After weeks of restlessness, Hawaii’s Kilauea volcano erupted explosively Thursday morning, hurling boulders hundreds of feet and sending a towering plume of ash five miles into the pre-dawn sky.

For days scientists had warned about such an eruption, ever since the lava lake that once filled the summit crater began draining back into the ground. Their concern was that steam would form from sinking molten rock interacting with the water table, building pressure inside the volcano until it blasted upward. This phenomenon is known as a phreatic eruption.

How a steam-powered explosive

eruption can occur

The lava lake begins to drain out of the crater at the surface.

As the lava drops below the water table, water in the surrounding rock flashes into steam.

Steam pressure builds, then explodes, blasting out ash and rocks.

How a steam-powered explosive

eruption can occur

The lava lake begins to drain out of the crater at the surface.

As the lava drops below the water table, water in the surrounding rock flashes into steam.

Steam pressure builds, then explodes, blasting out ash and rocks.

How a steam-powered explosive

eruption can occur

The lava lake begins to drain out of the crater at the surface.

As the lava drops below the water table, water in the surrounding rock flashes into steam.

Steam pressure builds, then explodes, blasting out ash and rocks.

How a steam-powered explosive eruption can occur

The lava lake begins to drain out of the crater at the surface.

As the lava drops below the water table, water in the surrounding rock flashes into steam.

Steam pressure builds, then explodes, blasting out ash and rocks.

How a steam-powered explosive eruption can occur

The lava lake begins to drain out of the crater at the surface.

As the lava drops below the water table, water in the surrounding rock flashes into steam.

Steam pressure builds, then explodes, blasting out ash and rocks.

The short-lived episode early Thursday morning was consistent with exactly that kind of eruption. And there may be more to come.

Situated in the southeast part of the Big Island, Kilauea is the youngest in the chain of volcanoes that makes up Hawaii. These volcanoes have formed over millions of years as the Pacific plate drifts over a hotspot in Earth’s mantle.

Kilauea is also the world’s longest active volcano, oozing lava since 1983.

The volcano has two main craters: one at the summit, and one to the southeast, called Puu Oo. In late April, the floor of Puu Oo crater collapsed, and the lava lake within it drained back into the ground.

10 MILES

Hilo

Hawaii

Halemaumau Crater

 

 

Erupted Thursday

MAUNA

LOA

Pu’u O’o

crater

Kilauea

Eruptive fissures

opened on May 3rd

Pacific Ocean

10 MILES

Hilo

Hawaii

Mountain

View

Halemaumau Crater

 

 

MAUNA LOA

Pahoa

(Elevation: 13,677 feet)

Erupted Thursday

Leilani

Estates

Pu’u O’o

crater

Kilauea

(Elevation:

4,091 feet)

Eruptive fissures

opened on May 3rd

Pacific Ocean

10 MILES

Hilo

Hawaii

Mountain

View

MAUNA LOA

Halemaumau Crater

 

 

Pahoa

(Elevation: 13,677 feet)

Erupted on Thursday

Leilani

Estates

Pu’u O’o

crater

Kilauea

Hawaii

Volcanoes

Nat’l Park

(Elevation:

4,091 feet)

Eruptive fissures

opened on May 3rd

Pacific Ocean

10 MILES

Hilo

Hawaii

Halemaumau Crater

 

 

Erupted Thursday

MAUNA

LOA

Pu’u O’o

crater

Kilauea

Eruptive fissures

opened on May 3rd

Pacific Ocean

Scientists expected the molten rock might find a new route to the surface somewhere along the volcano’s east rift zone — an area of weak rock radiating away from the summit. They were right.

In this latest eruptive episode, which began May 3, magma has broken through fissures in the ground and splattered into the air in several residential communities east of the volcano. The flows prompted the evacuation of 1,700 people and destroyed dozens of structures.

Areas where heat was detected

Leilani

Estates

Lanipuna

subdivision

4,000 Feet

Areas where heat was detected

Lanipuna

subdivision

Leilani

Estates

2,000 Feet

Areas where heat was detected

Lanipuna

subdivision

Leilani

Estates

2,000 Feet

Areas where heat was detected

Lanipuna

subdivision

Leilani

Estates

4,000 Feet

But in recent days, the draining lava lake at the main crater drew attention back toward the summit. Hawaii Volcanoes National Park officials said the caldera — the depression at the center of the volcano — dropped more than three feet overnight, triggering frequent earthquakes. The explosion finally occurred at about 4:15 a.m. local time.

The main hazard to people comes mainly from the resulting plume, which is drifting northeast and has dropped ash into nearby communities. Residents should also be aware of vog — a noxious smog formed when sulfur dioxide coming out of eruption vents interacts with oxygen and water vapor in the air.

Video captured two weeks ago on Luana Street within Leilani Estates shows lava fountains as high as 230ft, or 70m, erupting from a fissure.

Kilauea is the youngest of Hawaii's aboveground volcanoes, which have formed over the course of the past 5 million years as the Pacific plate drifts over a hot spot in Earth's mantle. The plume of molten rock rises, then “ponds” in a reservoir 3 miles wide and about 1 to 4 miles beneath the volcano’s summit. As pressure builds in the magma chamber, the magma seeks out weak spots in the surrounding rock, squeezing through the earth until it finds a vent to the surface.

The motion of all that magma triggers earthquakes. Since April 30, USGS sensors have detected more than 2,626 temblors — including one with a magnitude of 6.9, the strongest to hit the island in more than four decades.

Earthquakes

April 30 to May 7

Kohala

6.9 magnitude

May 4

Mauna Kea

Hualai

HAWAII

Mauna Loa

Kilauea

5.4 magnitude

May 4

5.3 magnitude

May 5

20 miles

Circles sized according to the amount of

energy released

Earthquakes

April 30 to May 7

Kohala

6.9 magnitude

May 4

Mauna Kea

Hilo

Hualai

HAWAII

Kailua

Pu’u O’o

crater

Leilani

Estates

Mauna Loa

Kilauea

5.4 magnitude

May 4

5.3 magnitude

May 5

20 miles

Circles sized according to the amount of energy released

Tracy Gregg, an associate professor of geology at the University of Buffalo who has worked on Kilauea, said the fact that there are still eruptions from so many new fissures forming suggests the lava is from a new batch of magma rising from deep within the volcano.

May 3:

Fissures

appear.

May 1:

Lava lake

begins to drop.

April 30:

Crater floor

collapsed.

 

Kilauea

Halemaumau

Crater

Pu’u O’o

Detail below

10 MILES

Thermal images

of Halemaumau

lava lake

May 6

May 2

May 8

May 4

Thermal

images of

Halemaumau

lava lake

May 2

May 4

May 6

May 8

Kilauea

May 3: Eruptive

fissures appear

Halemaumau Crater

May 1: Lava lake has

significantly dropped

from the crater rim.

April 30:

Pu’u O’o crater

floor collapsed

 

NORTH

5 MILES

Pacific Ocean

Thermal images of

Halemaumau

lava lake

May 2

May 4

May 6

May 8

Kilauea

April 30:

Pu’u O’o crater

floor collapsed

 

May 3:

Eruptive

fissures

appear

Halemaumau Crater

Shown above in a series of

thermal images, the lava lake

has significantly dropped

from the crater rim.

NORTH

5 MILES

Pacific Ocean

May 1:

Lava lake

begins to drop.

April 30:

Crater floor

collapsed.

 

May 3:

Fissures

appear.

Kilauea

Halemaumau

Crater

Pu’u O’o

Detail below

10 MILES

Thermal images

of Halemaumau

lava lake

May 6

May 2

May 8

May 4

Aaron Steckelberg, Monica Ulmanu and Tim Meko contributed to this report

About this story

Originally published May 7, 2018.

May 6 aerial imagery by Bruce Omori/Paradise Helicopters/EPA-EFE/SHUTTERSTOCK. May 6 thermal image from USGS Hawaii Volcano Observatory.

Satellite imagery DigitalGlobe via GoogleEarth. Street-level data from Maps4News/HERE.

Video by Bruce Houghton, USGS and University of Hawaii

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