0198566123.pdf

The last 2 million years has been a period of
great environmental dynamism in the Canaries.
Volcanic mountain building activity has con-
structed the two westernmost islands, La Palma
(1.5 Ma) (Fig. 2.9e) and El Hierro (1.1 Ma). Both
have been prone to catastrophic landslides, related
principally to the instability of their high volcanic
summits. The last of them (El Golfo in El Hierro)
occurred as recently as 15 000 years ago, cutting
away the northwest half of the island, and distrib-
uting it across some 1500 km^2 of the ocean floor
(Canalset al. 2000).
It is only within the last 1.5 Ma that the great
acidic volcanic cycle of Las Cañadas unified the old
basaltic massifs of Teno, Adeje, and Anaga into
today’s Tenerife. The new land surface enabled
enhanced biotic exchange between the old massifs.
Several landslides (Icod, Las Cañadas, La Orotava,
Güímar) followed the construction of this edifice,
having catastrophic effects on both Tenerife and the
nearby islands. The building of the Teide stratovol-
cano is very recent, with its highest tip (3718 m)
being built in the prehistoric period, approximately
800 years ago. Such events leave their imprint on
the genetic architecture of lineages, through
repeated subdivision of formally contiguous popu-
lations (e.g. Moya et al. 2004).
Finally, some 50 000BP, the small islets north of
Lanzarote (La Graciosa, Montaña Clara, and
Alegranza) and Fuerteventura (Lobos) were built,
giving the Canary archipelago its present shape
(Fig. 2.9f). With the exception of La Gomera, which
has been dormant for some 2–3 Ma, the islands
have remained active, with some 15 volcanic erup-
tions in Lanzarote, Tenerife, and La Palma in the
last 500 years (Anguita et al. 2002).
In addition to the building, collapse, and erosion
of the islands, eustatic sea-level changes during the
Pleistocene have alternately doubled and halved
the emerged area of the archipelago, from approx-
imately 7500 km^2 during interglacials to some
14 000 km^2 during stadials (García-Talavera 1999).
During low sea-level stands, such as coincided
with the peak of the last Ice Age c.13 000BP, the
islands were about 130 m higher in altitude.
Lanzarote and Fuerteventura were joined together,
along with nearby islets, into a single large island

(Mahan,c.5000 km^2 in area). The shortest distance

from the archipelago to the African mainland was

reduced from about 100 km to 60 km, the present-

day submarine bank of Amanay, north of Jandía,

formed an island of some 100 km^2 (Fig. 2.10), and a

‘stepping-stone’ corridor of islands provided

enhanced connectivity between the Canaries,

Madeira and the Iberian Peninsula (Fig. 2.11).

Hawaii

The Hawaiian chain is characterized by the growth

of shield volcanoes that go through a known life

cycle, with four well-defined stages (Wilson 1963;

Price and Clague 2002):

ENVIRONMENTAL CHANGES OVER LONG TIMESCALES 29

Salvages

R. Famara

Concepción

Amanay

PALAEOCANARIES (~18kyBp)

Mahan

PRESENT AFRICA

AFRICA

95 km

60 km

Salvages

Figure 2.10The Canaries at the time of the sea-level minimum of

the Last Glacial period and in the present day (Modified from

García-Talavera 1999).