Before the 1959 Hebgen Lake Earthquake, Sapphire Pool was a placid and majestic feature.
A jewel of Biscuit Basin, Sapphire Pool not only showed off a lovely hue, its edges were also ornamented with hundreds of geyserite knobs. Visitors remarked that these knobs looked like biscuits—hence, Biscuit Basin. Occasionally, it erupted, but it only attained heights of one to four feet.
The name “Sapphire Pool” was chosen by Frank J Haynes when he captioned a picture with the name, according to Lee H. Whittlesey in Yellowstone Place Names. G.L. Henderson used the name “Biscuit Terraces” to describe the geyserite knobs around it.
Today, Sapphire Pool is as it used to be: quiet and placid, with occasional bouts of turbulence. In fact, there is nothing to suggest that it would become a stupendously violent geyser, if for a brief period of time.
The hydrothermal system in Yellowstone National Park is intricate, created at haphazard underground through the serendipitous arrangement of fissures, crevices and air pockets. Any individual geyser is a complicated apparatus.
Now, imagine if something were to come along and entirely alter that intricate system? All hydrothermal systems are susceptible to change—aboveground and below. You can choke off a hot spring by dumping detritus—coins, rocks, handkerchiefs—into it, but seismic activity dramatically alters a thermal feature by changing up its inner plumbing. And it’s pretty impossible to predict what big seismic activity will do.
It would be like if a plumber came over and rerouted your entire house without telling you. Imagine turning on your kitchen faucet and finding out it actually turns on the upstairs shower now!
The 1959 Hebgen Lake Earthquake transformed Sapphire Pool into a stunning geyser, reaching heights of 150-200 feet. Furthermore, these eruptions, which happened every two hours and could last upwards of five minutes, pretty much obliterated the biscuits on the pool’s fringes. For the most part, these geyserite knobs were washed down the Firehole River. A marked change!
It didn’t last, of course. By 1964, the eruptions had subsided and by 1968 it was no longer a “true geyser.” It returned to its historically quiescent state. There was no returning the preponderance of biscuits, however.