Depending on the context, volcanic eruptions are either terrifying or transfixing—sometimes both, but rarely neither. The opportunity to safely view the otherworldly spectacle of lava rarely fails to ignite a child-like, giddy wonder. The damage currently being done by a lava flows in the Cape Verde Islands, on the other hand, is heart-breaking.

We study these things because they are both lovely and terrible. We want to see a lava flow spill across a snowfield out of curiosity, and we want to better understand the hazards surrounding snow-capped volcanoes out of caution. Benjamin Edwards of Dickinson College and Alexander Belousov and Marina Belousova of Russia’s Institute of Volcanology and Seismology got the opportunity to witness one of these events last year in Russia’s Kamchatka Peninsula. For nine months, Tolbachik spewed basaltic lava flows that ultimately covered 40 square kilometers, reaching as far as 17 kilometers from their source.

The lava flows came in two flavors, known to geologists by Hawaiian names. (While frozen Kamchatka doesn’t exactly evoke coconuts and grass skirts, these lavas are similar to those of the Hawaiian volcanoes.) First there’s ʻaʻa (pronounced as a staccato “AH-ah”), which ends up a chunky, blocky crumble of basalt. The other is pahoehoe (roughly “puh-HOY-hoy”, which is how volcanologists answer the phone), which flows more like thick batter and can solidify into a surface resembling a pile of ropes.

The ʻaʻa lava flowed in tongues a few meters tall, tens of meters wide, and hundreds to thousands of meters long. The flows traveled like tank treads, with chunks of cooler basalt riding on top the liquid interior before tumbling off the front to be overrun and become the base. They crawled forward like this at around 1 meter per minute. The pahoehoe flows crept along at a little less than half the speed, but in a totally different manner. A bulb of lava would spill out from a crack and swell until it was maybe a meter wide or tall, at which point it would crack and unleash a new bulb headed in a slightly different direction. The whole mess would swell as interior flow continued, but with little bulbs leading the way.

The researchers observed these lavas as they flowed over snowpack up to 4 meters thick, making temperature measurements of the lava (carefully) and meltwater, and taking time-lapse photos to calculate flow speeds. They also dug several pits down through the snow in front of advancing lavas for another view of how the lava interacted with the snow.

You can see some of the researchers’ video below for yourself. Warning: giddy wonder likely.

You might guess that these red-hot lavas would burn through the snow almost instantly, reducing the surroundings to slush and steam. However, you’d be wrong. The ʻaʻa lava flows actually produced surprisingly little melt, though the snow beneath them would be gone in less than 24 hours. That’s partly because the blocky crust armoring the underside of the flow (at a cool 900 °C) insulates the snow from the hotter core of the lava. But it’s also because the snow, which contains so much air space, is a poor conductor of heat.

The pahoehoe flows were a different matter. Rather than rolling along atop the snow, they pushed down into it, producing some wild stuff— plowing up fractured blocks of snow, and even inflating domes beneath the surface that would then melt the snow above. This interaction produced more meltwater, which seeped through the snow and transferred heat much more effectively than the lava could do alone.

Even so, these flows were moving pretty slowly, and while the pahoehoe flows could produce some streams and small outbursts of meltwater, it wasn’t nearly enough to generate the kinds of dangerous mudflows common for more explosive eruptions.

The ʻaʻa flows didn’t end up looking any different than normal, but the pahoehoe flows wound up with a unique texture where they interacted with the snow, the researchers say. That’s pretty neat, because it could allow geologists to recognize old lavas that flowed over snow. If that volcano is not snow-covered today, you’ve learned something about past climate. The researchers point out it’s even possible we could recognize this texture in lava flows on Mars, where it’s thought that lavas may have flowed over ice in the past.

Nature Communications, 2014. DOI: 10.1038/ncomms6666 (About DOIs).