An ash plume rose from Overlook crater at Hawai'i Volcanoes National Park on May 11, 2018. Similar to recent plumes, this event was likely caused by a rockfall from the crater's steep walls, the Hawaii Volcano Observatory reported/U.S. Geological Survey

Fourteen-ton boulders tossed more than a half-mile. Swarms of temblors quaking the East Rift Zone of Kīlauea Volcano at Hawai'i Volcanoes National Park. Dust and ash clouds rising a handful of kilometers into the air, and then raining down on surrounding communities. That explosive eruption was preceded by a draining of magma from a lava lake in the volcano's Halema‘uma‘u crater. That was back in 1924, but Kīlauea's behavior today is eerily similar.

"Volcanic unrest in the lower East Rift Zone of Kīlauea Volcano continues," the Hawaii Volcano Observatory reported Friday evening. "While no lava has been emitted from any of the 15 fissure vents since May 9, earthquake activity, ground deformation, and continuing high emission rates of sulphur dioxide indicate additional outbreaks of lava are likely."

Kīlauea Volcano's recent unrest, which prompted President Trump to declare a state of emergency for the Big Island and led to the national park's nearly complete closure, could be the new normal. And it could get more explosive before the recent episode settles down, according to volcanologists.

To peer into what the volcano's future holds, we can look back to its past. 

Explosive eruption column from Halema‘uma‘u Crater 11:15 a.m. May 18, 1924 - one of many in a series of similar events during May 11-27. Photo from northwest rim of Kīlauea summit, present site of HVO/U.S. Geological Survey

Ninety-four years ago this month, in May 1924, Kīlauea produced its most explosive activity since the early 19th century, according to the Hawaii Volcano Observatory, an arm of the U.S. Geological Survey.

"For 17 days, rocks, ash, and dust erupted in dramatic clouds rising from the crater. Rocks weighing many tons were hurled as far as a kilometer (0.6 mi) from the crater," the observatory's history section notes. "There was some subsidence within Halema‘uma‘u, but the caldera did not deepen appreciably. Within two months, lava reappeared in the crater and above the level of the water table, which inhibited additional large steam explosions. Although the period of explosive eruptions was brief and violent, they were small compared to those between 1500 and 1800."

Prehistoric eruptions of Kīlauea likely sent fountains of bright orange lava 2,000 feet or more into the sky, volcanologists surmise. That far exceeds what we've seen so far this month, with lava fountains of 200 feet or so reported. But more violent activity could be coming in the weeks ahead.

An 8-ton block of rock was tossed out of Kīlauea during the 1924 eruption/U.S. Geological Survey

"Based on this and field observations of the past two days, the lava lake level (in Halema‘uma‘u) continues to drop," the observatory mentioned Friday. "Rockfalls from the steep crater walls have generated small ash clouds mixed with white condensed water vapor intermittently throughout the day. These ash clouds have been relatively low concentration and have risen only a few thousand feet above the ground generating very localized ashfall. More explosive activity generating larger ash clouds remains possible.

"Earthquake activity in the summit remains elevated. Many of these earthquakes are related to the ongoing subsidence of the summit area and earthquakes beneath the south flank of the volcano."

According to the observatory, "(L)ong periods of explosive (tephra-dominated) and effusive (lava-flow-dominated) activity have alternated at Kīlauea for the past 2,500 years. Scientists infer that the eruption style is determined by the amount of magma being supplied to the volcano. When magma supply is high, the summit caldera fills and feeds voluminous lava flows from summit and rift zone vents. When the magma supply drops, the caldera collapses. When the caldera floor is deep enough to be at or near the water table (about 500 m (1640 ft) deeper than present), water can seep into the vent to trigger steam explosions. Eventually magma supply increases, and effusive eruptions dominate as many lava flows fill the caldera and erupt from the rift zones."

Fissure 14 at Leilani Estates near Hawai'i Volcanoes National Park, May 9, 2018/USGS

Road damage from one of the earthquakes associated with 1924 eruption/U.S. Geological Survey

As noted above, the lava lake in Halema‘uma‘u crater has been falling, dropping closer to the water table. Whether it will fall far enough to trigger explosions is difficult to predict, if at all possible. But the volcano's history includes some very potent and deadly eruptions.

"Near the end of this explosive period in 1790, a series of explosive eruptions sent searing pyroclastic surges at least 3.5 km (2.1 mi) down the west side of the summit area," the observatory notes. "This was the deadliest eruption known from a U.S. volcano (but at the time, it was the Hawaiian Kingdom). Several hundred (and perhaps more than a few thousand) people were killed within a few hundred meters of where the Hawaiian Volcano Observatory and the national park's Jaggar Museum are located today. The unfortunate victims died as a result of the hot, ash-rich surge that both suffocated and burned them."

Looking at Kīlauea's history, "scientists conclude that the volcano will eventually return to a long period of mostly explosive activity, just as it did around 1500 CE."

Stream of lava from Pu‘u ‘Ō‘ō flowing through the forest in the Royal Gardens subdivision, February 28, 2008. The lava stream is about 3 m (10 ft) wide. Kīlauea Volcano, Hawai‘i/U.S. Geological Survey

This map shows historic lava flows at Hawai'i Volcanoes National Park/USGS