Sinkhole may exhibit a visible opening into a cave below. In the case of exceptionally large sinkholes, such as the Minyé sinkhole in Papua New Guinea or Cedar Sink at Mammoth Cave National Park in Kentucky, an underground stream or river may be visible across its bottom flowing from one side to the other. Sinkholes are common where the rock below the land surface is limestone or other carbonate rock, salt beds, or in other soluble rocks, such as gypsum, that can be dissolved naturally by circulating ground water. Sinkholes also occur in sandstone and quartzite terrains. As the rock dissolves,
Hornslet wind-turbine collapse which bent in the direction of the wind. The top half of the tower then sheared off at the bend and fell to the ground. The base of the tower remained standing. The debris of the turbine flew 200–500 metres away. No injuries were caused. The collapse was filmed from a nearby farmhouse. The film was shown on several TV stations and is available online. The turbine was out of service until June 2008 and was eventually replaced by a new wind turbine of the same design. Hornslet wind-turbine collapse The Hornslet Wind Turbine Collapse was a spectacular collapse of