Over the weekend, Mauna Loa, the world's largest active volcano, erupted for the first time in 38 years.As of Monday evening, much of the lava from the eruption was contained to the mountain's caldera, a large crater near the peak. No communities are at immediate risk from the eruption, but people in Hawaii are preparing for falling ash. The mammoth volcano makes up a majority of the big island of Hawaii. The island chain's main eight islands are home to 15 different active volcanoes. Sunday night's eruption was the first major activity at Mauna Loa in the past 38 years. USGS geologist Andy Calvert said that gap isn't unusual.“That’s how Mauna Loa behaves. It will be quiet most of the time. And then it will have some sort of seismic crisis uptick that lasts for kind of days, weeks, months and then it goes quiet again," Calvert said.Globally, there are 1,300 active volcanoes, including several in Northern California. Though, Calvert says the word "active" is more based on semantics than anything."They're very much asleep at this point," Calvert said. According to the U.S. Geological Survey, Mount Shasta, Lassen and Medicine Lake Volcano have all erupted within the past 3500 years and are poised to erupt again in the future. Lassen Volcanic National Park's main peak erupted in 1921. This is the most recent known eruption in the state.While scientists can't precisely predict where and when the next major volcanic eruption will occur, they can look for warning signs by following seismic activity. An uptick in earthquake activity was reported in the months leading up to the recent eruption at Mauna Loa.Calvert said the connection between seismic activity and volcanic activity has to do with magma shifting deep below Earth's surface, breaking rocks as it moves. We feel that breakage as a seismic wave.The USGS has all relatively recent U.S. volcanoes monitored. Were any to threaten imminent eruption, they would know about it well ahead of time.