A COMMON TOPOGRAPHIC FEATURE EFFECT BY POROSITY AND PERMEABILITY IS Karst Topography What is Karst topography? topography developed in areas underlain by carbonate rocks, including limestone and dolomite. Karst topography includes features like caves and sinkholes and forms when limestone is slowly dissolved away by slightly acidic groundwater. Groundwater mixes with carbon dioxide to form carbonic acid. Limestone is a rock that is easily dissolved by carbonic acid. As the acidic groundwater moves through pores in limestone, the rock dissolves, enlarging cracks until an underground opening called a cave is formed. Groundwater not only dissolves limestone to make caves, but it also can make deposits on the insides of caves. Water dripping from the cave walls contains calcium ions dissolved from the limestone. If the water evaporates while hanging from the ceiling, the calcium carbonate is left behind and builds up to form a stalactite. Water dripping from the cave walls contains calcium ions dissolved from the limestone. If the water evaporates while hanging from the ceiling, the calcium carbonate is left behind and builds up to form a stalactite. Where water drops fall to the floor, a stalagmite forms. Where water drops fall to the floor, a stalagmite forms. Cave Development CAVE ENTRANCE Disappearing Stream NATURAL CHIMNEYS NATURAL BRIDGE If underground rock is dissolved near the surface a sinkhole may form. A sinkhole is a depression on the surface of the ground that forms when the roof of a cave collapses, or when rock near the surface dissolves. A sinkhole is a depression on the surface of the ground that forms when the roof of a cave collapses, or when rock near the surface dissolves. These are common in areas that have lots of limestone and enough rain water to keep the groundwater system supplied with water. These are common in areas that have lots of limestone and enough rain water to keep the groundwater system supplied with water. Sinkhole SINKHOLE SINKHOLE Karst topography is common in the Valley and Ridge Province of Virginia, where limestone is abundant. KARST TOPOGRAPHY FEATURES Human Impact on Groundwater Groundwater accounts for 20% of all water used in the U.S. Unwise use of this valuable resource can damage or deplete groundwater reservoirs Some of the problems related to groundwater use include: overpumping-lowering the water table subsidence contamination Pollutants Contaminants introduced at the land surface may infiltrate to the water table and flow towards a point of discharge, either the well or the stream. A SOURCE OF GROUNDWATER CONTAMINATION: SEPTIC TANKS Contamination results in a decline in water quality. ANOTHER SOURCE OF POLLUTION: STORAGE TANKS YET ANOTHER SOURCE OF POLLUTION: LANDFILLS Groundwater Moves Usually Slowly