of dissection. More recently, Menard (1986) com-
pared the values resulting with the ages determined
by potassium–argon dating (up to an age of 1.6 mil-
lion years), thus demonstrating that dissection is
indeed a function of age of the volcano. Height of
island can be important in respect to changes in sea
level, receipt of rainfall, and to other climatic char-
acteristics. In addition, large, high volcanic islands
are subject to periodic catastrophic landslips, which
can radically reshape substantial areas of the island
(Hürlimannet al. 2004; below).
Coral or limestone islands and atolls tend to be
very low-lying and flat. There are clear implica-
tions here with respect to future sea-level changes
(Chapter 12). Those which have been uplifted to
more than a few metres above sea level are termedTHE PHYSICAL ENVIRONMENT OF ISLANDS 33Eocene 48Ma Early Miocene 20MaOligocene 38Ma Late Miocene 10MaJACACU
NH
PRMXSAJAJASHSHNHNHPRPRLALASASACACAMXMXNH PR
SHCUJAMXCUCU(a)(b)(e)(d)(c)50 40 30CubaPuerto Rico20 10Million years before presentCosta Rica - PanamaJamaicaHonduras - Nicaragua
Mexico - YucatanSouthern HispaniolaNorthern HispaniolaLesser Antilles
South AmericaCentral AmericaAmericaWestern S.Figure 2.14Hypothesized configurations of the Caribbean area during the past 50 million years. (a–d) Maps of changing positions. Present-day
land outlines are used for ease of recognition and do not indicate shorelines of the time. CACentral America, MXMexico, JAJamaica,
CUCuba, NHnorthern Hispaniola, SHsouthern Hispaniola, PRPuerto Rico, LALesser Antilles, SASouth America. (e) Simplified
scheme showing the relative positions of the land areas, increased distance apart indicating increased barriers to dispersal. Areas that were
largely inundated are designated with water wave symbols. (Redrawn from Buskirk 1985, Figs 2 and 4.)