The USGS has posted a Yellow code and an Advisory alert for six volcanoes they’re tracking across the country; USGS says these volcanoes are “exhibiting signs of elevated unrest above known background level.” The six with the heightened level of alert include the world’s largest active volcano, Mauna Loa, and Kilauea, Great Sitkin, Gareloi, Semisopochnoi, and Cleveland. While Mauna Loa and Kilauea are both on Hawaii’s Big Island, the rest under the Yellow code are in Alaska.
Within the United States, the USGS tracks 169 potentially active volcanoes, most of which are in Alaska. Alaska is home to many volcanoes, though; there are more than 130 volcanoes and volcanic fields which have been active within the geologically young last 2 million years. 50 have been active since the mid 1700s and AVO studies those too. Another place famous for its volcanoes is Hawaii; on the Big Island of Hawaii, Kilauea, Mauna Loa, and Hualalai are considered active and potential threats, however none are erupting as of today. Kilauea did start a fresh eruption in December 2020, but that eruption came to an end just weeks ago. The Hawaii volcanoes are monitored by the Hawaii Volcano Observatory (HVO) while the Alaska volcanoes are monitored by the Alaska Volcano Observatory (AVO.) In addition to the AVO and HVO, there are also the California Volcano Observatory , Cascades Volcano Observatory, and the Yellowstone Volcano Observatory. Each of those additional volcano observatories within the USGS are monitoring volcanoes in their respective regions.
At this time, none of those other observatories are reporting unusual activity or signs of anything more than background noise for now.
According to the U.S. Geological Survey (USGS), there are about 1,500 potentially active volcanoes worldwide, with about 500 of the 1,500 erupting in historical times. Most of the volcanoes in the world are located around the “Ring of Fire” around the Pacific Rim. The Ring of Fire is a region around the rim of the Pacific Ocean where many volcanic eruptions and earthquakes occur. Caused by plate tectonics, lithospheric plates under and around the Pacific Ocean move, collide, and/or are destroyed, creating the seismic activity the Ring of Fire is famous for.
In the U.S., the USGS and volcano observatory units are responsible for issuing Aviation Codes and Volcanic Activity Alert Levels. Aviation Codes are green, yellow, orange, or red. When ground-based instrumentation is insufficient to establish that a volcano is at a typical background level of activity, it is simply “unassigned.” While green means typical activity associated with a non-eruptive state, yellow means a volcano is exhibiting signs of elevated unrest above known background levels. When a volcano exhibits heightened or escalating unrest with the increased potential of eruption, it jumps to orange. Finally, when an eruption is imminent with significant emission of volcanic ash expected in the atmosphere or an eruption is underway with significant emission of volcanic ash into the atmosphere, the code becomes red. Volcanic Activity Alert levels are normal, advisory, watch, or warning. As with aviation codes, if data is insufficient, it is simply labeled as “unassigned.” When the volcano is at typical background activity in a non-eruptive state, it is considered normal. If the volcano exhibits signs of elevated unrest above background level, an advisory is issued. If a volcano exhibits heightened or escalating unrest, a watch is issued while a warning is issued when a hazardous eruption is imminent.