Jökull - 01.12.1963, Blaðsíða 15

Fig. 1. Geological map of the Mýrdalsjökull area.
Signature: 1. The younger grey basalts, 2. The Palagonite Formation, 3. Postglacial lava flows,
4. Sandur plains, 5. Glacier border. (After: Geological map of Iceland, by G. Kjartansson).
Eyjafjallajökull and Mýrdalsjökull (Fig. 1). Eyja-
fjallajökull itself is a volcano, which has been
active in historic times, the last eruption oc-
curred in 1821. The age of the massive is Quater-
nary to Recent, rnuch of the material being well
stratified palagonite tuffs and breccias. Petro-
logically the rocks range from ultrabasic ozea-
nites to basalts, but intermediate or acid rock
types are subordinate. The basaltic tuffs pre-
dominate indicating subglacial origin of much
of the material. The coastal regions south of
the massive were submerged during glacial
times, but since then the land has risen and
the glacial outwash continousiy extencls the
coastal line farther south.
FACTORS AFFECTING CHEMICAL COM-
POSITION OF GLACIER RIVER WATERS.
The chemical composition of natural waters
is determined by ion supply from the atmos-
phere and what is leached frorn rocks in contact
with the water (Gorham 1961). The atmospheric
supply is determíned by two factors, i. e. ocean
spray, which is earried down with the precipi-
tation, ancl gaseous compounds, rnainly COg,
which are dissolved in the water.
No detailed survey of the chemical composi-
tion of rain water and surface water in Iceland
exists at the present time, and it is difficult to
estimate the influence of this factor. Chemical
analysis of rain water from two weather stations,
one near the coast the other farther inland are
presented in Table 1. These analysis show vary-
ing amounts of chloride and sulfate. For the
subsequent discussion of the importance of this
factor as ion supply, these figures shoulcl be
looked upon as maximum values since snow
appears to be less effective in throwing down
the salt particles from the ocean spray than
rain (Gorham 1961).
The rock type in contact with the water is of
major importance in determining the water
chemistry Keller and Reesman (1963) give ex-
amples of the chemistry of glacier river waters
draining terrains of widely different rock types.
JOKULL 1963
11