The Big Island of Hawaii is still growing, driven mainly by a slow volcanic eruption that hasn't stopped since 1983. Lava from the Kilauea volcano normally flows south toward the sea, but Pele — the Hawaiian volcano goddess who is believed to live inside Kilauea — can be hard to predict.

Kilauea lava has occasionally flowed northeast in recent years, including an ongoing flow that began on June 27, 2014. That lava has now moved far enough inland that scientists have upgraded a volcano "watch" to a "warning," and the island's mayor has declared a state of emergency. Moving at an average rate of 820 feet per day, the lava may enter a residential neighborhood in less than a week.

"We project the lava could reach the boundary of the Kaohe Homesteads subdivision within 5-7 days should the lava resume advancing within the crack system," according to a Sept. 4 report from the Hawaiian Volcano Observatory (HVO). No evacuation has been ordered as of Sept. 5, but the emergency declaration is meant to keep roads clear if residents suddenly do need to flee.

"We are taking this step to ensure our residents have time to prepare their families, their pets, and their livestock for a safe and orderly evacuation from Ka'ohe in the event the flow continues to advance," Hawaii Island Mayor Billy Kenoi said in a statement issued Sept. 4.

Kilauea lava

This thermal image shows heat from the underground lava tube that's feeding Kilauea's recent surface flows. (Photo: HVO)

Kilauea volcano

A "skylight" reveals the fluid lava stream within the main tube of Kilauea's latest lava flow, which began June 27. (Photo: HVO)

Forecasting the flow of lava can be tricky, the HVO explains, since it's influenced by subtle quirks of topography as well as variations in lava volume. It's also moving above and below ground through a network of cracks in the terrain, complicating efforts to track its speed and direction.

"There continues to be some evidence of subsurface flow activity with noted by steam plumes being emitted from the crack system," the Hawaii County Civil Defense reported in a Sept. 4 bulletin. "The surface flow is moving very slowly and does not pose an immediate threat to area residents. The surface flow is located approximately .8 miles southwest or upslope of the Wao Kele Puna Forest Reserve boundary and moving in an east/northeast direction."

Kilauea's oozy, slow-moving lava has inundated residential areas several times during its current 31-year eruption. It repeatedly did so between 1983 and 1990, destroying 182 homes, Hawaii's oldest temple, miles of public highway and a visitor center at Hawaii Volcanoes National Park. Lava flows briefly entered the village of Kalapana in 1986, then pushed through the entire community in 1990.

It remains unclear how far Kilauea's latest flow will go, but it's also not the only volcanic threat on the Big Island. Mauna Loa, Kilauea's much larger neighbor, sent lava near the major city of Hilo when it last erupted in 1984. It's still active, and its history of big eruptions combined with its proximity to dense populations has earned it a spot on the list of "Decade Volcanoes" — 16 volcanoes around the world deemed especially dangerous to people by an international panel of scientists.

Despite their knack for destruction, however, volcanoes are also what created Hawaii from scratch. Kilauea is still building the Big Island, for example, adding more than 500 acres of new land since 1983. And 15 miles to the southeast, an underwater volcano named Loihi is slowly building the next Hawaiian island, which is expected to rise up from the Pacific Ocean in about 250,000 years.

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Russell McLendon ( @russmclendon ) writes about humans and other wildlife.