Environmental Engineering Reference
In-Depth Information
2
GeoloGical conTeXT
converge on the central part of the island. eruptive
activity at Mount izaña, where el Teide observa-
tory is located, ceased more than 300 ka (edgar
et al. 2007), whereas recorded eruptive activity in
Tener-ife has consisted of six strombolian eruptions,
namely siete Fuentes (1704), Fasnia (1705), arafo
(1705), arenas negras (1706), chahorra (1798) and
chinyero (1909). The last three eruptions occurred
at the nW ridge, the most active area of the island,
together with el Teide-Pico Viejo complex, for the
last 50,000 years (carracedo et al. 2007).
2.1
Tenerife
Tenerife is the largest island of the canarian archi-
pelago and one of the largest volcanic islands in the
world. it is located between latitudes 28-29°n and
longitudes 16-17°W, 280 km distant from the afri-
can coast. The morphology of Tenerife (see
Fig. 1
)
is the result of a complex geological evolution:
the emerged part of the island was originally con-
structed by fissural eruptions that occurred between
12 and 3.3 Ma (ancochea et al. 1990). in the central
part of the island, where the observatory is located,
the emission of basalts and differentiated volcanics
gave rise to a large central volcanic complex, the
las cañadas edi-fice, that culminated in the for-
mation of a large elliptical depression measuring
16 × 9 km
2
, known as las cañadas caldera (Martí
et al. 1994). in the northern sector of the caldera,
the Teide-Pico Viejo complex was constructed as
the product of the most recent phase of central vol-
canism. Teide-Pico Viejo is a large stratovolcano
that has grown during the last 175 ka. The basaltic
activity, which overlaps the las cañadas edifice, is
mainly found on two ridges (ne and nW), which
2.2
La Palma
The island of la Palma is the fifth in extension
(706 km
2
) of the canary islands and the second in
two main stages of the development of oceanic volca-
noes, the submarine and subaerial stages, outcrop in
la Palma, since the submarine basement or seamount
that was built during the Pliocene (4 to 2 Ma) were
uplifted up to 1.3 km above the present sea level
(ancochea et al. 1994). The subaerial edifice is
conformed by a series of overlapping volcanoes
(navarro & coello 1993): (1) the northern shield
of the island includes the Garafía shield volcano
(1.7 to 1.2 Ma), the Taburi-ente shield volcano (1.1
to 0.4 Ma) and the Bejenado edifice (0.55 to 0.49
Ma); the caldera de Taburiente, in the center of
the old shield, and cumbre nueva ridge formed
by a combination of large landslides and erosion;
(2) The cumbre Vieja Volcano (0.4 Ma to present)
in the southern half of the island. The cumbre
Vieja ridge is interpreted to be a volcanic rift zone
because of the prominent north-south alignment
of vents, fissures and faults. historic eruptions
on la Palma have lasted between 24 and 84 days
and were recorded in 1470/1492 (uncertain), 1585,
1646, 1677-78, 1712, 1949 and 1971 (Romero-Ruiz
1991). The Roque de los Muchachos observatory
is located atop the Taburiente edifice, at the rim
of the caldera de Taburiente, and hence eruptive
activity in the proximity of the observatory ceased
more than 0.4 Ma ago.
Figure 1. simplified shaded-relief map of central chile
and the islands of Tenerife, la Palma and hawaii, indi-
cating the most important geological features (see text
for details). The filled circles of different sizes and col-
ours indicate the location, magnitude and depth of the
earthquakes registered during the period 1973-2008. The
location of the observatories are indicated by black filled
circles. in Tenerife, the region surrounded by the black
solid line and the dark areas indicate the regions affected
by recent (last 10 ka) and historical (last 500 years)
volcanic activity, respectively. in la Palma, the region
surrounded by the thick solid line indicates the region
affected by recent and historical activity of cumbre Vieja
volcano. in chile, the location of the Peru-chile trench is
indicated by a white solid line, whereas the volcanic arc is
shown as filled black triangles.
2.3
Hawaii
The island of hawaii is the youngest island in
a chain of volcanoes that stretches about 5600
kilometres across the northern Pacific ocean. The
island chain results from a magma source that
originates deep beneath the crust. The ocean crust
and lithosphere above the magma source, within
the Pacific tectonic plate, move to the northwest
with respect to the deep stationary magma source.
over a span of about 70 million years, new island
volcanoes are formed and older volcanoes are
carried away from the magma source, erode, and
