The teenage swimmers were spotted 2,300 feet offshore.
The cave stretches more than 200 miles.
"It's beyond comprehension."
For the second year in a row, weather trumps weapons when it comes to greatest risks.
The galaxy cluster, featured in a Hubble Space Telescope photo, weighs in at three million billion suns.
The new method offers a way to recycle one of the leading greenhouse gases responsible for climate change.
Texas has the most widespread contamination of radium in drinking water.
The refuge was opened up for oil and gas drilling in December.
Mudslides swamped southern California after heavy rains.
Understanding ice shelves is key to projecting sea level rise.
The bomb cyclone was just the tip of the crazy weather iceberg.
Chlorine levels specifically have been declining since at least 2005.
"There's just no time for these systems to recover."
The Hayward fault has been dubbed a "tectonic time bomb."
Let's break down the terms.
Winter Storm Grayson is churning up the East Coast.
Below-freezing temperatures persist across the U.S.
A recent study further unravels the mystery of Yellowstone's volcanic system.
Hundreds take the polar bear plunge for New Year's Day.
Two officers were injured at a New Year's Eve party in Tennessee.