Carbon-dioxide springs may be more widespread than is now known. They are first and foremost known at Ölkelduháls, some quite large, that is, 10-20 m in diameter, with grey, murky ponds and a little outflow. There is gas and boiling turbulence in them in some places, but the ponds are otherwise of varying temperature. There are no deposits around them. The water in these springs is surface water from the lava above, but there is much carbon dioxide in the steam that heats them.
Found at: Innstidalur, Ölkelduháls, Ljósártungur
Calcareous crust
Calcareous crust is known in a few places in high-temperature areas where it is now cold or there is insignificant warmth in the springs. These places are on the outside of Selvallafjall (south-west of Trölladyngja) and in Blautukvíslarbotnar. In a few spots there are quite large deposits of aragonite, which is classed with calcareous crust.
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Carbon-dioxide springs and pools with calcareous deposits
Carbon-dioxide springs and pools with calcareous deposits occur in several high-temperature areas, especially at their margins, or where the activity is waning. The water in them is groundwater rather than surface water. Springs and pools of this kind are in Reykjadalur south below Ölkelduháls and east below Hengill (Hagavíkurlaugar). In Kerlingarfjöll (at Ásgarðsá), Tindfjallajökull (Hitagil), Kverkfjöll (Hveragil) and south below Torfajökull there are calcareous pools in several places as marginal phenomena (for example at Markarfljót, Bratthálskvísl and Hitalaug/Hólmsárbotnalaug).
Found at: Grímsnes, Kerlingarfjöll, Tindfjallajökull, Ljósártungur, Vonarskarð, Kverkfjöll
Carbonated springs
Carbonated springs are cold or just lukewarm springs found in high-temperature areas and often at their margins. They are usually iron-contaminated and bad-tasting, and the water reddish-brown, even so much as to colour entire streams (Rauðfossakvísl). Such carbonated springs are in the Torfajökull area, especially in the north-west, but also on the south side (Ölstallur) and east in Jökulgil (the Hraukar). They are also known in the Hengill area (Hengladalir), in Vonarskarð and as outflow inward from Grænalón. Water from the coldest of them, which bubble most from the carbon dioxide, is drinkable although it is brownish.
Found at: Trölladyngja, Innstidalur, Ölkelduháls, Kerlingarfjöll, Tindfjallajökull, Landmannalaugar, Jökulgil, Vestur-Reykjadalir, Austur-Reykjadalir, Ljósártungur, Vonarskarð, Þórðarhyrna