Zion National Park warns visitors of deadly flash flood danger during monsoon season
Storms miles away can send a wall of water and debris through the park’s narrow canyons within minutes.
In midsummer, the Desert Southwest transforms into a landscape of thunderstorms and flash floods. But how exactly does that work? Let’s find out.
Conditions can quickly turn dangerous on clear summer mornings at Zion National Park in Utah, where officials are warning visitors that sudden monsoon storms can unleash deadly flash floods through the park’s famous slot canyons.
The National Park Service issued the warning after a severe thunderstorm sent visitors running for shelter in Zion Canyon on Wednesday. From July through September, moisture flowing into the Southwest can fuel rapidly developing afternoon thunderstorms and intense downpours.
The greatest danger may be hidden from view.
In this Saturday, Sept. 5, 2009 file photo, throngs of hikers trek through the Virgin River along The Narrows in Zion National Park, Utah. The Park Service already has recorded 5 million more visitors from this time last year at national parks creating traffic congestion, long waits, and crowded parks. (AP Photo/Ross D. Franklin, File)
Storms can form 15 to 20 miles upstream from Zion’s popular hiking areas, meaning visitors may never see the rain that sends water rushing through the park’s 288-square-mile watershed and into the Narrows. Floodwaters can arrive suddenly, carrying rocks, branches, tree trunks and other debris.
“Clear morning skies can quickly build into intense afternoon thunderstorms — transforming the landscape and creating serious hazards,” park officials said.
AccuWeather meteorologists say spotty thunderstorms will continue to pose a flash flood threat across parts of the Rockies, Great Basin and Southwest deserts as a powerful heat dome strengthens over the region. Storms that develop over the mountains can produce frequent lightning and flooding in nearby canyons, arroyos and valleys.
Why slot canyons can become deadly
Slot canyons have steep, narrow walls and few ways to escape. Rainwater flows quickly across the surrounding sandstone and funnels into the confined passages below, where water levels can rise within seconds or minutes.
A flash flood can surge through a canyon as a wall of water and debris 12 feet high or more, according to the National Park Service. Visitors cannot outrun a flood, and fatalities often result when rocks or other debris carried by the current strike people.
The danger is not limited to days when rain is falling directly over the park. Flash flooding can occur under sunny skies because a thunderstorm may be pouring rain elsewhere in the watershed.
Rock and debris slides on the Zion-Mount Carmel Highway. (Facebook/National Park Service)
Zion’s history shows how quickly conditions can become catastrophic, NPS history records show.
Seven canyoneers were killed after a flash flood swept through Keyhole Canyon on Sept. 14, 2015. Zion recorded 0.63 of an inch of rain, while the North Fork of the Virgin River surged from 55 cubic feet per second to 2,630 cubic feet per second in only 15 minutes.
In July 1998, two hikers were swept away and killed in the Narrows after the Virgin River’s flow increased nearly sevenfold, from about 109 cubic feet per second to more than 740 cubic feet per second. Rangers had warned visitors to avoid slot canyons after a flash flood warning was issued.
More recently, multiple hikers were knocked off their feet during a flash flood in the Narrows in August 2022. One visitor was carried several hundred yards and injured, while others became stranded on high ground. A 29-year-old hiker who disappeared during the flood was found dead three days later in the Virgin River.
Warning signs visitors should not ignore
File photo: A fast approaching monsoon rainstorm races in at Zion National Park near Springdale, Utah, on Monday, July 22, 2013. (Photo by Sandy Huffaker/Corbis via Getty Images)
Park officials urge visitors to check the latest weather forecast, park alerts and the daily flash flood potential before entering the Narrows or any other canyon.
Darkening skies, thunder, suddenly muddy water, floating debris, stronger currents or a growing roar from upstream can signal that a flood is approaching. Anyone who notices those signs should leave equipment behind and climb to higher ground immediately. Even gaining a few feet of elevation can save a life.
The park may close the Narrows and other slot canyons when conditions become dangerous. Officials emphasized that visitors should follow all closures, never cross flooded areas and always have an alternate plan when storms are possible.
“Conditions far away or upstream of your current location can change quickly and impact your trip,” the National Park Service warned.
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