makatea islands. Examples include Makatea itself
(Tuamotu archipelago), Atiu (Cook Islands), and
most of the inhabited islands of Tonga. This is an
important class of islands. They are characterized
by rocky coralline substrates, but some are partly
volcanic. Many have had commercially exploitable
deposits of phosphate (guano) formed through the
ages from droppings of seabirds (e.g. Nauru; see
Chapter 12). For a discussion of the complexities of
volcanic, limestone, and makatea (composite)
island landscapes, see Nunn (1994).Climatic characteristics
Island climates have, self-evidently, a strong oceanic
influence, and quite often are considered anomalous
for their latitude, as a consequence of their location
in the path of major ocean- or atmospheric current
systems (e.g. the Galápagos; Darwin 1845). Low
islands tend to have relatively dry climates. High
islands tend to generate heavy rainfall, although
they may also have extensive dry areas in the rain
shadows, providing a considerable environmental
range in a relatively small space. Even an island of
only moderate height, such as Christmas Island
(Indian Ocean), with a peak of 360 m and general
plateau elevation of only 150–250 m, benefits from
orographic rainfall, allowing rain forest to be sus-
tained through a pronounced dry season (Renvoize
1979). Islands may also be expected to receive rain-
fall that has a generally different chemical content
than that experienced over continental interiors (cf.
Waterloo et al. 1997).
As noted by J. D. Hooker in his lecture to the
British Association in 1866, the climate and biota
of islands tend to be more polar than those of
continents in the same latitude, while intraannual
temperature fluctuation is reduced (Williamson
1984). Islands near the equator frequently exhibit
annual average temperature ranges of less than
1 C, and even in temperate latitudes, the annual
average ranges are less than 10C: for example, 8C
in the case both of Valentia (Ireland) and the Scilly
Isles. Some islands do, however, experience quite
large interannual variations in other features of their
weather. Variability in rainfall, for example related34 ISLAND ENVIRONMENTS
Table 2.4Area and relief of New Zealand and neighbouring
islands (from Mielke 1989, Table 9.1)
Island Area (km^2 ) General relief
South Island 148 700 50 peaks over 2750 m
North Island 113 400 Three peaks over 2000 m
Stewart 1720 Granite; three peaks, up to 987 m
Chatham 950 Cliffs to 286 m
Auckland 600 Volcanic; one peak 615 m
Macquarie 118 Volcanic; 436 m, glacial lakes
Campbell 113 574 m, glaciated
Antipodes 60 Volcanic; peak of 406 m
Kermadec 30 Volcanic; peak of 542 m
Three Kings 8 Volcanic
Snares 2.6 Granite; cliffs to 197 m
(a)(b) Planeze(c)(d)Figure 2.15Stages in the erosion of a volcano (after Nunn 1994,
based on an original in Ollier 1988). (a) An intact volcano, with radial
grooves (e.g. Tristan da Cunha); (b) Planeze stage, in which some of
the radial drainage channels have undertaken headwall capture,
leaving triangular-shaped remnants relatively untouched by fluvial
erosion (examples can be seen on St Helena); (c) Residual volcano,
where planezes have been removed by erosion, but the original form
of the volcano is still evident (examples can be seen in the Canaries
and Cape Verde islands); (d) Volcanic skeleton, where only the necks
and dykes remain as prominent features (e.g. Bora-Bora, French
Polynesia).