"Henderson is an elevated limestone island situated in 24"22'S and 128°20'W. Its nearest neighbours are , 200 km to the west-southwest; , 200 km to the west; and , 360 km to the east. It rises as an isolated conical mound from depths of ca 3.5 km, on a trend line which continues that of the and eastward to Ducie, and is presumably a reef-capped volcano. The island has a greatest length of 9.6 km and greatest width of 5.1 km, based on the ; its area is 37 sq km. It is usually said to rise about 33 m (100 ft) above sea level. ... The top of the island, as well as any land at the bases of the cliffs, is densely vegetated by tangled scrub and scrub-forest, but the central part of the depression and the makatea are more sparsely covered. In places, where the forest is taller and the canopy more complete, it is possible to walk freely for short distances. The tallest trees are ' , which in places rises as an emergent above the general canopy. The crowns of such emergents are conspicuously pyramidal or conical. The dried fallen leaves of Pandanus cover the ground in many places. The scrub and much of the scrub-forest is in many areas so dense and tangled that walking through it is impossible without the constant and vigorous use of a machete, and exhausting and slow even with the use of one. ... Fresh water is almost entirely absent. Slight dripping has been observed from the roofs of certain caves."