ=dischargeK=hydraulic conductivityA=cross sectional area(h1-h2)/d=gradientPorosity-Porosity – percentage of void, or pore space, in a rock body-Calculated by dividing the total volume of pore spaces by the total volume of the rock- Example: if a sandstone has a total volume of 100 cm3 and 20 cm3 is pore space, then:o 20 cm3/100cm3=20% porosity - The porosity determines how much groundwater can be stored in the pore spaces-Different rock types have different porosities:- Intergranular porosity- Fracture porosity- Bedding plane porosity- Solution porosity-Types- Intergranular – due to spaces between grainso Sandstones, claystones, conglomerates- Bedding plane – due to space between the bedding of rock layerso Sedimentary rocks- Fracture – due to spaces along joint sets and fractures within a rocko All rock types- Solution (vuggy) – due to cavaties within rocks that have dissolved from mild acidso Soluble rocks: Limestones, marble, rock salt, gypsumHuman Interation-Wells- To ensure a continuous supply of water, a well must penetrate below the water table- Pumping of wells can causeo Drawdown (lowering) of the water tableo Cone of depression into the water tableo You can produce a cone of depression in liquid soap or lotion bottles with a pumpo As you pump several times, the soap level around the center tube goes down in acone-shape-Artesian Well– a situation in which groundwater is under pressure and rises above the level of the aquifer- Not all artesian systems are wells, artesian springs also existPollution-Sewage – most common problem- Contaminated groundwater can be purified naturally through mechanical filtering through sands and gravel- Extremely permeable aquifers, such as coarse gravel, have such large openings that groundwater may travel long distances without being cleaned. This is also a problem in cavernous areas.- Contaminated water that does not get filtered may travel downstream to someone’s well-Other contaminants include: fertilizers and pesticides, industrial materials, chemicals, landfills, and mine