No one at Crater Lake National Park felt it, but the sleeping geological giant recently stirred in its long slumber.
For the first time since seismic equipment was installed at the park in 2011, three tiny earthquakes have been recorded, according to the Cascades Volcano Observatory, a U.S. Geological Survey facility based in Vancouver, Wash.
The quakes measured on Oct. 25 were miniscule, registering only a magnitude .08, the observatory reported.
"The bottom line is the Crater Lake area is not necessarily dead," said Seth Moran, a seismologist at the observatory.
"But we've waited 7,000 years since the last eruption," he added of the dormant volcano. "It could be quite a while before another one. But it is worth paying attention to on a human scale."
Crater Lake is in a caldera formed when Mount Mazama blew its top some 7,000 years ago.
Before last week's earthquakes, the most recent to have been recorded within the park were three quakes with magnitudes of 2.3, 2.6 and 2.4 occurring near Rim Village within 20 minutes of each other on the afternoon of Dec. 29, 1994, observatory scientists reported. The two largest of those were felt by people in the park, they noted. A 1997 USGS Crater Lake hazards report indicated they occurred along a system of regional faults.
"Those were literally the last earthquakes anyone knew about until now," Moran said. "Until the 25th, we hadn't seen anything like this."
However, because the Oct. 25 quakes were too small to be recorded outside the park by other instruments, their precise locations could not be determined. Based on how the quakes were recorded, the scientists believe they may have been centered near the northwestern corner of the crater rim at a depth of 5 to 10 kilometers.
The USGS' three seismic stations in the park each have highly sensitive GPS receivers.
"They are sending us data continuously," he said. "They can detect ground motion that is as little as a couple of millimeters."
Scientists are closely monitoring the data to keep tabs on any movement, he said.
"Whenever we put a new seismic network on a volcano, we always learn things we haven't learned before," he said.
— Paul Fattig
Read more in Wednesday's Mail Tribune.