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January 3, 2024

All's quiet on the volcano front in California for the New Year. But what does it mean when we say a volcano is 'quiet' or at 'background levels of activity' versus experiencing 'unrest'?

Volcanoes are noisy, gurgly, shifty places. As magma and fluids and gases move, settle, and cool, the crust around them rattles, rumbles and heaves. To tell the difference between normal and unusual, volcanologists first need a long-term record of this behavior. For example, how many earthquakes a volcano has in a week, if those earthquakes come in swarms, if the volcano deforms and how much, or how much and what kind of gas it releases.

Titanium tubed used to collect gas from a fumarole near Lassen Peak, California
Titanium tubed used to collect gas from a fumarole near Lassen Peak, California.

Ideally collected over multiple years, a long-term record makes it apparent when something changes. Because it takes a while to build toward eruptions, volcanoes will usually give plenty of warning signs that something is happening - the 'unrest' we refer to in our updates. Unrest can take place over weeks, months, or even years before an eruption happens. Sometimes unrest can happen without an eruption at all, like the 1980 earthquake activity in Long Valley, where an intrusion of magma created dramatic earthquakes and ground deformation.

Spotting unrest to an eruption is why we have monitoring networks with multiple kinds of instruments on volcanoes. Catching early signs of unrest means that USGS scientists will have the maximum amount of time to add more instruments, interpret activity, and communicate volcanic hazards to nearby communities.

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