When a volcano in Iceland erupted for six months straight last year, more than 350,000 people went running—directly toward it. As Fagradals Mountain spewed lava, sightseers from around the world gathered to take selfies, roast marshmallows and hot dogs over the molten rock, and watch the red-hot spectacle unfold. This new global trend, called volcano tourism, has been fueled in part by social media. Tour companies worldwide have begun cashing in on the phenomenon by offering helicopter rides, hikes to lava lakes, and even volcano surfing, an extreme sport that involves sitting or standing on a metal board as you race down a volcano’s slopes. But experts warn that these adventures can be dangerous: Eruptions often produce poisonous gases that can cause lung damage, and sightseers can get hit by lava or rock, as was the case in 2018, when a “lava bomb” crashed through a tour boat in Hawaii, injuring 23 people. But despite the risks, visiting a volcano can be rewarding if travelers take precautions, experts say. As Frank Trusdell, a geologist in Hawaii, recently told reporters: “Every time you go somewhere that you see a geological process . . . it gives you a much greater respect for our planet.”