GEOL 101 1nd Edition Lecture 22 Outline of Last Lecture I Groundwater II Caves III Karst Outline of Current Lecture I Geysers II Porosity III Pollution Current Lecture Hot 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 active Geysers 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 over 1000 ft before a landslide altered the water table in 1904 These 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 form Yellowstone 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 rocks Darcy 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 K A h1 h2 Q d Q discharge K hydraulic conductivity A cross sectional area h1 h2 d gradient Porosity 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 Types Intergranular porosity Fracture porosity Bedding plane porosity Solution porosity Intergranular due to spaces between grains o Sandstones claystones conglomerates Bedding plane due to space between the bedding of rock layers o Sedimentary rocks Fracture due to spaces along joint sets and fractures within a rock o All rock types Solution vuggy due to cavaties within rocks that have dissolved from mild acids o Soluble rocks Limestones marble rock salt gypsum Human Interation Wells To ensure a continuous supply of water a well must penetrate below the water table Pumping of wells can cause o Drawdown lowering of the water table o Cone of depression into the water table o You can produce a cone of depression in liquid soap or lotion bottles with a pump o As you pump several times the soap level around the center tube goes down in a cone 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 exist Pollution 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 tailings