For those living in the comfort of the temperate mid-latitudes, defining ice seems simple: It’s frozen water. The ice cube trays in our freezers, filled from the faucet and left to solidify, attest to that. So too does the thin film of ice that forms mid-winter on streams or city streets, a slippery sign that the temperature has rendered liquid into a hazardous solid. But with a small change in latitude or elevation—or timescale, for that matter—ice takes on a different property, shifting from being the cold cousin of water to the coldest form of rock. At large spatial and temporal scales, ice is capable of contouring land, of covering oceans, and of vast destruction and construction: It is a geomorphological force to be reckoned with.
That ice is a rock is not metaphorical. Just over a hundred years ago, in 1917, Lieutenant J. M. Wordie—a scientist aboard the Endurance expedition of 1914–17, captained by Ernest Shackleton—reported to the Royal Geographical Society the scientific observations that were taken while the ship was trapped by Antarctic pack. Wordie’s observations of ice were deeply geological. He spoke of sedimentation and striae, and distinguished types of ice through careful observation of the “structure, salinity, and specific gravity” of the frozen matter.1J. M. Wordie, “The Drift of the ‘Endurance’,” The Geographical Journal 51, no. 4 (1918): 216–30; on 220. Amongst Wordie’s audience on that chilly December afternoon was Captain Douglas Mawson, another well-known polar explorer who had accompanied Shackleton to Antarctica eight years earlier. Wordie’s discussion of ice piqued his attention and compelled him to jump in to reiterate. “One cannot emphasize too strongly that ice is rock in a geological sense,” he explained. Ice “is to be treated petrologically as such. It is a rock in which there is a vast excess of one substance”: water.2H. R. Mill, J. M. Wordie, Douglas Mawson, T. Orde Lees, R. C. Mossman, R. N. Rudmose Brown, and Mr. Hinks, “The Drift of the ‘Endurance’: Discussion,” The Geographical Journal 51, no. 4 (1918): 230–37, on 231. Today, earth scientists agree with Mawson’s assertion. While a very weak plastic solid (it can and does quickly change state and begin to flow), ice is a monomineralic rock, metamorphized from the solidification of hundreds of thousands of snow crystals.3Monomineralic here means a rock which is 90 percent comprised of a single mineral. So, ice is more akin to pure marble (formed from calcite) than it is to granite, which forms from the amalgamation of different minerals.
This reminder of rocky ice is particularly pertinent in our increasingly hot historical moment, where the material is understood as an interlocutor for the climate crisis: seen as fragile and liminal, always about to dissolve into a liquid state. Janus-faced, ice-as-rock suggests that it is in fact equally as liable to expand and smother. Ice, therefore, emphasizes the multiplicity of water, and the multiple temporalities that multiplicity embodies. In so doing, it rearticulates the capricious and unpredictable nature of water, which, in all its states, speaks to humans of the limits of their control, through space and through time.
The exteriority of ice
While Wordie and Mawson were two of the first men to sail south and encounter Antarctic ice in all its immensity, they were far from the first to consider the rock-like qualities of frozen water. By the 1830s, naturalists were fascinated by the glaciers in the Swiss Alps and Scandinavia, and began gathering observations in attempts to explain how it was that these frozen rivers moved, that is, to understand the physics of ice. The complexity of a “hot,” frozen solid—a solid that hovers close to its melting point—drove intense debate: Did ice flow as one mass over the bedrock of the mountain? Or, did ice change state in its interior, moving as a viscous or plastic, faster in some regions than others? Meanwhile, far from mountain tops or the polar regions, the effects of ice were unwittingly being studied by geologists as they sought an explanation for erratic rock distribution on the lower, ice-free landscapes of Scotland and England. A theory of the Ice Age, popularized by Louis Agassiz, transposed the dynamics of high mountain glaciers onto familiar lowlands: As the movement of ice was understood, the past effects of far larger sheets of ice, now retreated, were recognized on the landscape. Life in the more temperate zones, it was discovered, was taking place in the negative mold of long-melted ice.
Thinking of ice as a rock brings different stories and histories into sharp relief, as the scope of water swells through space and time. Spatially, it pulls our minds to the poles—distant places for the majority of the human population. On the vast ice sheets of Greenland and Antarctica, the capacity for ice to reconfigure a landscape is self-evident: Thousands of feet thick, the topography beneath the sheets are all but obscured by the slowly flowing mass. But thinking of ice as rock can also pull us through time, just as it did for naturalists in the nineteenth century. Take New York City, for example. The bustling metropolis is situated at what was the southern edge of the Laurentide ice sheet, which, through the last Ice Age, covered much of North America for millions of years, expanding and contracting slowly until it retreated 18,000 years ago. The city and surrounding landscape are geologic relics of this ice: erratic rocks sprinkle Central Park, a ridge of rubble runs through four boroughs, and the fifth, Staten Island, is the tip of the ancient glacial moraine now known as “Long Island.”
The interiority of ice
As swiftly as rocky ice can transport us to a temporally distant past, so too can it bring remnants of that past to our present. The short-term preserving power of ice has become mundane in contemporary life, pervading our kitchens, grocery stores, food chains, and laboratories. But the expansive temporal range of the substance is most visible where ice collects at scale. If ice is a rock, then like a rock, depth denotes age. Just as the sedimentary rock of the earth’s crust forms through deposition, with layers of new material settling upon the deeper and older matter, ice sheets form in horizontal layers. But where layers of rock strata form over eons, ice layers reflect an annual cycle of warming and cooling. As temperature changes the composition and consistency of crystals, distinct summer and winter layers form. Polar ice sheets are thus an accumulation, hardened and compressed over time, of water long trapped in a frozen state, neatly recording annual seasonal flux.
The great tabular icebergs that fracture off the planet’s ice sheets reveal this vividly. Composed of horizontal striations, these ocean cliffs—some so large they have hosted scientific research stations—are echoes of desert sandstone, with ochres and reds replaced by a bright and hardened blue. In the nineteenth century, these icebergs were useful messengers of what lay ashore: While reaching the southern continent proper proved elusive, parts of the Antarctic ice shelf would fracture off, and drift north to more navigable seas.
When the Challenger undertook its famous oceanographic expedition in the 1870s, the crew encountered these vast tabular bergs, that, like other landscapes and specimens, they carefully photographed and described. To those interested in ice sheets—notably Scottish naturalist James Croll, who had developed a viable theory of the cause of the ice ages—the reports and images of the bergs revealed them to be natural chronometers. “The blue bands,” he wrote, “represent portions of the snow surface which during the heat of summer becomes partially melted and refrozen into compact ice; while the intervening portions represent the snow of the greater part of the year.”4James Croll, “The Ice of Greenland and the Antarctic Continent Not Due to Elevation of the Land,” London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science 16 (1883): 351–360, on 355. The multiplicity of annual layers gave a sense of the age of the Antarctic sheet from which the icebergs had sloughed off. Croll hypothesized that “judging from the number of these layers in an iceberg some of these layers must be of immense age, occupying a period probably of several thousand years in their formation.”5Ibid. This stratigraphic reading—lifted from rock on land and applied to ice at sea—holds true: From icebergs to pit studies to ice cores, the vertical dimension of ice is an axis through time.
But frozen water brings from the past more than a story of annual freeze and thaw. Through the twentieth century, advances in analytical methods, in particular radiocarbon dating and geochemistry, have revealed even more temporal complexity in the frozen depths. Geochemistry looks beyond strata to the elemental components of rocks: Each rock is a chemical system, and at the same time is a component part of the broader geochemical system of the earth (and the cosmochemical system of the universe). Using trace elements and isotopes as guides, geochemists have followed “the distribution and migration of the chemical elements within the earth in space and in time.”6Brian Mason, Principles of Geochemistry, 3d. ed. (New York: Wiley, 1966), 4. The result is an image of a porous earth, through which elements flow in different materials and states. To access water from millennia ago is to gain access to the geochemical vagaries of the past earth, a snapshot of chemical compositions that have long-since realigned. In ice cores, the annual strata are therefore just the first temporal signifier: By training a mass spectrometer on old water crystals, a vibrant picture of the past comes into focus. And, contained within the ice, there are fragments of other components of the environment, like air bubbles, cosmic dust, pollen spores, and meteorites. As scientist Roger Revelle put it in 1957 as the research undertaken during the International Geophysical Year had begun to reveal the scientific value of deep ice cores, the material is “a kind of library of what has happened in the past, locked up and frozen.”7Roger Revelle testimony in “Report on International Geophysical Year,” Hearings before the Subcommittee of the Committee on Appropriations House of Representatives, Eighty-Fifth Congress, First Session (Washington, DC, United States Government Printing Office, 1957), 105.
Rethinking ice as a rock therefore imparts an additional dimension to water, one characterized by a multiplicity of temporalities and by an attentiveness to state-change. On the one hand, as a geomorphological force that ebbs and flows through millennia, ice draws attention to how utterly dwarfed by deep time we are: Even far from the poles, rocky ice shaped the land beneath our feet. On the other hand, as a geochemical container that holds still morsels of the past and transports them into the present, ice collapses the distance between deep and shallow time, flexing an impressive capacity for preservation. This temporal multiplicity is materialized in the very precarity of being in a frozen state. Hovering on the precipice of tangible, seemingly permanent solid and ephemeral, unbounded liquid—a metamorphosis from rock to water that happens with the increase of a few degrees—ice powerfully articulates that water can and does exist in many forms, and at many spatial and temporal scales, at once. Ice thus brings the past to the present by being a defiant form of water, one that stays steadfastly still. While the rest of the hydrosphere swirls and changes at pace—as oceans mix, rain falls, rivers meander, and lakes drain—ice slows down, and in so doing, it captures time.
Banner photo: Caroline Landau, Svalbard Arctic Circle Residency, 2017.