Santa Isabel, Bioko Island, Equatorial Guinea, Africa
Location: 3.58N, 8.75E
Elevation: 3,007 m
Landsat image of Santa Isabel processed by Sarah Sherman, April 2000.
Bioko (formerly called Fernando Poo) is one of the four volcanic islands
that comprise the small nation of Equatorial Guinea in the Gulf of Guinea.
The shield volcano Santa Isabel makes up all of Bioko. As the Landsat image
shows there are two overlapping calderas at the summit of Santa Isabel,
both of which open to the NW. Probably erosion from tropical rains cut the
downslope walls of these calderas. To the east of the calderas, a diagonal
dark line marks the edge of a small fault--apparently the area between the
fault and the calderas has sunk slightly making a linear depression called
a graben. A line of small, recent-looking cinder cones cross the graben.
According to the Smithsonian Institution, three eruptions have occurred on
the flanks of Santa Isabel, in 1898, 1903, and 1923. Very little is known
geologically about this island or the eruptions.
Bioko and the other three islands in the Gulf of Guinea extend a 400 km line
of volcanoes on the nearby continent of Africa. This alignment is called the
Cameroun Volcanic Line, after the most famous of its volcanoes, Mt. Cameroun.
The island is home to seven species of endangered primates and three species of galagos. Additionally, there are sea turtles and 200 species of
birds. The island has been home for 3,000 years to the Bubi tribe, which
evolved independent of outside influences until the last few hundred years.
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