The constant seismic rumblings were spotted by the Pacific Northwest Seismic Network (PNSN), where seismometers on Mount Rainier recorded three straight days of nearly nonstop, high-energy seismic signals across the west flank of the volcano. Unlike the seismic activity tied to major earthquakes, the patterns being seen in Washington look more like a volcanic tremor, a type of nonstop hum or roar that begins when magma, hot water, and gas moves around inside a volcano.