Mauna Ulu, Volcanic cone in Hawaii Volcanoes National Park, United States

Mauna Ulu is a volcanic cone within the Kilauea system, located in Hawaii Volcanoes National Park on the Big Island of Hawaii. The ground around it is covered in hardened lava flows, visible channels carved by moving lava, and small secondary craters formed during the eruption period.

Mauna Ulu formed during an eruption on Kīlauea's East Rift Zone that began on May 24, 1969, and ended on July 22, 1974, lasting 1,774 days and producing 350 million cubic meters of lava. At the time it was the longest and most voluminous flank eruption on Kīlauea in at least 2,200 years. The flows covered 44 square kilometers and destroyed parts of what is now Chain of Craters Road, since repaired.

The name Maunaulu means "growing mountain" in Hawaiian, and the U.S. Board on Geographic Names changed the official spelling from Mauna Ulu to Maunaulu in 2015. The cone sits where the eastern rift zone of Kīlauea bends, between the old ʻĀloʻi and ʻAlae craters, and the dormant cone can now be visited.

A marked trail leads through the hardened lava fields to the cone, and the terrain can be hot and exposed depending on the time of year, so sun protection and plenty of water are worth bringing. Conditions in the park can shift quickly, so checking in with a ranger station before heading out is a good idea.

The cone has no tephra layer: scoria thrown from the vent was carried away by the large lava flows, leaving only stacked lava flows in its structure. Steam still rises from fumaroles on the cone, heated by hot rock underground. Hawaii Volcano Observatory instruments on its flanks monitor Puʻu ʻŌʻō.