National Park Service authorities have fined 13 French tourists for going beyond the safety boundary surrounding the active volcano Kilauea in Hawaii.

The visitors were on an unauthorized tour that promised to bring them close to the volcanic action.

While the 13 members of the tour were fined $100 and asked to leave the park, the tour guide faces fines up to $5,000 and even jail time, according to local station KHON2.

Kilauea is one of the most active volcanoes on Hawaii, and its bubbling lava attracts visitors from all over the world to see the volcano, standing 4,190 feet above sea level.

A photographer recently captured a stunning phenomenon of the volcano, in a video that appears to show blue lava streaming from Kilauea. The blue color is an optical illusion caused by the changing light at dusk, according to The Telegraph.

Another mesmerizing aesthetic phenomenon at Kilauea took place in December 2016, when bubbling lava formed “lava lakes,” or two deltas within the Pacific Ocean.