NOTICE CONCERNING COPYRIGHT
RESTRICTIONS
This document may contain copyrighted materials. These materials have
been made available for use in research, teaching, and private study, but
may not be used for any commercial purpose. Users may not otherwise
copy, reproduce, retransmit, distribute, publish, commercially exploit or
otherwise transfer any material.
The copyright law of the United States (Title 17, United States Code)
governs the making of photocopies or other reproductions of copyrighted
material.
Under certain conditions specified in the law, libraries and archives are
authorized to furnish a photocopy or other reproduction. One of these
specific conditions is that the photocopy or reproduction is not to be "used
for any purpose other than private study, scholarship, or research." If a
user makes a request for, or later uses, a photocopy or reproduction for
purposes in excess of "fair use," that user may be liable for copyright
infringement.
This institution reserves the right to refuse to accept a copying order if, in
its judgment, fulfillment of the order would involve violation of copyright
law.
Geothermal Resources Council TRANSACTIONS, Vol. 17, October 1993
THE DYNAMIC BEHAVIOR OF KILAUEA VOLCANO AND ITS RELATION TO
HYDROTHERMAL SYSTEMS AND GEOTHERMAL ENERGY
Jim Kauahikaua and R.B.Moore
U.S.Geological Survey, Hawaiian Volcano Observatory, Hawaii National Park, HI
U. S . Geological Survey, Denver, CO
ABSTRACT
THE EFFECTS OF VOLCANIC ACTIVITY ON
KILAUEA'S HYDROTHERMAL SYSTEMS
Exploitation of hydrothermal systems on active basaltic
volcanoes poses some unique questions about the role of
volcanism and hydrothermal system evolution. Volcanic
activity creates and maintains hydrothermal systems while
earthquakes create permeable fractures that, at least
temporarily, enhance circulation. Magma and water,
possibly hydrothermal water, can interact violently to
produce explosive eruptions. Finally, we speculate on
whether volcanic behavior can be affected by high rates of
heat extraction.
A hydrothermal system results when a heat source interacts
with groundwater. In most high-temperature hydrothermal
systems exploited for electricity production, the heat source
is a cooling intrusion at some depth beneath the earth's
surface. Kilauea hydrothermal systems are similar in that
they are partially driven by past intrusions but they may
also be intersected and profoundly affected by new
intrusions. Moore and Trusdell (1993), Kauahikaua (1993).
and Ingebritsen and Scholl(l993) have summarized the
evidence for the current location of magma storage areas
and conduits, cooling intrusions, and the resulting
hydrothermal systems.
INTRODUCTION
Most high-temperature geothermal fields around the world
are being mined of stored heat while Kilauea and Iceland
are being mined of a combination of stored heat and heat
supplied in the form of magma from the upper mantle.
Therefore, some unique interactions are possible and this
paper describes what is currently known about the
relationship of the hydrothermal systems of Kilauea to the
dynamic behavior of the volcano, as manifested by the
movement of magma, rock, and groundwater. Much will be
inferred by analogy with Iceland because the record of
exploitation for geothermal energy in Iceland is much
longer than in Hawai'i and because Iceland has many
volcanological similarities to Hawai'i. The material
presented in this paper was first extracted from the
literature to answer questions about these interactions
posed to us by government agencies and groups. The
discussions are meant to explore what is known about each
interaction and the discussions are not necessarily related
to each other.
The interaction of a newly-emp!aced intrusion and an
existing hydrothermal system has been most thoroughly
documented in Iceland. Physical measurements at Krafla
geothermal field confirm that significant pressure,
temperature, and chemical changes can occur. For example,
Elsworth and Voight (1992) describe nearly-instantaneous
transient pressure increases of 0.76 MPa and 0.34 MPa at
distances of 4.3 km and 9.3 km, respectively, from the
1977 and 1978 intrusions. A decrease in pH, a delayed
increase in CO, content in steam, and a rapid increase in
water table elevation was observed in three wells 4.3 km
from and in response to magmatic activity in 1975 and
1977 (Stefansson, 1981). Although pressure and
temperature changes have not been directly observed on
Kilauea in response to volcanic activity, they have been
indirectly observed in the form of self-potential(SP)
changes at the ground surface (Zablocki, 1975). An SP
increase coincident with a fissure eruption in 1973 was
interpreted as the effect of enhanced groundwater
convection produced by a dike being intruded up through
the water table. Additionally, Tilling and Jones (1990)
observed a chemical change in waters tapped by a deep
drill hole at the summit of Kilauea after a southwest rift
zone eruption in 1974 about 1.5 km from the hole.
Geophysical studies have documented that magma moves
upward into the summit area of Kilauea and then moves
laterally into the rift zones. High levels of seismicity
indicate that rock is being fractured and probably displaced
during faulting. Groundwater generally floats as a lens of
freshwater on seawater and moves seaward at ambient
temperature; when heated, groundwater can move upward
as long as there is sufficient permeability. The
hydrothermal systems affect and in turn are influenced by
these three dynamic processes.
The brine chemistry for well HGP-A in Kilauea's east rift
zone showed little, if any, response to the 1983 beginning
of the middle east rift zone (MERZ) eruption 24 km uprift.
HGP-Awas continuously exploited for electricity
129
Kaua h i kaua and Moore
production from 1981 to 1989. During the 8 years of
production, chlorides increased by a factor of ten, the
Na/CI ratio stayed virtually identical to that in seawater,
the WCI ratio decreased steadily, and the Ca/Cl ratios
increased fairly smoothly with time in response to
production (Thomas, 1987). In January 1983, an eruption
began in the east rift zone which, as of this writing (May
1993). is continuing (Heliker and Wright, 1991). With the
possible exception of the MgKl ratio, none of these
chemical measures showed a response related to the start
of the eruption.
the ground surface. Thus, the 1924 explosive eruption
occurred when the bottom of Halema'uma'u pit crater was
only about 100 m above the current level of the water
table. Earlier drops in the level of the lava lake were no
more than 250 m below the ground surface and did not
result in phreatic explosions. By analogy, earlier explosive
eruptions may have occurred at Kilauea summit when the
caldera floor was much lower, and therefore closer to the
water table, than it is now. Macdonald (1962) and other
authors point out that, on the basis of observations of the
1955 and 1960 eruptions, large volumes of steam appear
only when molten lava was temporarily withdrawn from
the surficial part of the vent. The 1924 explosive eruption
occurred when lava was withdrawn from a lava lake.
Therefore, the withdrawing lava column coupled with a
relatively shallow water table probably allows groundwater
to enter the conduit previously occupied by magma and
explosively convert to steam. The degree of explosivity is
related to the amount of water converted to steam in a
given volume.
At Kilauea, the interaction of magma and groundwater has
resulted in catastrophic explosive eruptions, such as those
that produced the ash and tuff deposits at Kilauea summit,
Pu'ulena, and Kapoho described by Moore and Trusdell
(1993), Decker and Christiansen (1984), and McPhie et al.
(1990). At least one of the summit events may have
involved the hydrothermal system (L.G. Mastin, 1993, oral
communication). The timing of these particular events is
fairly well known to have been 200 year before present
(summit), 200-340 years before present (Kapoho), and 400750 years before present (Pu'ulena). There is evidence of
eight other explosive eruptions within the last 100,000
years exposed in the Hilina fault system on the south flank
of Kilauea (Easton, 1987). In addition, there are several
thin ash beds in the cores of the Scientific 'Observation
Holes (SOH, thirteen in SOH-1; Novak and Evans, 1991)
that suggest explosive activity. We must conclude that
these eruptions are infrequent, but not uncommon, in
Kilauea's geologic history. Although the LERZ has been
eruptively quiet since 1961, eruptions will occur there in
the future and magma could intersect the hydrothermal
system near HGP-A, as it did in 1955 (Macdonald and
Eaton, 1964), or basal groundwater or seawater near
Kapoho, as it did in 1960 (Richter et al., 1970). This
recent activity resulted in relatively minor steam
explosions, but larger events could occur. At the summit of
Kilauea, relatively small (compared to 1790) phreatic
explosions occurred in 1924 as the summit subsided in
response to an apparent intrusion at Kapoho on the LERZ
or a submarine eruption east of Cape Kumukahi (Fig.1 in
Moore and Trusdell, 1993; Stearns and Macdonald, 1946;
Decker and Christiansen, 1984). Future caldera-forming
collapses could result in much larger phreatic or
phreatomagmatic explosions, and Holcomb ( 1987) points
out that the current cycle of ERZ activity resembles the
eruptive sequence prior to the 1790 summit collapse and
catastrophic eruptions.
The likelihood of phreatomagmatic activity may also be
increased at specific sites. The locations of steam
explosions during the 1955 and 1960 eruptions were close
to sites of pastyhreatomagmatic activity. Steam was
produced during the initial stages of the 1955 eruption in
the immediate vicinity of Pu'u Honua'ula (Macdonald and
Eaton, 1964) located 1.5 km from Pu'ulena pit crater,
probable source of the Pu'ulena tuff (Moore, 1992).
Although subsequent lava issued from vents as much as 6
km downrift and 10 km uprift from Pu'u Honua'ula, only
the 1955 vent at Pu'u Honua'ula produced steam. Steam
was also produced during the 1960 eruption from a vent
that was 1.5 km from the Kapoho tuff cone. Pu'ulena and
Kapoho crater may be loci of eruptive activity where the
water table is relatively shallow.
THE EFFECT OF FAULTING AND SEISMICITY ON
KILAUEA'S HYDROTHERMAL SYSTEMS
Permeability below about 1 km depth at Kilauea exists
predominantly as fractures. Bulk permeability decreases by
about 4 orders of magnitude between the surface and a
depth of 1,100 to 1,400 m below sea level (Ingebritsen and
Scholl, 1993). Many faults have been mapped within the
rift zones and summit areas of Kilauea and it is likely that
subsurface fault planes provide locally enhanced
permeability. HGP-A had two production layers at 1311 m
and at 1966 m (Chen and others, 1979) which may have
been intersected fractures. More recently, wells KS-7 and
KS-8 intersected a high temperature, fractured zone at 488
m and 1059 m, respectively (Thomas and others, 1991).
The latter fracture zone yielded pressures 47 bars in excess
of hydrostatic pressure which must be confined by
anomalously low permeabilities at these shallow depths
(Ingebritsen and Scholl, 1993). In fact, the discovery of an
overpressured fracture zone at shallow depth in the vicinity
of the Pu'ulena tuff and the 1955 steam eruption (KS-8is
less than 1.5 km from Pu'ulena crater and less than 100 m
The likelihood of steam production and an explosive
eruption may be increased by the availability of shallow
groundwater (Macdonald, 1962). The 1955 and 1960
eruptions occurred where the water table i s approximately
215 m and 25 m deep, respectively. The water table
beneath the summit currently stands at a depth of about
500 m. Dvorak (1992) notes that the 1924 phreatic
eruption at Halema'uma'u pit crater at the summit occurred
when the lava lake level subsided more than 400 m below
130
Kauahi kaua and Moore
and Saemundsson, 1974). Differences include the total
length of the eruptive features (350 km for Iceland and 80
km for subaerial Kilauea) and width of active surface
features (3-10 km for Iceland and 3-4 km for Kilauea).
Iceland is located on a crustal rift which is spreading at a
rate of about 2 cm/y and Kilauea is located over a mantle
hot spot over which the Pacific plate is moving at a rate of
about 9 cm/y (Clague and Dalrymple, 1987).
from the initial 1955 fissure) suggests the possibility that
the two phenomena are related. The phreatic or
phreatomagmatic eruptions may have been the result of
breaching one or more such fracture zones.
There is no direct evidence that earthquakes have affected
the hydrothermal systems of Kilauea. Microseismicity
levels of up to 0.05 events/(km3 yr) and maximum
magnitude M3.0 immediately around HGP-A (Kauahikaua,
1993) and an M6.1 in 1989 about 15 km away had no
documented effect on the performance of the well (D.M.
Thomas, 1992, oral communication) during eight years of
electricity production. Tilling and Jones (1990) did not
note any obvious changes in the NSF research well within
Kilauea caldera in response to the 1975 M7.2 earthquake
whose epicenter was about 25 km away nor to the
simultaneous eruption 2.5 km away within Kilauea caldera.
The effect of high background seismicity in the summit
and rift zones of Kilauea on groundwater or hydrothermal
systems is difficult to evaluate because it is, by definition,
relatively constant, This slim record of observations cannot
be taken as definitive but only indicative that these levels
of seismicity do not significantly alter these specific
hydrothermal systems.
In Iceland, thirty-six years of geothermal development for
production of electricity in the vicinity of active volcanism
have not had any noticeable impact on volcanic activity. In
1990, total electricity production from high-temperature
wells was 45 MWe and total extraction for direct heat
applications was about 480 MWt (Palmason and
Gudmundsson, 1990) for a total extraction rate of about
920 MWt (assuming 10% efficiency in the conversion of
thermal energy into electrical energy). Total average heat
discharge of the Icelandic volcanic zone has been
estimated to be 56 MWt/km to the surface and 78
MWt/km laterally into the crust (Palmason, 1973) for a
total of about 47 GWt integrating along approximately 350
km of rift. In other words, the Icelanders are seeing no
changes in volcanic behavior while they are exploiting
about 2% of the heat being discharged from the volcanic
zone.
THE INTERACTION BETWEEN NONTHERMAL
GROUNDWATER AND KILAUEA’S
HYDROTHERMAL SYSTEMS
A comprehensive heat discharge rate for Kilauea has not
yet been estimated; however, the heat input rate can be
estimated from the magma supply rate. Magma is the
ultimate heat source for Kilauea hydrothermal systems and
adds heat at a rate of 3-7 GWt (Kauahikaua, 1993). There
is, of course, a substantial, unknown amount of heat
already stored within Kilauea in the form of intrusions and
heated water. The rate at which heat is discharged from
Kilauea must be similar in magnitude to the heat input rate
unless the volcano is heating up or cooling off. In fact,
recent findings of alteration minerals existing at the very
high end of their temperature stability fields in cores from
a depth of up to 2 km (Terry Keith, 1993, written
communication) suggest that rocks at these depths may still
be heating up. If correct, the heat discharge rate would be
less than the heat input rate.
There are no known thermal discharges north of either the
east or southwest rift zone where recharge is probably the
highest. Thermal discharges do occur south of the rift
zones where recharge is much lower. In the shallow
groundwater within the rift zone and to the south, the
hottest water is at the water table surface (Epp and
Halunen, 1979) which suggests that it is coming up and
flowing out along the water-table surface to the coast.
The existence of thermal water to the north is better shown
by anomalous chemistry than by enhanced temperatures.
McMurtry et al. (1977) note that slight enrichments of
silica in water from a few wells north of the east rift zone
show that, even with the large amount of recharge in this
area, thermal water has apparently moved from the rift
zone to the north.
Heat extraction rates on Kilauea are currently low but are
planned to be significantly higher. The rate of heat
withdrawn by geothermal well HGP-A was estimated from
an enthalpy of 1650 kJ/kg and a flow rate of 50,000 kg/hr
(ENEL,1990) to be 1650 x 50,000 / (3600 sec/hr) or 22.9
MWt and produced between 2 and 3 MWe. Between 1981
and 1989, HGP-A withdrew heat at less than 1% the rate
of heat supplied to Kilauea. As of this writing (May,
1993), production of electricity from geothermal sources
totals less than 30 MWe (Puna Geothermal Venture, 1993,
written communication) which can be produced by
extracting roughly 300 MWt (assuming similar MWt to
MWe efficiencies as for HGP-A). The State of Hawaii has
proposed geothermal developments providing 500 MWe
POTENTIAL EFFECTS OF GEOTHERMAL
DEVELOPMENT ON VOLCANIC ACTIVITY
The possible range of effects of high rates of heat
withdrawal on a volcano’s dynamic behavior is not known.
Iceland is commonly used as an analogy for Kilauea
because it has certain volcanological similarities to
Kilauea. Both erupt tholeiitic basalts, heat flows range
from above 300 mW/mz within the zone of rifting to 80
mW/mz outside it (Kauahikaua, 1993; Palmason, 1973) and
the eruption rates are about 0.036 km3/yr for Kilauea
(King, 1989) and about 0.048 km3/yr for Iceland (Palmason
131
Kauahi kaua and Moore
the proposal of more detailed hypotheses of possible
interactions. In support of such modelling, better estimates
of the magma supply rate, thermal structure, and general
heat budget are needed for Kilauea.
from Kilauea (Kaya, 1991) which will require extracting
heat at a rate of about 5 GWt. A comparison of this rate to
the rate of heat input to Kilauea by magma supply shows
that the State of Hawaii proposal would require extraction
of heat at a rate approximately equal to the estimated rate
of heat input and discharge for Kilauea volcano.
REFERENCES
When commercial heat withdrawal rates are insignificant
relative to an active volcano’s heat input rate, then the heat
withdrawal will almost certainly not affect the future
dynamics of the volcano. When the heat withdrawal rate
approaches that of volcanic heat input, the possibility of
that withdrawal affecting volcano dynamics increases. For
example, Hardee (1987) showed that differences in
eruptive behavior along the east rift zone can be explained
by different thermal regimes due to differing intrusion
rates. In the upper east rift zone, a magma conduit can
remain open because the volume rate of throughput is high
enough to keep the conduit above melt temperature.
Magma can flow through this conduit relatively
aseismically. A lesser volume rate of throughput in the
lower east rift zone is insufficient to keep a magma
conduit open and magma must be forcefully intruded or
erupted. If instead of varying intrusion rates, the thermal
regime is cooled by a locally-intensivewithdrawal of heat,
the effect would still be the same and the ability of magma
to flow laterally through a conduit might be decreased. For
this reason, we suggest that active volcanic regions
undergoing intense geothermal exploitation be carefully
monitored for long-term changes that may indicate such
interactions. Based on Hardee’s results (Hardee, 1987), the
effects of high heat withdrawal might include increased
seismicity and decreased surface volcanic activity locally,
but observable only over a long time period.
Chen, B.H., Kihara, D.H., Seki, A., and Yuen, P.C., 1979,
Well Test analysis of HGP-A: Society of Petroleum
Engineers of AIME Paper SPE 7963, presented at
the 1979 California Regional Meeting, Ventura,
April 18-20.
Clague, D.A., and Dalrymple, G.B.,1987, The HawaiianEmperor volcanic chain, Part I, Geologic evolution,
USGS Professional Paper 1350, p. 5-54.
Decker, R.W., and Christiansen, R.L., 1984, Explosive
eruptions of Kilauea volcano, Hawaii in Explosive
Volcanism: Inception, evolution, and hazards,
Washington, D.C., National Academy Press, p. 122132.
Dvorak, J.J., 1992, Mechanisms of explosive eruptions of
Kilauea volcano, Hawaii, Bull. Volc., v. 54, p. 638645.
Easton, R.M., 1987, Stratigraphy of Kilauea volcano,
USGS Professional Paper 1350, p. 242-260.
ENEL (Ente Nazionale per L’Energia Electrica) (1990) The
Kilauea East Rift Zone, Draft report to State of
Hawaii, Dept. Business and Economic
Development, 99 p.
SUGGESTIONS FOR FUTURE RESEARCH
Elsworth, D., and Voight, B., 1992, Theory of dike
intrusion in a saturated porous solid, JGR, v. 97, p.
9105-9117.
Exploration and exploitation of Kilauea’s hydrothermal
systems are at a very early stage. Eruptions will continue
along the east rift zone and they will probably affect any
network of production wells located there in some way;
experience in Iceland suggests that the effects will be
minimal unless the eruption occurs within 10 km of the
production wells. Much work still needs to be done on the
interactions between volcanism, groundwater, and
hydrothermal activity. Participation by the hydrothermal
systems in phreatic eruptions is suggested for Kilauea
summit and needs more study especially in the lower east
rift zone. Definition of permeabilities at depth is crucial to
the understanding of these hydrothermal systems - our
current rudimentary information is simply not sufficient to
assess potential geothermal reserves in the Kilauea east rift
zone. A network of observation wells would provide
information on the effects of exploitation on the shallow
water table and the deeper hydrothermal systems. Finally,
there is currently no clear way to determine the effects of
development on magmatic activity; further modelling of
magma conduit dynamics and the effects of heat
withdrawal, such as is done in Hardee (1987), would allow
Epp, D. and Halunen, Jr., A.J., 1979, Temperature profiles
in wells on the island of Hawaii, Hawaii Institute of
Geophysics technical report HIG-79-7, 31 p.
Hardee, H.C., 1987, Heat and mass transport in the eastrift-zone magma conduit of Kilauea volcano, USGS
Professional Paper 1350, p. 1471-1486.
Heliker, C.C., and Wright, T.L., 1991, The Pu‘u ‘0‘0Kupaianaha eruption of Kilauea, Eos, v. 72, p. 521,
526, and 530.
Holcomb, R.T., 1987, Eruptive history and long-term
behavior of Kilauea volcano, USGS Professional
Paper 1350, p. 261-350.
Ingebritsen, S.E., and Scholl, M.A., 1993 in press, The
Hydrogeology of Kilauea Volcano, Geothermics, v.
132
Kauahi kaua and Moore
Richter, D.H., Eaton, J.P., Murata, K.J., Ault, W.U., and
Krivoy, H.L., 1970, Chronological narrative of the
1959-1960 eruption of Kilauea volcano, Hawaii,
U.S.G.S. Professional Paper 537-E, 73 p.
22.
Kauahikaua, J., 1993 in press, The geophysical
characteristics of Kilauea’s hydrothermal systems,
Geothermics, v. 22.
Stearns, H.T., and Macdonald, G.A., 1946, Geology and
ground-water resources of the Island of Hawaii,
Hawaii Division of Hydrography Bulletin 9, 363 p.
Kaya, M., 1991, Master planning for the Hawaii
geothermal/deep water cable project, GRC Bull.,
March, p. 67-69.
King, Chi-Yu, 1989, Volume predictability of historical
eruptions at Kilauea and Mauna Loa volcanoes, J.
Volcanol. Geothermal Res., v. 38, p. 281-285.
Stefansson, V., 1981, The Krafla geothermal field,
northeast Iceland in Geothermal Systems: Princides
and Case Histories, Rybach, L., and Muffler, P.,
(eds.), John Wiley and Sons Ltd., p. 273-294.
Macdonald, G.A., and Eaton, J.P., 1964, Hawaiian
volcanoes during 1955: U.S.Geological Survey
Bulletin 1171, 170 p.
Thomas, D. (1987) A geochemical model of the Kilauea .
east rift zone, U.S.Geological Survey Professional
Paper 1350, pp. 1507- 1525.
Macdonald, G.A., 1962, The 1959 and 1960 eruptions of
Kilauea volcano, Hawaii, and the construction of
walls to restrict the spread of the lava flows:
Bulletin Volcanologique, v. 24, p. 249-294.
Thomas, R., Whiting, R., Moore, J., and Milner, D. (1991)
Independent technical investigation of the Puna
Geothermal Venture Unplanned Steam Release,
June 12 and 13, 1991, Puna, Hawaii, report
prepared for the mayor of Hawaii County and the
Chairperson of the State of Hawaii Board of Land
and Natural Resources, 38 p.
McMurtry, G.M., Fan, P.-F., and Coplen, T. B., 1977,
Chemical and isotopic investigations of groundwater
in potential geothermal areas in Hawaii: Am. J.
Sci., v. 277, p. 438-458.
Tilling, R.I., and Jones, B.F. (1990) Temporal Variations in
composition of water above the magma reservoir of
Kilauea volcano, Hawaii, Eos, 71, p. 663.
McPhie, J., Walker, G.P.L., and Christiansen, R.L., 1990,
Phreatomagmatic and phreatic fall and surge
deposits from explosions at Kilauea volcano,
Hawaii, 1790 A.D.: Keanakakoi Ash Member, Bull.
Volc., V. 52, p. 334-354.
Zablocki, C.J. (1975) Mapping thermal anomalies on an
active volcano by the self-potential method,
Kilauea, Hawaii, U.N. symposium on the
development and use of Geothermal Resources 2,
1299-1309.
Moore, R.B., 1992, Volcanic geology and eruption
frequency, lower east rift zone of Kilauea volcano,
Hawaii, Bull. Volc., v. 54, p. 475-483.
Moore, R.B., and Trusdell, F.A., 1993 in press, Geology of
Kilauea Volcano, Geothermics, v. 22.
Novak, E.A., and Evans, S.R. (1991) Preliminary.results
from two Scientific Observation Holes on the
Kilauea East Rift Zone, GRC Trans. 15, 187-192.
Olson, H.J., and Deymonaz, J.E., 1992, The Hawaiian
scientific observation hole (SOH) program summary
of activities, GRC Trans., v. 16, p. 47-53.
Palmason, G., 1973, Kinematics and heat flow in a
volcanic rift zone, with application to Iceland,
Geophys. J. R. Astr. SOC.,v. 33, p. 451-481. Palmason, G., and Gudmundsson, A., 1990, Iceland
Country Update, Trans. GRC, v. 14, p. 11 1-126.
Palmason, G.,and Saemundsson, K., 1974, Iceland in
relation to the Mid-Atlantic Ridge, Annual Review
of Earth and Planetary Sciences, v. 2, p. 25-50.
133