It’s not Jaws, but a 300-foot (90 meters) high and 330-foot (100 meters) wide triangular wedge of volcanic rock that’s been emerging from the crater of Mt. St. Helens since last Novembe, National Geographic magazines reports. It’s growing a rate of 4.6 feet (1.4 meters) a day.
“It’s an unstable column of rock. It will likely fall apart,” a geologist said. In the past week, blocks of rock have been falling from the tip of the fin at about the same rate as it is growing at the base. Scientists say these features typically last for weeks to several months. Nobody knows for sure when the current fin will collapse or be shoved aside.
The fin, which is steadily pushing other parts of the growing dome toward the west, has a smooth surface on the leading edge and is rough and crumbly on its sides.
“The reason for that highly smooth surface is because [magma] comes out at an angle, and the rock is literally getting ground against the walls of the vent,” another geologist said. “It’s like a rock in a rock-tumbler being ground, smoothed, and polished.”