Environmental Engineering Reference
In-Depth Information
Geotechnical characterization of volcanic rocks and soils
of Madeira island
J.c. lourenço, J.M. Brito, J. santos, s.P.P. Rosa, V.c. Rodrigues & R. oliva
Cenorgeo, Geotechnical Engineering, Lisbon, Portugal
aBsTRacT: This paper focuses on the description and the characterisation of volcanic rocks and soils
of Madeira island, based on data from expertise judgment, field survey and laboratory tests. The objec-
tive has been the compilation of data from geotechnical designs for Madeira island, in the last 20 years,
in order to describe the geological conditions and to evaluate the geotechnical parameters of the main
volcanic formations such as: basalts, breccias and tuffs.
1
sTRUcTURe anD GeoloGY
oF MaDeiRa islanD
1.1
Introduction
The archipelago of Madeira is composed by a
group of four islands located on the atlantic ocean:
Madeira, Porto santo, Desertas and selvagens
(
Fig. 1
).
The Madeira island's shape is elongated with a
maximum length of about 57 km (W-e), between
Ponta do Pargo and são lourenço, and a width of
about 23 km (n-s), between Ponta de são Jorge
730 km
2
which corresponds to 90% of the total
area of the archipelago. it has an average altitude
of 700 m being the maximum equal to 1819 m.
The island was originated from submarine vol-
canic eruptions, mostly explosive, during the Vin-
bondonian period (Zbyszewsky quoted by Rosa,
1995). This initial phase was followed by others
more effusive with prolific emission of basaltic
lavas.
Figure 2. simplified plan of the volcanic complexes
(proposed by Zbyszewsky
et al
., quoted by Rosa, 1995).
1.2
Volcanic complexes
1.2.1
Introduction
Madeira island comprises five volcanic complexes
as shown in Figure 2. The division between com-
plexes is questionable because it is mainly based
on morphological and geometrical criteria being
presented in this paper the division proposed by
Zbyszewsky
et al
(quoted by Rosa, 1995). The
main complexes are β
1
and β
2
.
1.2.2
Ancient volcanic complex
(
β
1
)
This complex, dated from the Mio-Pliocenic period,
occurs mainly in the central part of the island
namely in curral das Freiras, serra de Água, Vale
de s. Vicente, Vale da Boaventura, Ruivo and aree-
iro mountains, são Roque, Porto da cruz, Machico
and Ponta de são lourenço. it is believed that this
complex is older than 5.2 Ma due to the existence
of some calcareous fossils dated from this period.
it consists mainly of diversified pyroclastic
material with some intercalations of basaltic lava
flows mostly very weathered.
Figure 1.
Geographical location of Madeira archipelago.
