Environmental Engineering Reference
In-Depth Information
Volcanic dikes engineering properties for storing and regulation
of the underground water resources in volcanic islands
J.c. santamarta cerezal
Escuela Técnica Superior de Ingeniería Civil e Industrial, Universidad de La Laguna (ULL)
Avenida Astrofísico Francisco Sánchez, La Laguna, Tenerife, Spain
l.e. hernández
Consejería de Obras Públicas y Transportes, Gobierno de Canarias, Spain
J.a. Rodr
í
guez-losada
Departamento Edafología y Geología,Universidad de La Laguna (ULL)
Avenida Astrofísico Francisco Sánchez, La Laguna, Tenerife, Spain
aBsTRacT: The main feature of aquifers in volcanic islands with high rainfall rates and steep
topography is that they are on raised, mainly due to the presence of volcanic dikes. Dikes are igneous
bodies with very high aspect ratio, which means that their thickness is usually much smaller than the other
two dimensions and tend to be vertical or of high dip angle. it can be considered as impermeable and
interconnected walls where aquifers, which are recharged by rain, raise the water table between the dikes.
This is especially important in volcanic rift zones. The method to obtain water in these volcanic areas
involves digging horizontal galleries with explosives. The galleries cross the dikes and drain the water from
the water saturated area. The main problem of this type of perforation is to obtain the water continually,
without the possibility of water regulation. This question has been solved by means of the reconstruc-
tion of several technically viable dikes, to enable the store of water resources through channels in order to
regulate the water wealth of the built galleries. Methods, results and viability on the use of the volcanic
materials as relevant works of civil engineering highlights on the following paper.
1
inTRoDUcTion
subsequently determines the utilization of water
resources through horizontal galleries.
in the oceanic islands, dikes usually appear
grouped in the form of swarms of subparallel
dikes intruding along structural axes known as rift
zones (Walker 1992). in the canary archipelago
rift zones were defined in different islands as struc-
tures playing a key role in processes such as mass
wasting and destruction of ancient oceanic volca-
noes or in the structural control on the growth of
large oceanic-island volcanoes (carracedo 1994,
Rodriguez-losada
et al
., 2000).
1.1
Volcanic areas
The geology around the canary islands is domi-
nated almost entirely by a succession of volcanic
materials and structures. sequences of lava emis-
sions and pyroclastic deposits of highly variable
composition, that present extreme contrasts from
the standpoint of lithology, environment, land-
scape and weather.
1.2
Volcanic dikes and hydrology
Dikes are as nearly vertical walls or thin layers
formed from a dense and compact rock, with lit-
tle width in most cases (1 to 6 m), which play the
role of impervious or semi-permeable screens.
The numerous dikes intact, more or less parallel,
hampering movement and the presence of trans-
verse open cracks, that favor the longitudinal flow
axis, give particular hydrogeological behavior. in
addition, dikes raised the island aquifer, which
1.3
Groundwater resources in volcanic areas
in volcanic island systems, we can establish
two types of aquifers, the first watershed aqui-
fer which is set approximately at elevation 400
to near the higher elevations of the islands and
ridges, this aquifer is tapped through mainly hor-
izontal galleries, although there are some cases
where the aquifer is tapped by drilling wells or
high altitude.
