This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Hiking a picturesque valley or climbing a craggy gorge are among the most exhilarating experiences in nature. As a geologist, I have hiked and climbed some of the most intense terrain in the world, including in the Andes, Middle Eastern deserts, the Balkans and the Appalachians.
I am particularly drawn to canyons that provide beautiful windows into the rock record and the geologic history of a place. However, these narrow valleys can quickly become extremely dangerous when water pours in. At Grand Canyon National Park in Arizona, at least two hikers died and a third was missing after powerful monsoon storms sent a deluge into one of the narrowest parts of the canyon on Aug. 29, 2026.
Two of the survivors who were rescued described seeing the water quickly rise over the trail as they clung to a ledge, fearing they might never see their families again. So, how do you balance a love of outdoor activities with managing this risk and hiking safely in canyons? To understand the dynamics of a flash flood, it helps to start with the geomorphologic aspect—understanding landforms and how they change over time.
In canyons and arroyos—steep gullies common to the Southwest—flash flooding can occur even when heavy rainfall happens far away. A person can be hiking under clear skies in a canyon and not be aware that heavy rain falling upstream or even outside the canyon means a disaster is unfolding. The steep gradients and narrow passageways that define these landscapes channel water, sending vast amounts rushing downstream.
Under these conditions, water can rise quickly in the narrow space of a canyon. The Grand Canyon flood involved heavy downpours in the heart of monsoon season. The intensity of the rainfall matters in a canyon.
Even in arid regions, which generally get low amounts of rain annually, heavy rainfall within a short period can create devastating floods. In 2018, a flash flood in Israel's Tzafit Canyon—an environment similar to the part of the Grand Canyon where the 2026 flood occurred—claimed the lives of 10 recent high school graduates who were hiking in the canyon. I grew up in that region and had hiked there many times, and I remember thinking about the incomprehensible suddenness: One moment you are appreciating the breathtaking views of the desert, and within minutes you are fighting a torrent of water you never imagined in such an arid place.
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