罗希海底山是位于夏威夷岛东南方约35公里处的一座仍活跃的海底火山。此火山与冒纳罗亚火山（世界最大型的盾状火山）相邻。

罗希海底山是夏威夷-天皇海山链（长达5,800公里，自罗希以及夏威夷岛西北方一路延伸的火山岛链）中最新形成的一座火山。此山与夏威夷-天皇海山链的火山都属于热点火山，并且距离板块边界非常遥远，很不同于许多在环太平洋火山带使太平洋的板块边缘活动剧烈的其他火山。

夏威夷群岛的火山都来自于夏威夷的热点，而罗希海底山是夏威夷火山中最新形成、尚在海底盾前阶段的地质型态。

罗希大约在400,000年前开始成形，预估10,000－100,000年后将会升越海平面。此山的高度（自海底至水下山顶的长度）超过3,000米，比圣海伦斯火山（此山最著名的1980年喷发导致了美国本土记录中最大的一次火山爆发）还要高。用华人较熟悉的山岳来做比喻，罗希海底山的高度比阿里山还高。

Lōʻihi Seamount (also known as Loihi) is an active submarine volcano located about 35 km (22 mi) off the southeast coast of the island of Hawaiʻi. The top of the seamount is about 975 m (3,000 ft) below sea level. This seamount lies on the flank of Mauna Loa, the largest shield volcano on Earth. Lōʻihi, meaning "long" in Hawaiian, is the newest volcano in the Hawaiian-Emperor seamount chain, a string of volcanoes that stretches over 5,800 km (3,600 mi) northwest of Lōʻihi. Unlike most active volcanoes in the Pacific Ocean that make up the active plate margins on the Pacific Ring of Fire, Lōʻihi and the other volcanoes of the Hawaiian-Emperor seamount chain are hotspot volcanoes and formed well away from the nearest plate boundary. Volcanoes in the Hawaiian Islands arise from the Hawaiʻi hotspot, and as the youngest volcano in the chain, Lōʻihi is the only Hawaiian volcano in the deep submarine preshield stage of development.