Off the coast of the Big Island of Hawaii, lava is flowing into the ocean like blood from a ruptured artery. From the Kilauea volcano's Kamokuna ocean entry, it hits the salty water and explodes. Molten rock shoots upward and outward. A steamy cloud of acid rises from below. Beneath the ocean's surface, lava cools. Rubble forms.

Normally it stacks up, creating a rocky shelf on which the lava settles: a lava delta. But this time, the flow has continued to gush for an entire month.

This same volcano has sent lava traveling through tubes from moving vents along its eastern rift zone, Pu'u O'o, ever since it erupted 34 years ago. And these tubes have carried lava to a number of spots along the ocean. But such streams usually last just a day or two; this one has been going since New Year's Eve, when 21 acres of lava delta collapsed into the ocean, exposing the tube.

"The only thing we can surmise is the offshore topography apparently is so steep that, as the lava is flowing in and forming all this new rubble, it's just slipping down into deeper parts of the ocean and not piling up to form a new delta," said Janet Babb, a geologist at the U.S. Geological Survey Hawaiian Volcano Observatory, who monitors the volcano. "Lava will continue to flow into the ocean until it's disrupted."

That means the supply must be cut, either from the source, or by a large earthquake that would crimp or collapse the tubes that are carrying it.

This spectacular lava flow into the ocean garnered national attention when it showed up in photos and videos on social media this week, but it started moving long before that.

In May, a new vent broke out on Pu'u O'o. Lava started flowing and moving south toward the coast. As the lava moved, the part touching the air cooled and crusted over, resulting in lava tubes that made its passage to the ocean far more efficient, just as veins channel blood. The tubes from this volcano range in diameter: so fat that a bus could pass through, so skinny that a human couldn't.

When 2,100-degree hot lava hits salty water it results in a chemical explosion that sends rock, glass and fragments of molten lava called spatter onto the land and out to the sea.

"Until it starts piling up to form a new delta," Babb said, "this is what we have."