Geology

There are some very large, ancient, ‘inactive’ sinkholes in some areas of the U.S. that are thousands of years old. Alabama claims to have the largest recent collapse sinkhole. It is called the “Golly Hole” and is located in Shelby County in the central part of the state. It collapsed suddenly in 1972. The sinkhole is about 325 feet long, 300 feet wide, and 120 feet deep. Learn more: USGS Water...

Sinkholes are just one of many forms of ground collapse, or subsidence. Land subsidence is a gradual settling or sudden sinking of the Earth’s surface owing to subsurface movement of earth materials. The principal causes of land subsidence are aquifer-system compaction, drainage of organic soils, underground mining, hydrocompaction, natural compaction, sinkholes, and thawing permafrost. Land...

There is no database of sinkhole collapses for the United States, so these data are unavailable. Some individual state geologic surveys track reported collapses within their state. Many sinkhole collapses are not reported to authorities or news organizations, and many occur in rural areas where they are unobserved. Learn more: USGS Water Science School - Sinkholes

Sinkhole damages over the last 15 years cost on average at least $300 million per year. Since there is no national tracking of sinkhole damage costs, this estimate is probably much lower than the actual cost. Learn more: USGS Water Science School - Sinkholes

A sinkhole is a depression in the ground that has no natural external surface drainage. Basically, this means that when it rains, all of the water stays inside the sinkhole and typically drains into the subsurface. Sinkholes are most common in what geologists call, “ karst terrain .” These are regions where the types of rock below the land surface can naturally be dissolved by groundwater...

Dinosaurs lived on all of the continents. At the beginning of the age of dinosaurs (during the Triassic Period, about 230 million years ago), the continents were arranged together as a single supercontinent called Pangea. During the 165 million years of dinosaur existence this supercontinent slowly broke apart. Its pieces then spread across the globe into a nearly modern arrangement by a process...

Paleontologists don't know for certain, but perhaps a large body size protected them from most predators, helped to regulate internal body temperature, or let them reach new sources of food (some probably browsed treetops, as giraffes do today). No modern animals except whales are even close in size to the largest dinosaurs; therefore, paleontologists think that the dinosaurs' world was much...

Dinosaurs went extinct about 65 million years ago (at the end of the Cretaceous Period), after living on Earth for about 165 million years. If all of Earth time from the very beginning of the dinosaurs to today were compressed into 365 days (one calendar year), the dinosaurs appeared January 1 and became extinct the third week of September. (Using this same time scale, the Earth would have formed...

From about 300-200 million years ago (late Paleozoic Era until the very late Triassic), the continent we now know as North America was contiguous with Africa, South America, and Europe. They all existed as a single continent called Pangea. Pangea first began to be torn apart when a three-pronged fissure grew between Africa, South America, and North America. Rifting began as magma welled up through...

Mount Rainier, Washington, at 14,410 feet (4,393 meters), the highest peak in the Cascade Range, is a dormant volcano whose glacier ice cover exceeds that of any other mountain in the conterminous United States. Mount Rainier has approximately 26 glaciers. It contains more than five times the glacier area of all the other Cascade volcanoes combined. Mount Baker (Washington) at 10,778 feet (3,285...

Yes and no. It depends on which glaciers you are considering. Parts of the Antarctic Continent have had continuous glacier cover for perhaps as long as 20 million years. Other areas, such as valley glaciers of the Antarctic Peninsula and glaciers of the Transantarctic Mountains may date from the early Pleistocene. For Greenland, ice cores and related data suggest that all of southern Greenland and...

Based on the most recent comprehensive survey in 2011, there were about 27,000 glaciers in Alaska. However, the number of glaciers is a misleading statistic. Scientists are more interested in total glacial land coverage as a measure. The number of glaciers is less important since large ones can split up into several as they retreat. The amount of area glaciers occupy in Alaska is trending downward...