Environmental Engineering Reference
In-Depth Information
Table 9.
comparative analysis of the deformations produced by lava fields in different volcanoes.
lava field parameters
Deformation
Detection
(km) from
area with
maximum
thickness
µrad/a at
1 km from
the axis
Thickness
(m)
a
(km 2 )
V
(km 3 )
Volcano
Year
mm/year
source
sakurajima
(Japan)
1946
50
0.18
14
14
1.7
(24)
Pitón de la
Fournaise
1976
20
(18)
(1986-89)
1976
5
(1986-89)
1986
10
(1986-89)
arenal
(costa Rica)
1968-present 150 (compound
thickness)
7.5
0.75
30-60
60
5
(5)
(1968-2003)
etna (italy)
1981, 1983
75
(35)
1986-1987
15
6.5
0.06
22
(14)
1989
10 (compound 40)
3.3
0.0033
47
Table 10.
settlements determined under different methods and media (in meters).
Geological media of load
Type and thickness
lava (20 m)
lava field (150 m)
cone (900-1100 m)
Period
Days-Months
35 years
7000 years
1
initial settlements
0.001-0.04
0.11-4.1 (1.3-2)
0.44-16 (5.2-8)
2
immediate-primary settlements using cc
0.48-0.53
7.8-15.0
20.0-29.7
3
elastic methods through finite element analysis
-
-
4.98-7.16
4
elasto-plastic methods through finite element
analysis
-
0.72
4.95-7
5
Total settlements (1 + 2)
0.48-0.57
7.9-19.1
20.4-45.0
6
settlements based on inclinometers
(∼18% of consolidation)
-
∼2
-
the volume is at least the times (0.6 km 3 against
0.18 km 3 ), as well as its thickness than the one at
the lava profile of the sakurijama Volcano. it also
has twice its thickness than the profiles of the etna
flows (around 75 m).
When we compare the deflation rates associated
to the sakurajima and etna flows with the ones
from the arenal Volcano, we find that they are very
similar. considering the differences in the covered
area, thickness and volume, 1 km away from the
axes, we have 40 µrad/year at the etna, 14 at the
sakurajima, and 60 and 30 at the B and c stations
at the arenal Volcano (total weight is 1012 kg),
seems like a plausible and concrete explanation,
according to the field observations and data from
the inclinometers (2, 4, 33, 42, 53).
Theoretically, we can pass from angular meas-
urements to settlements at the maximum thick-
ness axial axis. in 41 years (1968-2009), we can
argue that close to the maximum lava thickness
and when a µrad has a value of a millimeter in the
vertical direction (when d = 1 km), we have a slow
deformation from 40-64 mm/year, that by extrapo-
lation would be 1.41 m (according to soto, 1991)
and 2.03-2.24 m (5) of subsidence. a value of 2 m
seems likely, since it counts with a larger amount
of data.
6
conclUsions
- since the arenal volcano is made predominantly
of a lava cone that grew up on a volcanic base-
ment composed mostly of fractured (incom-
petent mechanical level), an overweight would
generate the necessary geotechnical conditions
for: 1) deform its foundation (subsidence, folding
or failure due to an overload) and, 2) unsettling
the cone.
 
Search WWH ::




Custom Search