It lies about 6 km (3.7 mi) north of Tofua island and reaches 1,030 m (3,379 ft) above sea level, the highest point in Tonga.

Although Kao does not display fresh-looking lava flows, it is likely very recent in origin due to the absence of deep gullies or high sea cliffs.

The slopes of the island rise at angles exceeding 35 degrees to the summit, which has a series of small volcanic craters.

The island is densely jungled on its lower flanks, interspersed with thick chest-height ferns that are virtually impassable to all but the most determined trekkers armed with machetes and a good deal of stamina.

It shone so brilliantly that the Samoan deities were struck with fear, thinking that the sun was rising and that their dastardly work was about to be revealed.