Huge walls of dust and debris, known as haboobs, can be both impressive and frightening for drivers in the U.S. Southwest when they suddenly appear.

These dust storms are triggered by thunderstorms and can form a dust wall that towers thousands of feet high and stretches miles wide, reaching velocities of 60 mph (97 kph) or more.

Here’s what to know:

How do haboobs form?

As Sean Benedict, a meteorologist with the National Weather Service in Phoenix, explains, thunderstorms can create powerful downdrafts that strike the ground at speeds between 50-80 mph (80-129 kph), spreading out in all directions.

The winds stir up loose dust and dirt, including from arid areas and farm fields, that get blown along in front of the approaching storm cell.

If thunderstorms cease to form, the dust gradually settles. However, air cooled by rain ahead of a storm can lift warmer air off the ground, sparking new storms and additional downdrafts, Benedict noted.

When that happens, the haboob can keep growing, and some travel as far as 100 miles (161 kilometers), Benedict said.

“It all relies on whether they’re moving through an area likely to produce dust,” explained Benedict, highlighting a well-known dust-prone path between Phoenix and Tucson.

Haboobs also can form in arid areas of Nevada, New Mexico and Texas.

It’s unclear whether haboobs will become more frequent

Experts indicate that since the 1970s, brief and localized rainfalls during the summer monsoon season have intensified in the U.S. Southwest as the atmosphere warms due to climate change driven by human activity.

At the same time, it’s raining less often as droughts last longer and some arid areas expand. Climate change increases the odds of both severe drought and heavier storms that could set the stage for more intense dust storms in the future.

Benedict said it’s difficult to say whether haboobs will become more frequent.

The storms require a specific set of circumstances, and land use, such as farming, can affect how much dust gets picked up, Benedict said.

Not all dust storms are haboobs, which are specifically associated with downdrafts from thunderstorms.

The National Oceanic and Atmospheric Administration says the Phoenix area experiences one to three large dust storms a year.

How to stay safe

The National Weather Service issues dust warnings if it anticipates that thunderstorms and high winds moving through dust-prone areas could reduce visibility to a quarter mile or less. That’s especially important when conditions are favorable for clusters of storms, Benedict said.

Haboobs can form quickly, catching drivers by surprise, blotting out the sun and reducing visibility to zero. Experts recommend that motorists pull off the roadways as far as possible, stop their vehicles and turn off their lights.

“People on the roads when they can’t see anything, they’re just gonna try to follow those taillights in front of them,” and run into parked cars, Benedict said. “If there is an accident, you might not know and you just get these big pile ups. So it’s definitely very dangerous when the visibility drops down that low.”

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