Comment: 02:47 - 04:14 (01:27)
Source: Annenberg/CPB Resources - Earth Revealed - 21. Groundwater
Keywords: groundwater, water, "fresh water", humans, "Earth's surface", lake, river, rainfall, bedrock, stream, fissure, basalt, granite
Our transcription: "Water, water everywhere; yet not a drop to drink."
So went the complaint of the Ancient Mariner as he looked out over the salty brine.
Although the Earth is sometimes referred to as the "Water Planet," only a tiny fraction is usable by human beings.
And most of this fresh water comes not from above but from beneath the Earth's surface.
This groundwater originates in various ways.
Water percolates continuously into the Earth from lakes and rivers, for example.
Most important of all, however, is rainfall.
In some places rainwater readily disappears into the ground.
Of course, water doesn't get beneath the land surface with equal ease everywhere on the globe.
When it lands on hard bedrock or asphalt pavement, it simply runs off to feed nearby streams and rivers.
But if there are cracks or fissures in the surface rock, the water can pass through to collect underground.
Even hard rocks, such as basalt or granite, usually have some fractures in them through which water can permeate.
Geology School Keywords