An inviting-looking geyser in Yellowstone National Park belies the potential danger. Brocken Inaglory / Wikimedia Commons

A few months ago, the vacation for a young pair of tourists took a turn for the horrific when one of them fell into a boiling, acidic pool in Yellowstone National Park and "dissolved."

Colin and Sable Scott, a brother and sister from Oregon, left the authorized area and walked around the Norris Geyser Basin in Wyoming to find a thermal pool to take a dip in. While Colin was leaning down to check the temperature in one hole, he slipped and fell into it.

"In a very short order, there was a significant amount of dissolving," Lorant Veress, a Yellowstone deputy chief ranger, told the NBC affiliate KULR 8 last week after a report was issued about the incident. Colin Scott, 23, did not resurface and is believed to have died almost instantly.

Since 1870, at least 22 people have died from injuries related to thermal pools and geysers in the park. Below are a few reasons this can happen.

The pools are really, really hot

Yellowstone National Park sits atop a geologically active supervolcano. With magma bubbling so close to the surface, geysers and hot springs can reach burning temperatures.

The Scotts happened upon the hottest thermal region in the park, where temperatures can reach 237 degrees Celsius (roughly 456 degrees Fahrenheit). That's hotter than the temperature you cook most food at in an oven.

They're sometimes acidic

Most of the water in the park is alkaline, but the water in the Norris Geyser Basin is highly acidic. This is caused by chemical-emitting hydrothermal vents under the surface. Microorganisms also break off pieces of surrounding rocks, which adds sulfuric acid to the pools. This highly acidic water bubbles to the surface, where it can burn anyone who is exposed to it.

In 2012, a study published in the journal Geochemistry, Geophysics, Geosystems examined water that came from the Heart Lake Geyser Basin. They found that safe and unsafe water originated from the same underground spot but separated en route to the surface.

Some microorganisms can live there, but humans melt

Microorganisms called extremophiles have evolved to live in extreme conditions. These are what make the water look milky in color.

The conditions are deadly for humans, however, and the water can cause fatal burns and break down human flesh and bone.

"It is wild and it hasn't been overly altered by people to make things a whole lot safer — it's got dangers," Veress said. "And a place like Yellowstone, which is set aside because of the incredible geothermal resources that are here, all the more so."

In other words, stick to the trail.