UNITED STATES The damaged California dam is in the spotlight now, but it’s not alone among the facilities needing upgrades. (Nat Geo News) Why do we have dams? Use our resources to better understand. Teachers, scroll down for a quick list of key resources in our Teachers Toolkit, including today’s MapMaker Interactive map. Discussion Ideas Nat Geo News reports that there are more than 80,000 … Continue reading What’s Happening at the Oroville Dam?
Sinkhole [Physical Geography]
Noun. A sinkhole is a hole in the ground that forms when water dissolves surface rock. Often, this surface rock is limestone, which is easily eroded, or worn away, by the movement of water.
In a landscape where limestone sits underneath the soil, water from rainfall collects in cracks in the stone. These cracks are called joints. Slowly, as the limestone dissolves and is carried away, the joints widen until the ground above them becomes unstable and collapses. The collapse often happens very suddenly without warning. Water collects in these collapsed sections, forming sinkholes.
Sinkholes also form when the roofs of caves collapse. Sinkholes are often funnel-shaped, with the wide end open at the surface and the narrow end at the bottom of the pool. Sinkholes vary from shallow holes about 1 meter (3 feet) deep, to pits more than 50 meters (165 feet) deep. Water can drain through a sinkhole into an underground channel or a cave. When mud or debris plugs one of these underground caves, it fills with water to become a lake or a pond. (National Geographic Education)