Sinkhole urban areas due to water main breaks or sewer collapses when old pipes give way. They can also occur from the overpumping and extraction of groundwater and subsurface fluids. Sinkholes can also form when natural water-drainage patterns are changed and new water-diversion systems are developed. Some sinkholes form when the land surface is changed, such as when industrial and runoff-storage ponds are created; the substantial weight of the new material can trigger a collapse of the roof of an existing void or cavity in the subsurface, resulting in development of a sinkhole. Sinkholes tend to occur in karst landscapes. Karst
Divisions on a Ground Divisions on a Ground Divisions on a Ground: Essays on Canadian Culture is a collection of essays by Canadian literary critic Northrop Frye, edited by James Polk and published in 1982. The collection includes lectures, addresses and previously published articles by Frye. "Divisions on a Ground" presents Frye's theorizing about Canada with respect to three main themes: Canadian literary writing, university education in Canada and internationally, and a more general "social order" perspective. This collection diverges from Frye's better-known "" in its approach to Canada in that it does not present the "Canadian imagination" in isolation, but rather as one