Laboratory Manual for Introductory Geology 4e

EXERCISE 14.2
Name:
Course:
The Difference between Porosity and Permeability (continued)
Section:
Date:
(a) Are pumice and scoria porous? Permeable? Explain.
(b) Is a material that is similar to scoria more likely to function as an aquifer or an aquitard? Explain your answer.
(c) Is a material that is similar to pumice more likely to function as an aquifer or an aquitard? Explain your answer.
Groundwater’s slow pore-to-pore movement helps chemical erosion because the
longer water sits in contact with minerals, the more it can dissolve them. Similarly,
even a few drops of water placed on a sugar cube will eventually dissolve their way
through the cube. Unfortunately, chemical erosion can cause dangerous health
problems if humans or animals drink water in which poisonous material is dissolved.
For example, when groundwater wells were drilled in Bangladesh to provide drinking
water safer than that from streams contaminated with bacteria, the ground water
turned out to contain high concentrations of arsenic. An international effort is
under way to identify the source of the arsenic and devise methods for removing it
from the groundwater.
14.3 Landscapes Produced by Groundwater
Groundwater-eroded landscapes are called karst topography, after the area in
Slovenia and northeastern Italy where geologists first studied such landscapes in
detail, but spectacular examples are also found in Indiana, Kentucky, Florida, southern
China, Puerto Rico, and Jamaica.
Groundwater is the only agent of erosion that creates landforms from below the
surface of the Earth, and all karst topographic features are destructional (produced
by erosion). Caves and caverns, the largest groundwater erosional features, are
underground, unseen, and often unsuspected at the surface (FIG. 14.2a). In some
areas, extensive cave networks result from widespread chemical erosion. Sinkholes
366 CHAPTER 14 GROUNDWATER AS A LANDSCAPE FORMER AND RESOURCE