HYDROGEN AND OXYGEN ISOTOPIC COMPOSITIONS OF WATERS FROM FUMAROLES AT KILAUEA SUMMIT, HAWAII

Todd K. Hinkley
  Mail Stop 903
  U.S. Geological Survey
  Box 25046 Denver Federal Center
  Denver, CO 80225

  Tel: (303) 236-5858
  FAX: (303) 236-1414
  email: thinkley@greenwood.cr.usgs.gov

James E. Quick
  U.S. Geological Survey
  MS 903
  Box 25046 Denver Federal Center
  Denver, CO 80225

Robert T. Gregory
  Department of Geological Sciences
  Southern Methodist University
  Dallas TX 75275

Terrence M. Gerlach
  Cascades Volcano Observatory
  U.S. Geological Survey
  5400 MacArthur Blvd.
  Vancouver WA 98661

Abstract

Condensate samples were collected in 1992 from a high-temperature (300)
fumarole on the floor of the Halemaumau Pit Crater at Kilauea. The
emergence about two years earlier of such a hot fumarole was basically
unprecedented at such a central location at Kilauea.  The condensates have
hydrogen and oxygen isotopic compositions that indicate that the waters
emitted by the fumarole are composed largely of meteoric water, that any
magmatic water component must be minor, and that the precipitation that
was the original source to the fumarole fell on a recharge area on the
slopes of Mauna Loa Volcano to the west.  However, the fumarole has no
tritium, indicating that it taps a source of water that has been isolated
from atmospheric water for at least 40 years.  It is noteworthy,
considering the unstable tectonic environment and abundant local rainfall
of the Kilauea and Mauna Loa regions, that waters that are sources to the
hot fumarole remain uncontaminated from atmospheric sources over such long
times, and long transport distances.

As for the common, boiling point fumaroles of the Kilauea summit region,
their 18O, D, and tritium concentrations indicate that they are dominated
by recycling of present day meteoric water.  Though the waters of both hot
and boiling point fumaroles have dominantly meteoric sources, they seem to
be of separate hydrologic regimes.

Large concentrations of halogens and sulfur species in the condensates,
together with location at the center of the Kilauea summit region and high
temperature, initially suggested that much of the total mass of the
emissions of the hot fumarole, including the H2O, might have come directly
from a magma body.  The results of the present study indicate that it is
unreliable to infer a magmatic origin of volcanic waters based solely on
halogen or sulfur contents, or other aspects of chemical composition of
total condensates.

INTRODUCTION

Little is known about the hydrothermal systematics of Kilauea Volcano, or
of volcanic edifices in general.  Field and chemical studies of water and
other emitted volatiles have been conducted since the nineteenth century
(see Shepherd, 1938).  Geophysical studies and drilling have located bodies
of groundwater in the Kilauea region (Keller et al., 1979; Jackson and
Kauahikaua, 1988).  Most fumaroles on Hawaii are low temperature (<100C,
Casadevall and Hazlett, 1983), called "boiling point" fumaroles because
they are maintained at their boiling temperatures for their respective
elevations, by the latent heat release from liquid condensation.  They
have generally been interpreted as emitting meteoric water that has been
cycled through shallow hydrothermal convection systems.  Hot fumaroles,
with temperatures of about 300C, were recently described (Gerlach et al.,
1991) within Halemaumau Pit Crater, within the Kilauea summit region
(Fig. 1).  Because of the unprecedented combination of their high
temperature and their location at the possible epicenter of the Kilauea
magmatic system, we wished to collect samples from them for information
about the hydrothermal systematics of this much-studied volcano.  We
analyzed the samples for isotopes of oxygen and hydrogen to give
information about possible sources of the waters emitted by the
fumaroles.  Tritium was of particular interest, because of its short half-
life, for detecting the presence of young meteoric waters.  Our results
demonstrate that, contrary to preliminary indications from fumarole
chemical composition that emissions could have a magmatic source, all of
the fumaroles were dominated by meteoric water.

SITE, SAMPLE COLLECTION, AND COLLECTION SYSTEMATICS

Sample sites of the present study are shown in Fig. 1.  Two hot fumaroles,
W-2 and W-3, were on the south end of the floor of the Halemaumau Pit
Crater, and vented with temperatures of ~300C in 1991 and 1992.  We also
sampled two boiling point fumaroles, one known as HMM located near the rim
of the Halemaumau Pit Crater, the other known as Sulphur Bank, ~4km away
near the rim of the Kilauea caldera.  The main suite of condensates was
collected in latest March and earliest April 1992, after several months of
lower-than-average rainfall.

We used a sampling apparatus consisting of three serial traps that allows
collection of the large volumes (~1 l) necessary for high-precision
tritium analysis.  Details of sampling are given in the caption of Fig.
2.  Tritium data are presented in Table 1 for first collection traps only,
because the volumes of condensates collected in subsequent traps were too
small to analyze (Ostlund and Dorsey, 1975).  A preliminary 1991
collection used a simpler apparatus, and was made following a period of
normal rainfall.

All of the isotopic data from the traps indicate that stable isotopes are
fractionated by the sampling apparatus.  Large differences between
isotopic compositions of successive traps in the collection apparatus
suggest that no single trap of our apparatus gives the true composition of
the waters actually emitted by a fumarole.  Contrasting D and 18O values
between first and second traps were 40 and >4 per mil, respectively.  The
compositions of the condensates in the first traps provide upper limits on
the D and 18O concentrations of the waters emitted by the fumaroles,
because condensed water is isotopically heavier than the vapor from which
it condenses, in the pressure and temperature ranges of our experiments.

However, the original isotopic composition of fumarole water actually
emitted by the fumarole can be inferred more precisely, by three different
methods that can be used for correcting or restoring theD and 18O values
of the condensates to the probable actual compositions of waters
originally emitted by the fumaroles.  The three methods are used to plot,
in Figures 3 and 4, these D and 18O compositions of the original
emissions.  In the Figures the resulting data points are shown by separate
symbols for each method.  The methods use the isotopic compositions and
masses of the samples in the serial collection traps, and are as follows.

First, if it is assumed that insignificant water is lost from the
condensation line, the mass-weighted average of the isotopic compositions
of the condensates in the separate traps is the original isotopic
composition of the vapor from the fumarole.  Second, condensation may be
modelled as a batch process.  The batch model is described by two
simultaneous equations:

where n refers to the vapor leaving the first measured trap and n+1 refers
to the next trap downstream.  The fraction of vapor, f, refers to the
vapor exiting the trap after condensation and equilibration in the
trapping volume.  The quantity (1-f) is the fractional amount of liquid
condensed in the trap.  The quantity a is the liquid-vapor isotopic
fractionation factor for 18O.  Analogous equations may be written for
hydrogen, with a different fractionation factor.  As a third alternative,
the initial composition of the vapor may be modelled assuming Rayleigh
condensation in the traps.  The stable isotopic compositions of water (l)
condensed from vapor during Rayleigh fractionation are given by:

dl = a[dvo + 1000]fa-1 -1000

with one equation for each isotope, 18O and D.  vo is the initial isotopic
composition of the vapor.  The average stable isotopic compositions, <l>,
for 18O and D of liquids condensed in collection trap number t can be
calculated by integrating the above equations, with the result:

<dl >  =  {[dvo + 1000][ft-ft-1a] - 1000}/[ft-ft-1]

where ft-1 and ft are the fractions of initial water in the vapor entering
and leaving the trap, respectively.  In the special case of the first
trap, ft-1 = fo = 1.  Because more than one trap was collected, a series
of parallel equations may be constructed and solved for 18Ovo and D.  For
the Rayleigh calculation, a values were specified based on the temperature
dependencies described by Bottinga and Craig, 1969, and Majoube, 1971
respectively.  We assumed temperatures in the first traps of 97C, the
boiling temperature at the altitude of collection, and in subsequent traps
of 23C, the ambient temperature.

All three models predict compositions closer to those of the first traps,
consistent with the largest volumes being retained in the first traps.
The compositions specified by the batch and Rayleigh models are
indistinguishable from one another.  Both are isotopically lighter than
the values specified by the simple mass balance model, because the latter
does not account for the small amounts of isotopically light H2O that did
escape from the collection system.

For boiling point fumarole HMM and hot fumarole W-3, all three correction
procedures predict emitted water compositions that lie on the lines
joining the compositions of the first and second traps (Figure 3).  At
boiling point fumarole Sulphur Bank, the condensate collected in the third
trap was analyzed for D and 18O separately, whereas at W-3 and HMM the
condensates from second and third traps were combined.  At W-3 and HMM the
volumes in first traps were about ten times larger than those in
subsequent traps.  At Sulphur Bank, the volume in the first trap was only
about twice as large as in the subsequent traps, indicating that the
collection process was somehow different there.  Also, compared to the
other two fumaroles, the total amount of water collected per unit time at
Sulphur Bank was greater by about 50%, and larger amounts of condensed
water were visible in the line leading from the fumarole to the first trap.

RESULTS

The volumes of condensates collected in traps are presented in Table 1.
Also in Table 1 are isotopic compositions of condensates in each trap, and
of rain, river water, and ocean water from the island of Hawaii analyzed
as part of the present study.  The stable isotopic data for the fumarole
condensates are presented diagrammatically in Figure 3.  The condensates
from HMM define a linear array that lies to the left of the meteoric water
line (Craig, 1961), and parallel to it.  The hot fumarole W-3, despite
venting at a temperature 200C hotter than HMM, also defines a linear array
that  parallels the meteoric water line, but lying to its right. In
contrast, the data from the boiling point Sulphur Bank fumarole form a
more gently sloping array discordant to the meteoric water line.

The boiling point fumaroles are clearly distinguished from the hot
fumarole by their much higher tritium concentrations (Table 1), ranging
from 0.8 T.U. at Sulphur Bank to 1.5 at HMM.  These values, although
slightly lower than values for rain and ocean water, are consistent with
the presence of young meteoric water (Mazor, 1991; table, chap. 10).  In
contrast, the high temperature fumarole samples have tritium
concentrations that are close to or equal to zero.

DISCUSSION

Although the ranges in isotopic compositions between separate traps for
each of the collections show that there is a large amount of fractionation
during condensation, the actual isotopic compositions of water emitted
from the fumaroles can be closely estimated in three different ways, using
the compositions and masses of the collections in each serial trap from
the condensation, as discussed above.  These three correction methods lead
to restored isotopic composition values that are very close to one
another, although there are slight, systematic differences among them, as
seen by the distinct symbol types shown in Figs. 3 and 4.  The restored
compositions define the isotopic compositions of the waters emitted by the
fumaroles with accuracy and precision adequate for the discussion of the
present study.

The data indicate that none of the isotopic ratios of the fumarole waters
is close to those of magmatic waters.  Estimates for the composition of
magmatic water lie within a relatively small range of oxygen isotopic
compositions,  to the right of the meteoric water line (Sheppard and
Epstein, 1970; Dixon, et al., 1991; Figure 4).  For purposes of this
paper, magmatic water refers to H2O that was dissolved in a silicate magma
independent of its origin (e.g. Sheppard, 1986).  The water dissolved in a
silicate magma can, in principle, come from a variety of sources in the
crust and the mantle.  Because of the effect of plate tectonics on the
recycling of surface fluids into the source regions for basalt, it is
virtually impossible to differentiate juvenile water from magmatic water
on the basis of oxygen and hydrogen isotopes (e.g. Taylor, 1977; Sheppard,
1986).

The most probable sources of magmatic water are from the melting of
hydrous minerals in the source regions of magmas and from the assimilation
of hydrous wall rocks during the ascent through the crust or from
residence in crustal magma chambers where stoping occurs.  There is little
stable isotopic evidence that crustal pore fluids directly diffuse across
plutonic contacts into molten magmas (Taylor and Forester, 1979).
However, assimilation and stoping of hydrothermally altered rocks into
magma chambers can indirectly transfer surface waters into magmas (Taylor,
1977; Michael and Schilling, 1989).

In general, oxygen is a major element in silicate magmas, and magmatic
waters are enriched in 18O relative to the magma, i.e. the silicate oxygen
reservoir buffers the oxygen isotope composition of magmatic water.
Hydrogen is a minor element in silicate magmas.  Therefore, the D value of
magmatic waters may more directly reflect the immediate source of the
fluid or the mixing of hydrogen reservoirs that results from partial
melting and assimilation coupled with fractional crystallization.

From the definition, the stable isotopic composition of magmatic water is
expected to be in isotopic equilibrium with silicate magma.  Because
silicate-water oxygen isotope fractionations (the difference in the 18O
values between magma and water) reverse at magmatic temperatures (change
from positive to negative; e.g. see Javoy, 1977), the oxygen isotope
composition of magmatic water is enriched relative to the magma.  Hence,  +
6 basalts exsolve magmatic waters with  18O values >+6.  In basaltic
systems, these magmatic waters are expected to exsolve at temperatures
approaching 1000C.

Most fumaroles on Hawaii do not approach these temperatures.  If the
fumaroles contain any exsolved magmatic water, the water must lose heat to
the surrounding country rocks.  Because the stable isotope fractionation
between fluid and water is a function of temperature, the exsolved fluid
will exchange stable isotopes with the surrounding rocks during the ascent
to the surface.  In a rock-dominated system, the fluid becomes more
depleted (i.e., takes smaller 18O and D concentrations) the lower the
temperature.  At the temperature of the hot fumaroles (300C, the fluid in
equilibrium with typical Hawaiian basalt still would have 18O>+4 (e.g.
Bowers and Taylor, 1985).  At higher ratios of magmatic fluid to rock, the
fluid would be even more enriched.  The high temperature fumaroles at
Kilauea have 18O values inconsistent with their origin as magmatic waters
isotopically reequilibrated at lower temperature.  The Kilauea hot
fumarolic waters, 18O -4, are far too depleted in 18O to be explained by
this mechanism.

Hydrogen isotopes are more difficult to interpret in magmas because of the
low abundance of hydrogen in the crust and mantle.  In basaltic and
andesitic systems D values range from about -25 to -85 per mil (e.g.
Taylor, 1986).  Because this range of D values overlaps both the range of
surface fluids over a large part of the Earth (see table 1) and the range
of D values of many sedimentary and metamorphic rocks, hydrogen isotopes
are less diagnostic of the sources of fumarolic fluids.

Even though the hydrogen isotopic compositions of the fumaroles are not
diagnostic, the 18O-depleted character of the fumarole waters clearly
implicates meteoric waters.  The term meteoric water refers to any waters
passing through the surface water cycle in the form of atmospheric
precipitation, rain, snow, ice, etc.  These waters are ultimately derived
from the ocean.  Lakes, rivers, and shallow ground water reservoirs are
dominated by meteoric waters.  Modern meteoric waters are remarkably
regular in their stable isotopic composition, exhibiting a linear
relationship between D and 18O values known as the meteoric water line.

The proximity of the data of the present study to the meteoric water line
suggests that the fumaroles are dominated by meteoric water.  The position
of HMM to the left of the water line suggests that there is no significant
involvement of magmatic water in that system.  Although it is possible
that W-3 and Sulphur Bank waters may be mixtures of meteoric and magmatic
water, Figure 4 indicates that no more than about 15 percent of W-3 and 25
percent of Sulphur Bank could be magmatic.  In fact, the stable isotopic
compositions of all of these fumaroles can be adequately explained by
processes that do not involve magmatic waters.

Processes affecting the isotopic compositions of waters of fumaroles are
likely to be complex, and different effects may dominate different
fumaroles.  Fumarolic waters at W-3 and Sulphur Bank may have been shifted
away from the water line to heavier oxygen values by exchange with
basaltic rocks at high temperature (Figure 4; Craig, 1966; Muehlenbachs,
1986).  The composition of HMM may represent a shift away from the
meteoric water line by low-temperature hydration of basaltic glass, which
moves water compositions toward lighter oxygen compositions and slightly
heavier hydrogen compositions (Figure 4; Friedman and Smith, 1958; Frape
and Fritz, 1982).  Alternatively HMM waters may be vapor products of
disequilibrium evaporation.  In any case, all three fumaroles are
dominantly if not completely meteoric water.  This is particularly
important in the case of W-3, which had previously been identified as a
candidate for presence of magmatic water on the basis of its high
temperature, central location, and the presence of halogen and sulfur
species (to 1600 ppm HCl and 400 ppm HF, Gerlach et al., 1992).  Because
of mass and concentration considerations, halogen and sulfur species must
necessarily be identified with sources in magma bodies, whereas water
components of fumarole emissions have multiple and varied potential
sources.

At Sulphur Bank the gentle slope of the data array suggests disequilibrium
condensation (Craig, 1966).  The slope could also be explained by the
presence in the fumarole emissions of a mixture of gaseous and liquid H2O
in isotopic disequilibrium.  Sulphur Bank was the only fumarole where
water droplets were abundant in the line leading from the fumarole to the
first condensation trap.  No point calculated by the Rayleigh model (see
above) for isotopic composition of water emitted by Sulphur Bank is shown
in Fig. 3.  In any case, both batch and mass balance models for
calculating the isotopic composition of water emitted by the fumarole
indicate that the composition of Sulphur Bank is similar to that of W-3.

Tritium concentrations in the fumaroles place important constraints on the
residence time of meteoric waters in the subsurface, because of the short
half-life of that nuclide (Jenks, 1955).  Effectively, all tritium in
meteoric water results from atmospheric thermonuclear testing that began
in the early 1950's (Ostlund and Mason, 1974, 1985), except for a small
amount from decay of cosmogenic 15N, also in the atmosphere (Mazor,
1991).  Condensates from boiling point fumaroles have tritium abundances
in the range of present-day meteoric water (Ostlund and Mason, 1974).  In
marked contrast, waters of the hot fumarole system contain virtually no
tritium (Table 1).  The absence of tritium in waters of the hot fumarole W-
3 indicates that the meteoric component of that fumarole was isolated from
the atmosphere for at least 40 years, the length of time that has passed
since the beginning of atmospheric thermonuclear bomb testing (Doney et
al., 1992).

Regardless of whether the composition of waters of hot fumarole W-3
reflects high-temperature exchange with rock, or mixing with a small
amount of magmatic water, the relationships in Figures 3 and 4 suggest
that the original composition of the meteoric component of that fumarole
was approximately 18O = -6 and D = -40. This isotopic composition is
bracketed by the compositions of precipitation on the island of Hawaii
(Fig. 4 of present paper; also see Scholl et al., 1993).  More
specifically, it is bracketed by the extremes of the precipitation that
falls over a range of elevations on a recharge area on the flanks of Mauna
Loa (Fig. 3).  The isotopic composition of water in aquifers typically
represents that of the local precipitation contributing to groundwater
recharge (Joseph et al., 1992; Fontes et al., 1969; Arnason, 1977).
Permeability data for Kilauea Summit (Keller et al., 1979) indicate that
decades would be required for water to reach the fumaroles at Kilauea from
that area, consistent with the requirement from the tritium data that
meteoric water be isolated for more than 40 years.

The Kilauea region in general is subject to continual volcanic intrusion
and eruption and accompanying tectonic dynamic processes, and is an area
of high average rainfall.  More specifically, the Halemaumau Pit Crater is
certainly subject to the same processes.  Large fluxes of rainwater
cascade over its rim onto its floor during intense rains.  It is an
accumulation point for a substantial surrounding drainage area.  It is
noteworthy in light of both tectonic and rainfall considerations that the
hot fumarole waters appear uncontaminated by young, tritium-bearing
meteoric waters.  At a minimum, our results extend the findings of
Kroopnik et al. (1978) who reported the presence of low-tritium bodies of
groundwater in the more tectonically and thermally stable Puna region of
Hawaii.

If only from relatively high emission temperature, it is clear that the
hot fumarole waters have been in contact with rock of substantially high
temperatures.  At Kilauea and other sites, long-period earthquakes,
commonly preceding phreatic eruptions, may be associated with presence of
waters in deep, hot zones of the volcanic system (A. Okamura, individual
communication; Latter, 1981) .  It is possible that the waters emitted
from the hot fumaroles at Kilauea are related or identical to the waters
involved in such seismic events.  Although the stable isotopic
compositions of emissions of neither the hot nor the boiling temperature
fumaroles are remarkable in themselves, the details of the hydrogen and
oxygen isotopic compositions of the two types of fumaroles (hot, and
boiling point) indicate that there are two distinct regimes of water in
the hydrothermal system of the Kilauea summit region.  A segregation of
two components of the hydrothermal system at Larderello was recently
proposed by Petrucci et al. (1993).

Two decades ago, convincing demonstrations were made that fumaroles may be
universally dominated by meteoric water (e.g., Taylor, 1974).  Recent work
on active volcanoes, however, has proposed that waters of magmatic origin
do exist as significant components of hydrothermal and fumarolic fluids
(Bolognesi and D'Amore, 1993; Ciodini et al., 1993; Taran et al., 1991;
Giggenbach and Soto, 1992; Shevenell and Goff, 1993; Giggenbach, 1992a, b;
Blattner, 1993).  The initial chemical data on the hot Kilauea fumaroles
(high halogen and sulfur content, Gerlach et al., 1992), and their
placement at the possible epicenter of the Kilauea magmatic system,
suggested that they might prove to have a substantial, identifiable
magmatic water component.  The finding of the present study based on light
stable isotopic data that the hot fumarole waters are dominantly or
entirely meteoric in origin shows that it may be entirely inappropriate to
assume a magmatic origin of hydrothermal waters on the basis of chemical
composition alone.

CONCLUSIONS

Water condensates from new hot fumaroles at Kilauea have stable isotopic
compositions that indicate that they, like the common and long-studied
boiling point fumaroles of the Kilauea summit region, are mostly or
entirely meteoric water.  Any magmatic water component must be small.
Absence of tritium in the waters of the hot fumaroles indicates that they,
in contrast to the waters of boiling-point fumaroles, have been isolated
from communication with tritium-bearing atmospheric waters for more than
40 years.  The light stable isotope data indicate that the source of water
for the hot fumaroles is the catchment area on the slopes of Mauna Loa.
But the tritium data indicate that this water has been isolated from
contamination by young atmospheric water for the most recent several
decades or longer, during transport over distances of several kilometers
to the Kilauea summit area.  It is noteworthy, considering the unstable
tectonic environment of the Kilauea and Mauna Loa regions, and abundant
local rainfall, that these waters remain uncontaminated over such long
times, and long transport distances.  The overall hydrogen and oxygen
isotopic compositions of the waters of the hot and boiling point fumaroles
of Kilauea indicate that they are two components of the hydrothermal
regime that are not in mutual communication, and may be totally separate
and distinct.

Initial chemical information from the condensates of the hot fumaroles
(large sulfur, and especially halogen concentrations), together with their
central placement, seemed to indicate that they might have substantial
components of magmatic water.  The isotopic data indicate that the water
component of the fumarolic gas is still dominated by meteoric water.

ACKNOWLEGDMENTS

We thank M.T. Colucci for light stable isotopic analysis

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FIGURE CAPTIONS

Figure 1
Map of the Kilauea Summit Region, showing main Kilauea Crater, Halemaumau
Pit Crater with hot fumaroles, and boiling point fumaroles HMM and Sulphur
Bank.  Inset shows regions of island of Hawaii constituted by distinct
volcanoes (K, Kilauea; ML, Mauna Loa; MK, Mauna Kea; H, Hualalai; Ko,
Kohala).

Figure 2
Schematic drawing of apparatus for condensation of large volumes needed
for tritium measurement.  Placement of a silica glass tube inside the
titanium pipe, with an inner tube jacketed by a larger-diameter
reflectively-plated tube and with evacuated void space, was designed to
prevent early condensation, fallback and loss.  Loops immersed into a
water-and-ice bath served as a non-collecting preliminary cooler-
condenser.  Water condensing there was visibly swept on, and only a small
amount (<5 ml) remained at end of collection.  The main jar was immersed
in the bath only to a level below the lid, to preclude possiblity of
access of bath water through threaded seal into the sample.  Condensing
surfaces inside the preliminary loops and inside the first jar remained
far above bath temperature.  Some H2O was lost from the train, as
condensed drops (<5 percent of collected volume) and as uncondensed vapor
in amounts limited by partial pressure of water at ambient temperature at
sampling elevation (~0.035 atm).  Such lost H2O was inferred to be
depleted in the heavy isotopes relative to waters collected in the traps.
Apparatus used at cold fumaroles was identical except teflon tube was
inserted directly into the fumarole mouth.  Gases exiting the train were
mostly SO2 and CO2 (together ~50 mole percent of the gases emitted by the
fumarole, Gerlach, unpublished data).  Hot fumarole samples taken in 1991
used a simpler apparatus than that shown, without the insulated silica
tube at the fumarole mouth.

Figure 3
Hydrogen and oxygen isotope variation of condensates taken from hot and
cold fumaroles of the Kilauea Summit Region.  Also shown are corrections,
by three different models, to restore data to compositions of waters
originally emitted by fumaroles (see text).  Periods 1 and 2 were
successive collections at the W-3 fumarole.

Figure 4
Isotopic compositions of waters emitted by hot and boiling temperature
fumaroles, compared to magmatic water and to precipitation on the island
of Hawaii (Tilling and Jones; 1991; and in review 1993; International
Atomic Energy Agency data for composition of rain at Hilo for 1963,
weighted mean, 3.5 meters of precip.; elevation of summit of Mauna Loa is
3959 m).  Fumarole compositions shown are restorations, calculated by
three different models, to correct for sampling bias due to condensation
in collector (see text).  Magmatic water composition of lower part of box
from Sheppard, 1986 (Fig. 7); other data on magmatic water compositions
associated with rocks of specific compositional types can be found in
Taylor, 1986 (Figure 15 and Table 6).  Slopes and directions are shown for
processes that alter the isotopic compositions of waters.

October 21, 1994

Dr. W. F. Giggenbach
Institute of Geological and Nuclear Sciences
P O. Box 31 312,  Lower Hutt
New Zealand

Dear Werner

Please find enclosed our paper "Hydrogen and oxygen isotopic composition
of waters from fumaroles at Kilauea Summit, Hawaii", revised in accordance
with the suggestions of the two reviewers and yourself.

We have added to the discussion section of the paper to be more specific
about "magmatic water", its possible origins, some basics of the relations
between magmas and rocks, and the stable isotopes of hydrogen and oxygen.
The additions are in the second through eighth paragraphs of the
discussion section, on pages 7, 8 and 9.  We hope that this new material
satisfactorily responds to the queries of the reviewer who wrote the
single page of comments.  Five additional references follow from this
added discussion, at least one suggested by the reviewer.  Elsewhere in
the text we inserted a brief comment to clarify that sulfur and chlorine
have a magmatic source, whereas H2O may have multiple sources (re: query
[5] of the other reviewer, who wrote the longer set of comments).  In
response to the reviewer's mention of the Ingebritsen and Scholl paper, we
took another look at it, and confirmed our earlier impression that it does
not bear directly enough on volcanic and high-temperature hydrology to
warrant citing it in our paper.  Similarly, we decided not to specifically
address the matter of the importance of H2S in changing the deuterium
content of waters.

We think that our comment that our collection apparatus was designed to
get the large amounts of condensate needed for high precision tritium
analysis should satisfy the other reviewer's question (two sheets of
comments, his comment [2]) about why our newly designed apparatus was
needed.  We think that the zero tritium content of the condensate from the
hot fumarole should be enough to satisfy his query about contamination by
air, and by the water that might be contained by such air.  Comments [3]
and [4] by that reviewer, about isotopic and temperature effects from
water-rock interaction and about the meaning of "equilibrium", should also
be satisfied by the new paragraphs added to the discussion section (
above).  In response to this reviewer's comment [6], the 18O and D data
pairs in the Table for rain at two locations are not off by an order of
magnitude nor mixed up with one another: the isotopic compositions of rain
around the Big Island do not in fact always follow textbook systematics.

We moved the Appendix into the main body of the paper ("Site, sample
collection, and collection systematics" section) as suggested by the final
comment of the reviewer who wrote the single page.

We added more detail on the chemical composition of the condensates,
citing the proper reference.

We hope that you will find that we have responded adequately to the
comments of the referees, and that the paper is in satisfactory form to
proceed with publication in Bull. Volc.  If you have any additional
concerns, I will be in a position to respond promptly.

Sincerely

Todd Hinkley

tel: 303-236-5850 (voice); 303-236-1414 (fax); 303-355-2361 (dom.)
thinkley@usgs.gov

enclosures: the revised manuscript (???copies)
		"laser print" figures and table (blue envelope)
		copies of reviewers' comment sheets
		copy of letter from you
		disc, with ms. in Word for Windows, ASCII, and RTF