Rit (Vísindafélag Íslendinga) - 01.06.1976, Qupperneq 109

the respective recharge areas would be approximately 60 km. Con-
sequently the age of the thermal water in these areas would be
between 400 and 4000 years.
The longest possible distance for thermal water to flow under-
ground in the country would be when the thermal water pumped
out from the drill holes at Húsavík in North Iceland (see section
15.18.3) originates in the northern part of the Vatnajökull glacier.
This water would then have flowed underground for a distance of
approximately 150 km. Assuming an altitude difference of 700 m,
our calculations would give an average age of this water hetween
2500 and 25 000 years. The Húsavík water would then also be the
oldest groundwater which we expect to find in the country.
The above discussions can he summarized as follows:
The cold groundwater is obviously relatively young although
the age can vary appreciably. Local cold groundwater will hardly
be more than a few years old. Cold groundwater which has flowed
underground for longer distances can possibly he some decades old.
The thermal water, on the other hand, is usually much older
than cold groundwater. The age of the thermal water can obviously
vary greatly, depending on various parameters such as the distance
the water has flowed underground, the permeability of the rocks,
and the hydraulic gradient. The youngest thermal water is likely
to be only a few decades old on the average, and in almost every
case the age of the water must he less than 8000 years. This is
supported by the fact that in all cases, except in one thermal system,
the water has a 8D-value comparable to that in the present-day
precipitation. In exceptional cases, i.e. when the water may have
flowed underground for a distance of up to 150 km, the thermal
water could be as old as from the time of last glaciation. This could
be the case if the water flows underground from the northern part
of the Vatnajökull glacier to the Húsavik area. In fact the Húsavík
thermal water contains less deuterium than any present-day pre-
cipitation in Iceland.
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