A third lava flow from Hawaii's erupting Kilauea volcano streamed into the ocean on Thursday as U.S. Marine Corps helicopters stood by to evacuate a Big Island community should molten rock or huge cracks block its final escape route.

Six huge fissures sent rivers of molten rock through a blackened, volcanic wilderness that was once jungle, farmland and rural homes.

Kilauea, one of the world's most active volcanoes, entered the fourth week of what may be an unprecedented, simultaneous eruption at its summit crater and along a six-mile (9.7-km) string of fissures 25 miles (40 km) down its east flank. At about 6 p.m. local time on Thursday, the volcano erupted at its summit, sending ash 10,000 feet (3000 m) into the air. The wind may carry ash to the southwest toward the Pahala area, the Hawaiian Volcano Observatory said.