The explosive history of Kilauea is not well known. Today, it’s renowned for lobes of slow-moving, calm lava, which ooze out of cracks in the flanks of the volcano, pour downslope and eventually flow into the sea, where the lava cools and gradually enlarges the island. But in the past, Kilauea has erupted violently — more often and for much longer periods than was previously thought. Now, researchers have learned that over the past 2,500 years, violent eruptive periods lasting centuries have alternated with periods of quiet flows. Once an explosive period has begun, conditions on the Big Island will be very different from those on which the past hazard assessment was based.