Rivers are flowing through the sky, and scientists are trying to understand more about them. Also called “atmospheric rivers,” this plume of moisture travels from the tropics carrying as much water as the Mississippi River has at its mouth, but although it can be a savior to formerly rain-starved places like California, they can be destructive forces of nature.

In this case, they’ve ended the horrendous drought in California. The atmospheric rivers have been flowing with a vengeance this winter, with 10 or more just in this season, according to reports. Scientists think that La Nina is largely to blame for the uptick in atmospheric rivers.

“Atmospheric rivers are relatively long, narrow regions in the atmosphere – like rivers in the sky – that transport most of the water vapor outside of the tropics,” NOAA says on its website. “These columns of vapor move with the weather, carrying an amount of water vapor roughly equivalent to the average flow of water at the mouth of the Mississippi River. When the atmospheric rivers make landfall, they often release this water vapor in the form of rain or snow.

“Although atmospheric rivers come in many shapes and sizes, those that contain the largest amounts of water vapor and the strongest winds can create extreme rainfall and floods, often by stalling over watersheds vulnerable to flooding,” NOAA adds. “These events can disrupt travel, induce mudslides and cause catastrophic damage to life and property. A well-known example is the “Pineapple Express,” a strong atmospheric river that is capable of bringing moisture from the tropics near Hawaii over to the U.S. West Coast.”