Environmental Engineering Reference
In-Depth Information
The thickness of the single lava flows decreases
from the intermediate (1-1.5 m thick) to the upper
and top lava members (up to 0.5 m thick). in the
intermediate and upper lava members some inter-
bedded scoriaceous layers are present. The upper
and top lava members are characterized by several
cavities made of a thin crust. When an artificial
filling, covering the external roof of the cave was
removed, a volcanic landscape made of highly
vesicular, cavernous-type lava flows appeared,
referred to as shelly pahoehoe lavas. shelly pro-
duces cavernous flows with fragile crusts. other
surface features (hornitos, pressure ridges, tumuli
and others) that usually occur on pahoehoe lavas
are not present here and may have been destroyed
during the construction of the Tourist centre.
Discontinuities among and inside the different
basaltic units are a common feature. as the dif-
ferent basaltic flows cool, shrinkage occurs and
cracks form in the rock. sometimes these disconti-
nuities are responsible for unstable blocks of rock
up to 1m across on the sides and the roof of the
cave. Domed sections of the roof testify that col-
lapses occurred in the past at the joint intersection
of fractured rock. in any case it appears that the
sides and roof of the cave have evolved in order to
achieve more stable rock profiles.
The lTU is spatially limited to the backstage/
upstage, the stage and the first 8 rows of seating.
only in the zone of the backstage does the lava
tube structure appear to be in its original state
showing thin layers of lava with a concentric shell
structure (like an onion) and levees (terraces mark-
ing different stages of filling flows). The shell was
formed where the lava chilled against the colder
rock. Most of the roof appears to be a circular
stable arch. The tube profile here is in the shape of
an “eight” (two superimposed circles). This profile
is the result of the cooling of lava flow surfacing to
produce a crust, beginning at the levees and grow-
ing inward and downstream.
an active lava flow is actually a river of lava, a
central stream of molten rock with levees of solid
lava along its sides. as the lava continues to flow,
the two sides start to form a roof across the flowing
lava. When the two sides have completely covered
the flowing lava, a lava tube is formed. sometimes
the flow sides form levees as the sides harden,
and the top remain liquid. at the stage and in
particular in the auditorium (first 8 rows of seat-
ing) the lTU is spatially limited to the central part
of the roof. here the lTU presents features like
adaptation folds, a fissure where the levees came
together and glaze structures.
Most of the roof associated with the simultane-
ous presence of lTU and MlU appears to be a
broad and stable arch.
3
PRoBleMs DeTecTeD
in The aUDiToRiUM
3.1
Approach adopted
The problems detected in the area of study had a
variety of pathologies of very different levels of
magnitude which had to coexist:
- from the possible structural instability of com-
plete packets of rock,
- to the possible “chineo”, (detaching of parti-
cles the size of sand or less), in areas which have
deteriorated.
