A small earthquake rocked an extinct submarine volcano west of Hawaii island late Wednesday night.

The magnitude-2.8 quake, which struck at 10:40 p.m., had an epicenter in the ocean 28 miles north-northwest of Kailua-Kona, according to the U.S. Geological Survey.

That places it on the flanks of the submarine volcano known as Mahukona.

University of Hawaii geologist Mike Garcia and colleagues have called Mahukona “the missing Hawaiian volcano” in that it fills in the previously assumed gap between Hualalai on Hawaii island and Kahoolawe as the chain developed on roughly parallel tracks. Garcia says it went extinct about 500,000 years ago, “perhaps before reaching sea level.”

The paired sequence of volcanoes was probably caused by a split of the Hawaiian mantle plume during its ascent, creating two primary areas of melting 20 to 25 miles apart that have persisted for at least the last 4 million years, the researchers say.