A steep change in the slope of a riverbed can create rapids—regions where the water is especially fast and choppy—and dangerous. The same thing applies to rivers in the sky. Steep changes in altitude, temperature, or pressure can concentrate the water, creating rapids. They can cause downpours that are especially fast and heavy—and dangerous. That appears to be the case for recent springtime flooding in the Middle East.

Atmospheric rivers form when water evaporates from the ocean. As it rises, it’s caught in a jet stream, forming a tight, high-speed river. The average one delivers as much water per minute as the mouth of the Mississippi River.

When an atmospheric river crosses land, it can produce rain and snow. That can be helpful. But it also can be deadly, producing flooding, mudslides, and other dangers.

A recent study blamed deadly flooding in the Middle East in April 2023 on such a river, but one with rapids—waves with much higher concentrations of water. They dumped as much rain as some regions see in an entire year. Similar flooding in 2024 also might have been caused by rapids. The rapids were powered by evaporation from the Atlantic Ocean and the Arabian and Mediterranean seas.

Our warming climate is increasing the rate of evaporation. It’s also changing circulation patterns over the Atlantic. So the deserts of the Middle East could see more flooding in the years ahead—perhaps powered by rivers and rapids high in the sky.

The great white shark has the most fearsome reputation of all sharks. But it might not be the biggest of the predator sharks. That honor might go to the Pacific sleeper shark. The biggest one ever seen appeared to be about 23 feet long—longer than the biggest great white.

The Pacific sleeper is found mainly in cold waters around the rim of the northern Pacific Ocean. But some have been seen in warmer waters close to the equator.

The shark got its name because it was thought to spend most of its time near the bottom, waiting for prey to swim by—a “sleepy” sort of behavior. But at least one study found otherwise. The sharks were found to move up and down through the water column, from the bottom to near the surface. And some covered as much as three or four miles a day.

Pacific sleepers will eat just about anything. They prefer fish that dwell on the bottom, along with giant octopus. But their stomach contents also show other types of fish, snails, sea lions, and other prey. They might have hunted down some of them, and gobbled the already dead remains of others.

The shark hasn’t been studied that much. The largest one ever caught was about 14 feet long and weighed half a ton. But video cameras caught one that was estimated at 23 feet.

Pacific sleepers probably grow slowly and have a low reproduction rate. So they could be threatened by overfishing, mostly as bycatch—draining the population of what might be the largest of all predator sharks.

Currents at the bottom of the ocean can be just as fickle as wind currents at the surface. They can turn, speed up or slow down, and even reverse course. And they can change in just days or even hours.

That’s the conclusion of the most detailed study of sea-floor currents to date. Researchers anchored 34 instrument packages across a thousand-square-mile region off the coast of Mozambique, at the southeastern corner of Africa. The instruments monitored the currents for four years.

The study took place on the continental slope, at depths of up to a mile and a half. The slope is steep, and sharp canyons notch into it. Sediments tumble down the slope and through the canyons.

At the bottom of the slope, the currents generally flow from south to north. And in the canyons, they generally flow downhill. Speeds range from about a half to one-and-a-half miles per hour.

But researchers found a lot of variation. The speed changes, and so does the direction. Currents can even reverse direction—even in the canyons, where they sometimes flow uphill. Some of the changes are related to the tides or to passing storms or eddies. And others are related to the seasons, so they play out over days or weeks.

The researchers say a better understanding of sea-floor currents can tell them more about where ocean sediments come from. That can help them better understand changes in climate, the sources of pollution, and more—swirling along at the bottom of the sea.