Ahead lies an impossibly steep curving wall of solid rock, 460 feet high; to the left, a craggy, broken crater – a tephra ring about fifty yards across. A tephra ring is a partial crater formed as exploding volcanic ash falls to the ground in a semicircle, usually molded by the prevailing winds, which on Surtsey can be fierce. Geology-speak is a Babel of languages. Tephra is Greek for ash. Lava is Hawaiian. Many other terms are Icelandic, which is among the oldest continuously spoken languages in the West, the language of the Sagas, and, at times, the language of geology.
Lava, in Icelandic, is hraun. “It’s the oldest word for lava there is,” Jim says. There are several subsets of hraun: apalhraun, which is rough lava, and helluhraun, which is smooth. A small volcano in Icelandic is a dyngja. Hlaup means “flood,” and jökull means “glacier.” If you put those two words together – jökulhlaup – you get something for which there is no exact equivalent in English: a catastrophic outburst flood caused by water trapped under a glacier, which cracks open the ice and violently disgorges.
This catastrophic event occurred in 1993 on an Icelandic flood plain called the Skeidararsandur. Blocks of ice as large as houses tumbled for miles across the flooded black primeval landscape in an orgy of geologic violence. A similar geological disaster also occurred on Mars in the distant past. The scale was immense. It is estimated that the Martian jökulhlaup released as much as 100,000 cubic meters of water per second, more than the entire flow of the Amazon river.
At the moment, we are standing on hraun, or, more precisely, helluhraun, with a little apalhraun scattered here and there. Looking into the tephra ring, Jim says he’s stunned “to observe the development of erosional canyons massive enough to drive a Hummer through.” He didn’t see anything like this on his last trip to Surtsey. The erosional scars remind him of features shown in the latest images from Mars Orbiter Camera, now circling the Red Planet.
“These mini-canyons, technically erosional gullies, expose the underbelly of Surtsey, the volcano. They give clues about its future and the processes that formed it. The sheer beauty of these signs of geologic aging and their abundance are remarkable!” He takes a closer look at the black windblown tephra. “See how it’s sorted? See how the small rocks have risen to the top? That sorting is common. Some of them are rounded.” Those smooth contours, he tells me, are diagnostic of wind and water, and he looks for similar shapes on Mars. “So far, we haven’t found a lot of really rounded ones on Mars,” he admits. But he keeps looking because evidence of water is essential to the detection of life beyond Earth. In fact, water has assumed such importance that the question of extraterrestrial life has been reframed; where scientists once inquired, “Is there life elsewhere in the universe?” they now ask, “Is there liquid water elsewhere in the universe?”
Many planetary geologists, Garvin included, now see convincing evidence that Mars once had lots of water, and may still have a tremendous amount of water even now. Their goal is to follow the water because they hope it will lead them to life. So they seek distinctive water signatures. They look for evidence of dried-up rivers and oceans and shorelines; they theorize about subsurface water, and they measure glaciers – anything associated with water.
Stepping lightly on tephra, Jim makes his way across the eastern side of the island, squinting and kneeling, taking measurements, orienting and reorienting himself, studying the landscape, observing the reverse sorting of the soil, in which “coarser fragments the size of popcorn nubs rise to the top of the soil horizon, leaving the finer, claylike fraction below.” He notes the fragmentation of large blocks of volcanic rocks. On the right, Jim confronts a landscape studded with pitted blocks ranging in size from softballs to basketballs. Those pits grab his attention. He spent a good deal of his graduate career at Brown in the mid-1970s studying patterns of pits and surface textures on terrestrial rocks and on Martian boulders photographed by the two Viking landers, trying, as he put it, “to unravel the geologic secrets of Mars.” Here is a banquet of strikingly similar boulders, on which he is ready to feast. He notes unpitted gray rocks with angular shapes – so-called “country rocks” – as well as pitted rocks, whose morphology speaks to him, telling of displacement from a lava flow.
Jim explains how this local landscape came to be: “Once the sea water was kept out of where the lava was bubbling up, a carapace of lava formed. And that lava is very important, because it protects the vent. The vent is where the hot rock comes up. That is the reason this island survives today.” He displays what looks to me like an ordinary rock, but to Jim, it’s a geologic sonnet. “This is tephra that tumbled downhill. See how it’s made up of bits of other stuff? It’s actually a breccia. A breccia is stuff made of other stuff, little welded bits as strong as concrete.” As I hold the raw geological material in my hand, Jim reminds me that this is what the rocks on Mars look like; the main difference is that they’re coated with a brown dust. He feels around the edges. “It’s a smooth little rock,” he says. “That means it’s been worn by erosive agents, so we look at the rounding of the corners to get an indication of what’s going on.” I carefully replace the rock so as not to disturb the course of Surtsey’s geological evolution.
The hraun we traverse feels like soft beach sand. Jim tells me that on Mars, the soil is ten times finer than what we’re walking on now. “It would be more like walking on talcum powder.”
We press on, and the terrain subtly shifts. “Now we have coarse stuff lying on the surface,” Jim remarks, as he tries to read the landscape. “Here’s a little piece of basaltic pumice. That’s a good one,” he says, slipping it into his pocket, which is, perhaps, not quite kosher. “That’s one for the spectrometer,” he explains. There’s an honor system in force here. You’re not supposed to disturb anything. You try not to leave footprints in this haven for scientists if you can possibly avoid it. “Now, this looks like – aha! This –” he announces, “is a little lava bomb.”
“What?”
“A lava bomb is something that flew through the air and went splat! And then it started to break. Already, it’s weathering away. See how it’s crumbling. Again, this is what we looked for at the Pathfinder landing site.” He calls my attention to smooth rocks inside smooth rocks, and he begins to interpret. “You can piece together the history of this rock,” he says. “These rocks were always smooth; they got pasted together at the time of the eruption.”
He sees some similarities between the geology underfoot and the Pathfinder landing site on Mars. NASA sent Pathfinder to a location on Mars where it was believed that a great outpouring of water once occurred. “Some people think the rocks in Pathfinder’s vicinity came to rest there as the result of one big flood, but that’s ludicrous. It’s a mixed population of rocks around Pathfinder,” which suggests, to him, at any rate, that the geological history of the area has been fairly complex. Water might have come and gone around the Pathfinder site more than once over the eons. I look around; if you photographed a replica of Pathfinder here on Surtsey, you could persuade a fair number of people that the spacecraft was actually on Mars. The more Jim talks, the more I feel a geological kinship between the two planets; Mars seems so Earth-like, or is it more accurate to say that Earth is so Mars-like?
Garvin kneels to inspect a delicate lava formation. “See the thin carapace of lava? This black stuff?”
“It’s very soft.”
“Right, very soft underneath.”
“It’s falling apart.”
“Not all of it. And that’s important, because that’s the action of a process that tears down rocks and makes clays. We take clays for granted. On Mars, there’s likely to be a lot of clay.”
“And water is necessary for clay.”
“Yes. You have to break rocks. Look at this.” He points to where the hillside is collapsing. “What you see is little mudflows. And look at this. Here is a beautiful little lava rock! Very angular. This is a classic, coated with fine-grain stuff. It’s