The key to the crystals' formation is an upwelling of magma beneath the cave system. The heat caused the anhydrite in trapped pockets of groundwater to form selenite (a form of gypsum), which formed into crystals. Usually, something eventually disrupts this process. There are crystals all over the world, some of them quite large, but none quite as enormous as these. This particular cave remained in total isolation, with a steady temperature from the magma and a static environment in which the crystals were constantly bathed in water. This allowed them to grow for tens of thousands of years. Some crystals are more than 30 feet long and weigh more than 50 tons.

In the mid 1980s, the cave was drained (accidentally) by miners, but it wasn't discovered until 2000. Today, Cueva de los Cristales is protected by a steel door, put in place by the mining company that owns the cave. Visitors are limited, but the lack of water means the crystals could eventually collapse under their own weight, or lose their translucent beauty as gases infiltrate the cave. Image by: Carsten Peter, Speleoresearch & Films.

Cavern of Crystal Giants. [National Geographic]

Local geologists think drilling activities could've caused the hole, which was still growing as of Thursday, and threatening to consume a main highway nearby. Turns out, Daisetta is sitting on top of a giant salt dome, which is great for trapping oil. But drillers have a tendency to circulate salt water back down the holes the bore, which scientists think might've dissolved the dome and caused the collapse. Here is a photo of a shallower portion of the sinkhole, with barrels floating in it.

That's just a theory, though — how sinkholes form is a bit of a mystery of science. Some people think unusual groundwater percolation can carve out an underground cavern that suddenly collapses. Either that or the angry Earth could've sent giant Sarlacc worm-plants to eat all humans and digest us in excruciating pain over thousands of years.

Source: Associated Press

Non-Sarlacc images via AP.