There are 3 general classifications that define a volcano’s state of activity.
This means that the volcano is alive and kicking. It could be currently erupting, or showing signs of unrest. There could be earthquakes or an increase in volcanic gasses. But sometimes these symptoms aren’t obvious. If the volcano has erupted within the last 10,000 years, or within historic times, it is considered to be active. Now, 10,000 seems like a long time to us mere mortals, but in geologic years, that’s pretty recent.
This means that the volcano is sleeping and is showing no signs of unrest (aside from the occasional snore). It hasn’t erupted in the past 10,000 years, but it is expected to erupt again. So don’t get too cozy.
This means that the volcano is not expected to erupt ever again. It has been an extremely long time since its last eruption (a million years give or take a millennia), and it has disconnected from the source that was fueling the eruptions in the first place. However, nature always loves a surprise party and there have been a few extinct volcanoes that have woken up and started to erupt again.
It’s never black and white with these classifications. For example, Yellowstone is considered an active volcano. You can tell just by looking at the steaming landscapes and spectacular geysers, but it hasn’t blown chunks of rock sky high in about 640,000 years. So it blurs the line a little bit.
There are a few other volcanoes out there like Yellowstone – that haven’t erupted in many moons, yet they are considered active. These three classifications don’t really get down to the nitty gritty of each situation, but they’re generally a good rule of thumb when trying to figure out if you’re climbing on a sleeping giant… or not.
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