Rit (Vísindafélag Íslendinga) - 01.06.1976, Side 134

fers would have to be derived from precipitation at a time when the
climate was much colder than today.
15. 5 Hveravellir.
Hveravellir is a high-temperature area in the western part of
central Iceland, located between the glaciers Hofsjökull and Lang-
jökull (Fig. 31, sampling point No. 20). Since there exist no drill
holes, the base temperature has not been measured directly, but the
silicate content of the water indicates that the base temperature
could be as high as 250°C (Amórsson 1970).
The measured 8D = — 94.7%0 for the spring water is the same as
found in the two big glaciers, but when corrected for possible eva-
poration as the water cools to 100°C on its way to the surface, the
value might be as low as 8D = — 100%0, which is actually some-
what lower than for any local groundwater found in this part of
the country.
Studies on the 415 m long ice core from the Vatnajökull glacier
have shown that the mean 8D-value of the precipitation during the
past several hundred years is about 5%0 lower than that for the
last 50-year period (see Fig. 13). It has also been found that the
retention time for the ice in Icelandic glaciers is at least several
hundred years on the average. Therefore, if the thermal water at
Hveravellir originates in either of the two glaciers Hofsjökull or
Langjökull, it is most likely derived from a precipitation about 5%0
lower in öD than the precipitation on which the deuterium map is
based.
The most reasonable explanation for the Hveravellir thermal
water is therefore that it originates in either of two areas, in the
northern part of Langjökull or the central part of Hofsjökull.
Whether the actual recharge area lies in Langjökull or Hofsjökull
cannot, however, be evaluated from the deuterium measurements
alone.
Another possible explanation for the öD-value of the thermal
water might be that the thermal system only receives water melted
on the glacier’s surface during the summer thaw. As discussed in
section 5.2, such meltwater would be significantly depleted in deu-
130