Yellowstone National Park - rotten eggs, life and death

The bison are not the only thing in Yellowstone National Park that smells bad. This park has the dubious distinction of having the worst pong of anywhere I’ve visited so far in the USA … including Las Vegas (where a strong whiff of sewage wafted up from major construction sites on the strip).

Yellowstone is famous for its hot springs and geysers. Naturally, I expected a certain amount of stink from these high quality tourist attractions, but the experience considerably exceeded my expectations. I was not prepared to be feeling quite so light-headed by the time I’d finished my lap of the hot springs boardwalk.

The park lulls you into a false sense of security. The historic north entrance gate doesn’t emit any unpleasant odour, but travellers fairly quickly reach the in-park town of Mammoth Hot Springs. It starts here and continues throughout the park. Signs warn that “Toxic gases exist in Yellowstone.” Trust me, we noticed.

“Dangerous levels of hydrogen sulphide, carbon dioxide, and carbon monoxide have been measured in some hydrothermal areas. If you feel sick, leave the location immediately.” No advice is offered on how to tell the difference between feeling sick because you’re being poisoned by toxic gas and feeling sick because the stink alone is turning your stomach.

At Mammoth Hot Springs, many helpful signs remind visitors not to stray from the wooden boardwalk because this “Thin crust area” is apparently “dynamic” and several people have been “scalded to death.” Doesn’t that sound like a nasty, nasty way to die? It’s possibly slightly less horrible than being scraped to death with a vegetable peeler, but not by much. Suitably terrified, I kept carefully to the centre of the boardwalk at all times, no matter how alluring the water looked.


It wasn’t easy. The hot springs are incredibly beautiful. The water almost glows with implausible colours. Some of the water is so blue that it makes that toilet cleaning stuff look natural. The spring steams gently and invitingly, despite the incredible heat of the day. I really wanted to touch it, regardless of the smell, and the looming possibility of a horrible death by scalding.


Some of the springs are hotter than others. This one boiled steadily and the steam tumbled in thick clouds right across the boardwalk. Intimidated by the possibility of a fatal steaming I considered turning back, but eventually managed to convince myself that if I walked briskly it should be no worse than a smelly sauna.

This plateau was a weird, crusty wetland of pools, creeks, short waterfalls and gleaming white travertine, the rock that forms the terraces of Mammoth Hot Springs. The colours in the water come from thermophiles, the heat-loving micro-organisms that thrive in the springs. Different colours indicate different temperatures, and are thus a guide to how quickly scalding would be fatal. Colourless and yellow thermophiles grow in the hottest water, like this.


Orange, brown and green thermophiles thrive in cooler waters.


As inhospitable as it smells, the water is clearly incredibly fertile and teems with life. Dense mats of bacteria form in some of the waterways. These simple organisms are reminders of the beginnings of life. A few cells, endlessly replicating themselves are such humble beginnings.


Because of the “dynamic” (and potentially deadly) active crust, these springs and the colonies they support can vanish quickly, or resume suddenly as small earthquakes redirect the flow of water and volcanic heat below the surface.


I remained suspicious of even the most benign seeming bodies of water. Yellowstone is the only National Park in which I never got my feet wet.