Lava first reached the sea Friday night, and peaked Saturday night and Sunday morning, with open cascades visible, said Don Swanson, a geologist with the U.S. Geological Survey's Hawaiian Volcano Observatory.

By yesterday morning the activity had shifted mostly to an underground tube system.

"At the front of the new delta that is forming, there were a number of new entry points that were very colorful, but there was just a trickle going over the sea cliff because most of the lava is hidden by the crust of the tube," Swanson said.

Pahoehoe swirls form along the east edge of the flow near the ocean, and lava emerges from under the crust and plunges over the old sea cliff in this photo taken Saturday. National Parks Service photos

The new flow added a coating of lava several yards thick on top of an existing lava delta at the Lae'apuki area, and created a new delta that is 250 to 300 feet long, Swanson said.

From the ranger hut at the end of the Chain of Craters Road to the Lae'apuki coastal area where the flow is entering the ocean is a hike of about 2.8 miles, but park ranger Mardie Lane urged visitors to be cautious.

Rangers are staffing the area all day and into each evening, and Lane advised anyone considering the hike to talk to a ranger and familiarize themselves with the hazards.

"We don't recommend it, but if you're intent on doing it, we're here to help you do it safely," she said.

For those not up to the hike, Swanson said observers with binoculars can get a good view of the glow from pulloffs near the bottom of the Chain of Craters Road.

Lane said rangers also have located high ground near the end of the road that offers good viewing of the steam plume, and in some cases lava can be seen in the distance dropping into the sea.

"Of course, everything is subject to the whim of nature, and so what happens today may or may not happen tomorrow," she said. "That's just the unpredictability of Pele."