We visited Víðgelmir lava cave in the morning and continued to Hraunfossar and Barnafoss in the afternoon. The day had intermittent rain, and we ended up back at our campground in the Húsafell hotel area.

Víðgelmir

Víðgelmir is the largest lava cave in Iceland by volume. It formed during the eruption that laid down the Hallmundarhraun lava field a little over a thousand years ago, when a river of molten lava crusted over on top, kept flowing underneath, and then drained out, leaving the tube behind. The cave runs about a mile into the field, with sections up to 52 feet high and 54 feet wide. Entry is only allowed with a guide, since earlier uncontrolled visits damaged some of the formations.

The names here carry the folklore. The lava field, Hallmundarhraun, takes its name from Hallmundur, a giant in Grettis saga. In the story Hallmundur steps in to defend the outlaw Grettir during a fight, then takes him in at a cave where he lives with his daughter. That saga cave was long imagined to lie somewhere in this field. A neighboring cave carries the same weight: Surtshellir, named for Surtur, the fire giant of Norse myth. The land here was one early Icelanders filled with giants and outlaws living underground, and the setting fits, since the caves really did shelter people.

Our guide explained that bones and a leather purse from the Viking Age were found inside the cave in 1993, dated to roughly the first century after the eruption. Someone used the cave as a shelter or hiding place not long after Iceland was settled, which is the real version of the outlaw folklore.

Deeper in, the walls carry mineral deposits in bands of color, mostly reds and yellows from iron and sulfur, left as the lava cooled and later as water moved minerals through the rock. Reds, yellows, and near black sit side by side depending on what concentrated where.

The variety of formations was the real surprise, several of which we had never seen before. In places the walls look glazed, as if coated in dripping candle wax or melted chocolate, which is lining that ran molten down the rock and froze mid-flow. On the floor were lava roses, blobby flower-like mounds built up where molten lava dripped from the ceiling and solidified in a pile, the same formation we had seen in a lava tube in Hawaii. Near them were lava candles, drip stalagmites that build up as a taller cone where lava keeps dripping on one spot, looking like wax pooling under a burning candle. In colder parts of the cave there were also ice stalagmites, water that seeps in and freezes into cones on the floor, mimicking the shape of true stalagmites but made of ice rather than rock.

The guide also pointed out bacteria growing on bare rock. What makes them worth mentioning is how they live: no light, no outside food, no water needed. They pull their energy straight from the minerals in the stone, a process called chemolithotrophy, literally feeding on rock. That ability is why lava tubes like this one interest astrobiologists. NASA studies microbes in volcanic caves in Hawaii and the American West as stand-ins for Mars, where lava tubes exist, the surface is hostile, and the subsurface might not be.

The cave also has lava straws, thin hollow stalactites hanging from the ceiling, formed when trapped gas forced molten lava out through a small opening and blew it into a hollow tube before it froze. We had seen straws before in a cave in the US, Kartchner Caverns in Arizona, which holds the record for the longest one at over 21 feet. But those are a completely different thing. A soda straw at Kartchner is calcite, built slowly downward over thousands of years as mineral-rich water drips through a hollow tube and leaves a ring of stone behind at the tip. A lava straw forms in the opposite direction and in a matter of hours, as gas-driven molten lava hardens in place. One is water depositing mineral over millennia, the other is rock freezing mid-drip. They only look alike.

From the high ground near the entrance we could see Langjökull, Iceland’s second largest glacier, in the distance, with the mountains stepping up toward it. That glacier turned out to be the connection to our next stop. Meltwater from Langjökull sinks into the Hallmundarhraun lava field and travels underground through the porous rock, so we left the cave and drove a short way to where that same water comes back to the surface, at the waterfalls.

Hraunfossar and Barnafoss

Hraunfossar has an appearance unlike almost any other waterfall. There is no river running along the surface and dropping over a ledge. Instead the water springs straight out of the rock face along the bank, a run of small clear streams emerging directly from the lava over a stretch of about 3,000 feet before feeding into the Hvítá river. Meltwater sinks into the porous lava and flows underground until the Hvítá, running alongside, has cut its channel down through the lava to the solid impermeable rock beneath. Where the river has exposed that boundary, the groundwater has nowhere to go but out, and it spills from the wall as dozens of springs. This is the same underground flow we had walked through at Víðgelmir. It runs against the usual Icelandic pattern, where waterfalls are surface rivers dropping over basalt ledges. Here there is no surface stream at all until the water reappears at the river’s edge.

The water is a clear cold spring by the time it emerges, filtered through miles of lava, which gives it a strong blue-green color against the dark rock. That color is the reason the falls are protected, designated a national monument in 1987.

A short walk upstream is Barnafoss, where the Hvítá squeezes into a narrow gorge and turns violent, a complete contrast to the quiet springs just below it. The name means “Children’s Falls,” and it comes from a folktale recorded on a plaque at the site. The story goes that the household at the nearby farm of Hraunsás left for Christmas mass, leaving two children at home with instructions to stay. The children grew bored, went out, and tried to follow their parents by crossing a natural stone arch that then spanned the gorge. They fell into the river and drowned. When the parents returned and traced the children’s tracks to the arch, the mother had it destroyed so no one would meet the same fate. Some versions say she cursed it instead, and that an earthquake later brought it down. A natural rock arch still stands over the gorge today, though it is not the one from the story.

Whatever the truth of the legend, it fits the setting. The two waterfalls sit within a short walk of each other and could not be less alike: one a silent seepage of spring water out of a wall of lava, the other a hard, loud rush of glacial river through a slot in the rock.

The rain held off while we were at the falls, which made the walk between the two viewpoints easy. We got back to the campground at the Húsafell hotel area in the evening. On a day when the weather kept changing, a cave tour followed by a short walk to two waterfalls turned out to be a good pairing, since neither one needed clear skies.