Here’s the thing about volcano eruptions: It’s really hard to tell exactly when they’ll start, and equally — if not more difficult — to predict when they will be over. And that’s what scientists are saying about the ongoing eruption on Hawaii’s Big Island.

“We don’t have a good idea of how big it is and how long it’ll last,” Tracy Gregg, a geologist who has worked on Kilauea, told The Washington Post. “It could be a couple of days, a couple of weeks. It could be a couple of months. We just have to wait and see.”

Past lava flows from this region suggest the same; they range from days to months and have ejected billions of cubic feet of lava in the process.

2014 — Slow-motion Puu Oo lava flow spares Pahoa

The most recent significant lava flow from the East Rift Zone started in late June 2014, when new vents opened up on the northeast side of the Puu Oo lava cone.

For months, the town of Pahoa watched as the lava crept closer and closer. Lava flowed in and out of cracks in the ground, submerging and resurfacing along a 10-mile-long path to the outskirts of Pahoa village. It stopped short of destroying a waste-recycling center there but continued to be minimally active until early March 2015.

1960 — A tragic case of volcano-meets-civilization

Just like the current eruption, the summit lava lake filled and overflowed in the months leading up to the eruption. Several earthquakes in late 1959 suggested that lava was flowing underground, ready to explode to the surface. On Jan. 12, more than 1,000 earthquakes were recorded with an epicenter just north of Kapoho village. The next morning, the ground had huge cracks through the village, and people knew things had the potential to get much worse.

Hawaii Volcano Observatory scientists described Jan. 12 as “the ground beneath our feet in almost constant motion.” They also heard “low-pitched booming sounds.”

Volcanic vents opened up Jan. 14, spewing lava 330 feet into the air. The lava flow reached the ocean the next day, and in the week that followed, residents of Kapoho tried desperately to divert the lava away from the village. It was about as successful as you would imagine. They built several walls — one as tall as 15 feet — around important facilities like the school, the Coast Guard facilities, homes and a cemetery.

By Jan. 27, lava had swallowed almost all of Kapoho, plus the neighboring village of Koae. The 1960 East Rift eruption was the largest since 1840 at the time.

1955 — A good comparison for 2018

The 1955 eruption is probably the most similar to what’s happening now, according to researchers at the Hawaii Volcano Observatory. It consisted of 24 separate vents along the East Rift Zone and lasted three months. Nearly 4,000 acres were covered in lava, including main roadways, sugar cane fields and residential neighborhoods.

1840 — The largest East Rift eruption we know of

The 1840 eruption along the East Rift Zone was the largest we have record of, in that the lava field generated by it is still visible. Scientists used chemical dating techniques to determine when the lava erupted. Scientists estimate that when the eruption was finished, more than 7 billion cubic feet of lava had poured out from the ground — enough to fill about 35 NFL football stadiums.

Titus Coan, a Christian missionary from New England, arrived on the Big Island just in time for the eruption. An entire chapter of Coan’s “Life in Hawaii” is dedicated to it:

The first eruption from Kilauea which occurred after my arrival in Hilo, began on the 30th of May, 1840. … Imagine the Mississippi converted into liquid fire of the consistency of fused iron, and moving onward sometimes rapidly, sometimes sluggishly; now widening into a lake, and now rushing through a narrow gorge, breaking its way through mighty forests and ancient solitudes, and you will get some idea of the spectacle here exhibited.
During the eruption some of the people of Puna spent much of their time in prayer and religious meetings, some fled in consternation, and others wandered along the margin of the lava stream, at a safe distance, marking with idle curiosity its progress, while others still pursued their daily avocations within a mile of the fiery river, as quietly as if nothing strange had occurred. They ate, drank, bought, sold, planted, builded, slept, and waked apparently indifferent to the roar of consuming forests, the sight of devouring fire, the startling detonations, the hissing of escaping steam, the rending of gigantic rocks, the raging and crashing of lava waves, and the bellowings, the murmurings, the unearthly mutterings coming up from the burning abyss.
Reporter Anna Rothschild explores the science of the Kilauea volcano, and explains why some volcanoes erupt explosively while others are more gentle. (Billy Tucker, Anna Rothschild/The Washington Post)