Eua is a hilly island, the highest peaks are the "Teemoa" (chicken manure) 312 m, with the grave of the soldier on top, and the "Vaiangina" (watersprings) 305 m. The island is not volcanic, but was shaped by the rubbing of the Tonga Plate against the Pacific Plate, pushing Eua up and leaving the Tonga Trench on the bottom of the ocean, a short distance towards the east. The soil of Eua is volcanic, as is that of Tongatapu, but only the top layer, deposited by eruptions of nearby volcanoes ten thousands years ago. Under it are the solid rocks of pushed-up coral. Eua counts many huge caves and holes, not all of which have yet been explored.