Jökull - 01.12.1983, Blaðsíða 86
to be considered for the diíferent types of hlaups, i.e.
involving purely melt water, as in Graenalón
(.Bjömsson 1976), hydrothermally derived melt
water, as in Grímsvötn or Skaftá, and hlauþs
associated with volcanic activity, such as Katla
(Thorarinsson 1975) and in part Grímsvötn:
Type 1 - meteoric. If chemically detectable at all an
initial decrease in dissolved abrasives should be
observed together with an increase of precipitation-
derived ions. If high altitude precipitation is involv-
ed an overall decrease in dissolved load would sup-
posedly be observed.
Type 2 - hydrothermal. An initial increase in
carbonate and sulphate (sulphide) would be
expected, especially for activity of high temperature.
If thermal water is involved, sodium would also be a
feasible monitoring ion (Fig. 3).
Type 3 — volcanic. Only the gaseous species
dissolved in the fluid can be recommended for
monitoring in the purely-volcanic system, since the
degassing of ascending magma would release gases
regardless of geothermal activity near the surface.
Carbonate (pH) is undoubtedly the easiest monitor,
although sulphate(SO|'derived from S02), dissolv-
ed hydrogen (redox monitor), and the noble gases
all might come into consideration.
ACKNOVVLEDGEMENTS
We are indebted to Drs. S. Amórsson, H. Bjömsson, Sv.
Björnsson, E. Gunnlaugsson, and G.E. Sigvaldason for
reading an earlier version of the paper and contributing
valuable crilicisms and imþrovements. The 1972-series of
samples was collected by Mr. Ragnar Stefánsson of Skafta-
fell; the other samples of Skaftá and Skeidará wereprocured
by Mr. Sigurjón Rist, hydrologist at the State Energy
Authority.
REFERENCES
Armannsson, H., H.F. Magnússon, P. Sigurdsson, and S.
Rist 1973: Efnarannsókn vatns. Vatnasvið
Hvítár — Olfusár; einnig Pjórsá við Urriðafoss,
1972. (Chemical analysis of natural water in the
drainage area of Thjórsá and Hvítá, 1972). OS,
RI, Prof. Paper, 8 pp. + Tables + Figures.
Mimeographed (in Icelandic).
Arnason, B., H. Björnsson, and P. Theodorsson 1974:
Mechanical drill for deep coring in temperate
ice. J. Glaciol. 13: 133-139.
Amórsson, S. 1979: Hydrogeochemistry in geo-
thermal investigations in Iceland: Techniques
and applications. Nordic Hydrology 1979: 191-
224.
Amórsson, S. 1980: Efnahitamælar (Chemical geo-
thermometers). Náttúrufr. 50: 121-138. (In Ice-
landic with English abstract).
Amórsson, S., S. Sigurdsson, andH. Svavarsson 1982: The
chemistry of geothermal waters in Iceland I.
Calculations of aqueous speciation from 0° to
370°C. Geochim. Cosmochim. Acta 46: 1513-
1532.
Bjórnsson, A., G.Johnsen, S. Sigurdsson, G. Thorbergs-
son, and E. Tryggvason 1979: Rifting of the plate
boundary in North Iceland 1975-1978. J.
Geophys. Res. 84: 3029-3038.
Björnsson, H. 1974: Explanation ofjökulhlaups from
Grímsvötn, Vatnajökull, Iceland. Jökull 24: 1-
26.
Bjórnsson, H. 1976: Marginal and supraglacial lakes
in Iceland. Jökull 26: 40-51.
Björnsson, H. 1977: The cause of the jökulhlaups in
Skaftá River, Vatnajökull. Jökull 27: 71-78.
Bjömsson, H., S. Bjömsson, and Th. Sigurgeirsson 1982:
Penetration of water into hot rock boundaries of
magma at Grímsvötn. Nature 295: 580-581.
Fournier, R. 0. 1977: Chemical geothermometers
and mixing models for geothermal systems. Geo-
thermics 5: 41-50.
Foumier, R.O. and A.H. Truesdell 1973: An empiri-
cal Na-K-Ca geothermometer for natural wat-
ers. Geochim. Cosmochim. Acta 37: 1255-1275.
Fridleifsson, I. B. 1979: Geothermal activity in Ice-
land. Jökull 29: 47-56.
Helgeson, H. C. 1969: Thermodynamics of hydro-
thermal systems at elevated temperatures and
pressures. Am. J. Sci. 267: 729-804.
Lawrence,J.R.,J.R. Drever, T.F. Anderson, and H. K.
Brueckner 1979: Importance of alteration of vol-
canic material in the sediments of Deep Sea
Drilling Site 323: Chemistry, l80/l60 and 87Sr/
86Sr. Geochim. Cosmochim. Acta 43: 575-588.
Rist, S. 1954: Skeiðarárhlaup 1954 (Jökulhlaup in
Skeidará 1954). Jökull 5: 30-36 (in Icelandic
with English abstract).
Rist,S. 1973: Jökulhlaupaannáll 1971, 1972 og 1973
(Jökulhlaups in theyears 1971, 1972, and 1973).
Jökull 23: 55-60 (in Icelandic with English
abstract).
Rist, S. 1974: Efnarannsókn vatna. Vatnasvið
Hvítár — Olfusár; einnig Pjórsá við Urriðafoss,
1973. (Chemical analysis of natural water in the
drainage area of Thjórsá and Hvítá, 1973).
OSV7405, 11 pp. + Tables + Figures.
84 JÖKULL 33. ÁR