Presentation on theme: "Distribution of Earth’s Water: 3% fresh water 97% salt water (oceans) <1% ground water 2% Ice <1% surface water 3% of Earth’s water is responsible."— Presentation transcript:
Distribution of Earth’s Water: 3% fresh water 97% salt water (oceans) <1% ground water 2% Ice <1% surface water 3% of Earth’s water is responsible for shaping (erosion) the majority of Earth’s surface.
Can rocks hold water? yes! Solid rock may look like it is solid, but, it actually has tiny holes or spaces between its cemented grains. This is called Pore space. In some rocks pore space may be visible or microscopic. How much water a rock holds depends on the amount of pore space. Porosity - The percentage of a material’s volume that is pore space. Porosity
(A)(B)(C)(D) A) All sand with no cement, has lots of pore space. B) Sand mixed with silt, has less pore space. C) Sandstone (solid rock), cement reduces pore space. D) Limestone, pore space between crystals, cracks and fissures. Porosity of a material is influenced by THREE factors: 1) Particle Shape Round particles have more space than angular or flat particles.
Porosity 2) Particle Sorting This is when particles are separated by size. A) A well-sorted material has particles the same size and this material will have the greatest pore space. (A) B) A material with a mixture of different sized particles (poorly sorted, for example gravel) will contain less pore space. (B)
Porosity 3) Particle Size Larger particles contain greater pore space than smaller size particles of the same shape. Question? Which type rock would have the greater amount of pore space, a sedimentary rock composed of sand particles or silt sized particles? Answer: A Sed. Rock composed of sand sized particles. Why???
Permeability Can rocks transmit Water? yes! If a rock has pore space, water can pass through. This is referred to as permeability. In some cases a rock may contain pore space but not be permeable. An example of a non-sedimentary rock that has pore space is Pumice. The amount of water and the movement of water beneath the surface of the ground is directly related to the porosity and permeability of the rock.
Permeability Permeability - the rate at which water or other liquids pass through the pore spaces of a rock. permeability increases with grain size because large- grained materials have large pore spaces and water passes through easily. sand and gravel are permeable materials. Impermeable - any materials that water or other liquids cannot pass through. clay (sediment) and shale (rock) are impermeable materials.
Sample Problem With reference to porosity and permeability, compare a rock which acts as an aquifer and one which acts as an aquiclude. Provide an example for each Answer: Aquifer has the ability to transmit ground water thus an aquifer must have high porosity and high permeability. Example: Sandstone Aquiclude tends to prevent ground water movement, thus an aquiclude must have low porosity and low permeability. Example: Shale