Lava from Kilauea’s summit lava lake spilled out of its Overlook crater onto the floor of Halemaumau Crater on Monday, resulting in the largest overflow since the summit vent opened up 10 years ago.

The overflow was the largest of four pulses from the lava lake that escaped onto the crater floor since late Sunday night, Hawaiian Volcano Observatory scientists said Monday.

In addition, scientists noted a small overflow of the south crater rim at around midnight Saturday.

While the lava lake dropped in level Monday afternoon, the overflows represent the latest signs of potential heightened activity at Kilauea volcano.

Last week the Hawaiian Volcano Observatory issued a volcano activity notice warning of the potential for a new vent and lava flow at Puu Oo or along Kilauea’s East Rift Zone.

The notice said the magma system beneath Puu Oo had become increasingly pressurized, leading scientists to think a new vent could open up soon.

Earlier, officials noted that the summit lava lake was at its highest level in more than a year.

“What’s going on? We don’t know for sure,” said Janet Babb, Hawaiian Volcano Observatory geologist.

There could be an increased magma supply in the volcano’s storage system, Babb said, or there could be some kind of backup in the storage system. Bottom line, she said, is that it’s hard to say.

The summit lava lake last overflowed in October 2016. It also overflowed in April and May 2015, when 37 acres of the 130-acre Halemaumau Crater floor were covered by new lava.

This week’s overflows represent the third time the summit’s lava lake has risen high enough to spill out onto the crater floor.

After lava briefly moved onto the Halemaumau floor around midnight Saturday, there were four more pulses late Sunday and early Monday. The largest one occurred during the fourth pulse, starting at 6:30 a.m. and continuing for about three hours.

The flow left a shiny black lava covering over an estimated 39 acres, or roughly a third of the crater floor.

The area around Halemaumau remains closed to the public due to the ongoing volcanic hazards, including elevated sulfur dioxide gas emissions and possible rockfalls and explosions.

Over at Puu Oo, a tiltmeter and GPS station have recorded inflation since about mid-March, and recent webcam images have recorded an uplift of the crater floor by several yards. It also appears that magma is accumulating at shallow depths beneath the cone, officials said.

“We’re keeping a close watch on Puu Oo,” Babb said.

A new vent soon could form because similar episodes of inflation and uplift at Puu Oo preceded the volcano’s last vents that opened up, officials said.

In May and June 2014 similar inflation was recorded prior to a June 27 flow that ended up threatening Pahoa. And in May 2016 there was uplift before a new flow started that is still active above Pulama pali and does not pose a threat to any communities.

When Hawaiian Volcano Observatory issued its volcano activity notice last week, it was the first time the outpost of the U.S. Geological Service had ever produced a formal warning about a possible new vent, said Steven Brantley, deputy scientist in charge at the observatory.