Yellowstone letters reveal 1925 explosion story was misplaced by 1,000 feet

A century-old mystery at Yellowstone’s Biscuit Basin has turned out to be less about a missing geyser and more about a misplaced sign. In 1925, a hydrothermal explosion dramatically altered part of the basin, but because nobody witnessed the event, the details were later pieced together from observations and correspondence. One particularly confusing clue was a “Black Pearl” sign that ended up about 1,000 feet from the actual geyser it was meant to identify. According to the U.S. Geological Survey’s Yellowstone Volcano Observatory, two letters written in 1926 have now helped reconstruct how the mix-up happened and clarify the history of the area.An explosion that went unnoticedThe 1925 event was relatively small compared with some of Yellowstone’s much larger hydrothermal explosions, but it still changed the landscape around Biscuit Basin. According to the USGS, the explosion happened near the Firehole River and tore through the area’s fragile sinter crust.