ON THE GROUND

Zoe W. Morrisonread bioZoe is a landscape and urban designer in New York City. She was raised in Beijing, China.

In the summer of 2023, the Philadelphia Streets Department resurfaced my street. Beneath the covering layer of asphalt were strips of cobblestone, layers of brick, bits of aggregate and crushed stone that presented like seashells. The cobblestones were intact, their binding still holding them together. Suddenly, the street had a texture, a sense of time and material, the dappled light oceanic across the cobblestones.

In his book The Eyes of the Skin, Finnish architect Juhani Pallasmaa writes that natural materials like stone, brick, and wood “allow our vision to penetrate their surfaces and enable us to become convinced of the veracity of matter… All matter exists in the continuum of time; the patina of wear adds the enriching experience of time to the materials of construction.”¹ It is in the absence of natural material, and the presence of machine-made materials of scale-less glass, enameled metal, and synthetic plastic, that we experience an absence of connection to time or to place. This matters to our human experience because the architecture of our surroundings, our cities and towns and their infrastructure, are among the things, along with seasons, aging, relationships, that enable us to, “perceive and understand the dialectics of permanence and change, to settle ourselves into the world, and to place ourselves in the continuum of culture and time.”²

The flatness that pervades much of our built environment has become a central condition of modern life. The sameness of material culture has become so total that it operates on a scale that is globally legible. As this process of material homogenization nears completion, we observe the trail of material artefact left in its wake. We recognize the accumulation of detritus both at the register of small single-use objects—thin plastic bags, polyester shirts, 16.9 oz 100% Natural Spring Water bottles—and at the scale of growing mounds of construction debris such as long strips of veneer tiles, blue-green heat-strengthened glass from demolished skyscrapers, and chunks of concrete panels. Alongside these waste streams mounts a growing sense of detachment from our surroundings. The ubiquity of certain materials, with asphalt as a primary example, only adding to the sleek, frictionless built world. The texture of our contemporary streets recapitulates into perfect facsimiles: the asphalt of Toronto the same as the asphalt of La Plata, the same as the asphalt of Hangzhou. Materiality devoid of any specificity, this urban condition leads us to a hollow, flat, and noxiously superficial experience of being in place and time.

Returning to the ground of Philadelphia, the uncovered cobblestones feel like tiny portals; I listen to the sounds of hooves, rickety wheels, and see remnants of small tassels of wet mosses growing across the stones. These stones lay, like a rose-pink wound, freshly uncovered from the ubiquitous skin of asphalt. I had not yet reconciled the pervasive imprint of asphalt on my daily experience until I was confronted by its absence. Unlike the cobblestones, with their historic associations and romantic conjuring, asphalt was simply a modern waste whose material category registered on the level of synthetic byproduct analogous to plastic faux-wood applique, asbestos-laden veneer tiles, a material treatment devoid of any specificity.

Yet, this instinctive categorization of the material is at odds with the legacy of its discovery and use. Asphalt is oddly historical, tying us across human development to ancient civilizations. In looking into the black pitch of the asphalt surface we gain access to geological history and an entry into deep time. It is spatially traceable, stemming from sites with geologic conditions interacting with organic material under pressure over millions of years to give rise to the natural deposits where bitumen occurs. The material history of asphalt and its use is strangely complex and temporally rich. Its material present is equally as complicated; with far reaching spatial implications. Despite its ubiquity, with asphalt covering somewhere around 260 billion square meters of earth, it retains a specificity of origin and place.

THE MATERIAL PAST (DEEP TIME)

The word ‘asphalt’ references this spatial origin—derived from Ancient Greek, ἄσφαλτος, or ásphaltos, the ancient Romans knew the Dead Sea as the palus asphaltities, or “asphalt lake.” With huge blocks of asphalt, up to 100 tonnes in weight, found floating on the lake; these are referred to as the “bulls” of the Dead Sea. The emergence of these massive slabs would prompt a swarm of seamen to race towards the asphalt, axe in hand, to cut off pieces and load the asphalt onto camels for the journey to market in Alexandria. These slabs are composed of the once-living material of marine plants and animals that died millions of years ago. Such deposits of asphalt are found in lakes, including Lake Bermudez in Venezuela and Pitch Lake in Trinidad and Tobago. The latter became the focal point of a pivotal moment in industrial history: in 1887, American businessman Amzi Barber—then known as the “Asphalt King”—struck a deal with the colonial British government to extract asphalt from Pitch Lake. By 1900, he had laid more than twelve million square yards of pavement in seventy U.S. cities, including New York City and Washington, D.C., all sourced from the Trinidadian lake.³ Asphalt is found in the seeps of the La Brea Tar Pits and the McKittrick Tar Pits of Southern California, and it also exists in vast quantities in the tar sands of the Peace–Athabasca Delta in Alberta, Canada; the Faja Petrolífera del Orinoco in the Orinoco River Basin of Venezuela; and the Uinta Basin of Utah. The term asphalt is used interchangeably with bitumen to mean both natural and manufactured forms of the substance. Geologists prefer bitumen to connote the natural, unprocessed substance; its etymology is pitch, which became pichument and later bitumen. The vast majority (85%) of bitumen extraction and refinement worldwide is used in the creation and maintenance of roads, runways, parking lots, and paths.⁴

Use of bitumen by humans dates back to at least the fifth millennium BC, when it was used to coat a crop storage basket in Mehrgarh, a Neolithic archaeological site located on the Kacchi Plain in Pakistan.⁵ Prehistoric hunters and farmers used the sticky material for creating tools—affixing flint spearpoints to shafts or attaching stone edges to sickles for harvesting.⁶ It is believed that the earliest paved street was built in 1200 BC by the Hittites in Bogazkale in Central Turkey.⁷ Six hundred years later in Babylon a Processional Way named The Street On Which May No Enemy Ever Tread was constructed by Nebuchadnezzar and inscribed with the words, “glistening with bitumen and burnt bricks.” It was paved with limestone flagstones and bricks then mortared together by lime and bitumen.⁸

Bitumen was used extensively in waterproofing, covering the Great Bath of Mohenjo-daro, the earliest public water tank of the ancient world.⁹ It was used by the Sumerians for ship caulking and waterproofing.¹⁰ The ancient Egyptians mixed bitumen with aromatic resins for use in mummification, creating a high demand for bitumen in the region. The advent of this particular use of the material prompted fighting in the year 312 BC between the Nabataeans who controlled access to the Dead Sea and were, at the time, the sole exporters of Dead Sea bitumen to Egypt, and the Greeks sought their own source—this is considered one of the first known battles for a hydrocarbon deposit.¹¹ Bitumen was used as mortar in Babylon’s city walls and pavements composed of brick or limestone mortared with bitumen have been found in Khafaje, Heet, Assur, and Babylon.¹² Maxwell Lay, John Metcalf, and Kieran Sharp, in their book “Paving Our Ways: A History of the World’s Roads and Pavements” write that some believe that the streets of Mesopotamia were paved with bitumen spread thin, just like our streets today.¹³

Bitumen is thick, gooey, dark black, and semi-solid. It is the same consistency as cold molasses, or peanut butter. Ancient people who used it would have collected it from seeps rising up from the ground or masses floating in the sea. Current bitumen extraction is undertaken in two ways—the highly destructive practice of open-pit surface mining and through “in-situ” extraction. Bitumen deposits that are located within 75 meters of the surface of the ground are recoverable with open-pit mining; this is approximately 20% of all bitumen deposits in the world.¹⁴ The rest is mined in-situ. Conventional oil drilling techniques are unfeasible given bitumen’s thickness and stickiness. The Athabasca tar sands in Alberta, Canada are the world’s largest known deposit of bitumen and holds an oil deposit the size of the city of New York—supplying half of the oil that flows from Canada into the US.¹⁵

THE MATERIAL PRESENT (SPACE)

Open-pit mining leaves behind an indelibly altered landscape. The bitumen sourced from open-pit mining is surface-mined—meaning that the entirety of organic material on the surface of the ground—trees, plants, the top layers of soil are carved away, leaving an open, cleared surface. The pits, when viewed from above, are intricate, their scale disoriented through strange textures and huge, abstracted shapes. Like an oil painting, bits of cadmium green cling to streaked umbers and grays. Clusters of massive hydraulic shovels and cranes are made tiny, their stillness and smallness disarming. Long lines curl across the landscape, creating shadows. These shadows are the result of horizontal cuts into the earth called “benches.” Like the terraced fields of rice farming, which turn steep slopes into thin bands of flattened productive space, the benches of open-pit mining enable access to the bitumen lying dormant in the ground. The benches allow heavy equipment to gain access to the seams of bitumen in the ground and provide a structural element to the open pit. The pit grows—sinks, deepens, gapes—as bitumen is extracted until the cost of removing, loading, and transporting rock, followed by the removal, loading, and transportation of bitumen, outweighs the profit. The industry refers to the concept of an ‘overall stripping ratio’—i.e., the average volume or mass of waste removed per unit of bitumen-rich sand extracted. As this ratio rises, the cost of extraction increases and can contribute to the moment when bitumen mining is no longer economically viable.

Open-pit mining is a dance between systems of vertical and horizontal sensing. Holes are drilled into the ground in a regular pattern in order to identify the spread of the bitumen’s underground body. The data points compose an approximation of the bitumen’s spread, from this matrix, inscribed on a map and delineates the location of the mining. The promise of the body of the bitumen, stretching underground in a series of wide horizontal seams, informs the locations for the benches, which mimic the deposits that run horizontally underground. Ramps connect the benches, creating gentle grades that allow for heavy machinery to reach the deposits with a typical hydraulic shovel load of 90 tonnes.¹⁶ Mining shovels scoop huge quantities of oil sands into trucks, which deliver the sticky mixture to a processing facility. The mined oil sands are estimated to hold between 7 to 13% bitumen by weight.¹⁷ At the processing facility, bitumen-rich tar sands are mixed with hot water, and agitated, separating the material into component parts: sand, water, and bitumen.

The water and sand are disposed of, the water that is left over sprawls out, becoming city-sized ponds of gloopy toxic waste known as tailings ponds. Meanwhile, the bitumen is thinned with a diluting chemical, usually natural gas or crude oil. This combination, now thin enough to flow through pipelines, is sent to an upgrading facility, where it is processed into a synthetic crude oil. Two tonnes of mined tar sands are required to produce one barrel of crude oil. The oil is used for a variety of things—often sent for further refinement, or used in roof membranes or other waterproofing applications, but most likely it is mixed with an aggregate and used for road cover.

To the bitumen extraction industry, the rocks and soil and plants that compose the middle space between the surface and the seams of bitumen deposit are nothing more than waste, spoil, a burden. In fact, this material is called overburden. The material between two strata of economically desirable material is called the interburden. Any overburden with bitumen content is likely used in general construction purposes such as mixing into concrete or acting as a base for roadways. Overburden lacking bitumen content is used to remediate and reclaim the area from which it was removed—like deviled eggs, when the yolk is removed, jumbled up, and returned. Oil companies in charge of extraction are also in charge of restoring the landscape, a slippery term given the lack of clarity over what, exactly, it means to “restore” a landscape. During the mining process, when the pit exists and requires an absence, the overburden might be dumped nearby, creating a kind of inversion of the pit; a hill that grows because of the absence of ground. Or the overburden might be taken to a third location, and placed in storage until the moment that the overall stripping ratio is met and the stripping cannot be justified anymore when finally, the pit is filled back in, and deemed, ‘restored’.

The alternative to this extractive practice is ostensibly less environmentally cataclysmic. In-situ mining involves the injection of high-pressure steam into long, deep-reaching pipes known as boreholes. The steam is pushed 500 feet underground, where it flows through millions of slits in a steel borehole liner and liquifies all bitumen within 160 feet of it.¹⁸ The melted bitumen drips down, deep inside of the earth, and collects in a lower well, where it is then pumped back up to the surface and collected. The boreholes operate in large L-shapes into the earth, boring down—through overburden, Wabiskaw shales, Clearwater caprock, and into the McMurray Formation containing the bitumen reservoir), and then across, moving in a rigid formation of vertical then horizontal. Steam extraction leaves a much smaller footprint on the land and requires less money to be spent on earth moving, earth storing, earth remediating, while enabling extractors to reach bitumen located up to half a kilometer underground.¹⁹ In-situ mining requires 90% less land intervention than open-pit mining and can access bitumen reserves deeper than 75 meters.²⁰ However, the process is highly energy-intensive, requiring large amounts of natural gas to heat the water into steam.

Freshwater is an integral aspect of the bitumen extraction process. In the Athabasca tar sands in Alberta, Canada, water usage has been at the core of numerous struggles between environmental groups, Indigenous groups, the government, and mining companies. The tar sands are located in the Peace-Athabasca delta which is one of the world’s largest freshwater deltas. The free-flowing Athabasca river runs through it, originating in the Columbia Icefields in Alberta’s Jasper National Park and flowing more than 765 miles into Lake Athabasca on the Saskatchewan and Alberta border. The provincial government of Alberta has allocated 8% of the total Athabasca River water flow to the Oil Sands facilities, which is just shy of the allocation of water (11%) for municipal needs.²¹ In 2011, mining companies siphoned approximately 370 million cubic meters of water from the Athabasca River, which was greater than the supply used by the entire city of Toronto and more than twice the municipal water needs of the City of Calgary.²² These tar sands mining companies pay nothing for the water.²³

The actual amount of water withdrawn from the Athabasca River varies year-to-year; this is the result of the changing need for water depending on the type of extraction, with in-situ extraction requiring far less freshwater—the changing amount of oil produced, and the changing flow of a seasonally influenced, un-dammed, free flowing river. Steven Wallace, the head of Alberta’s groundwater management unit, claims that industries withdraw only 1% of river flow which is compared to the 8% of flow they are allocated.²⁴ However, during periods of low flow, including in the winter, when the majority of the river freezes, or during periods of drought this can increase to as much as 25% of the Athabasca’s flow. In 2021, 968 million cubic meters (m³) of water was used in the production of 646 million barrels of oil.²⁵ Of that 968 million cubic meters, just under 200 million cubic meters was freshwater sourced from the Athabasca, either in the form of river water, groundwater, or surface runoff which the industry refers to as “makeup water.”²⁶ The remaining 770 million cubic meters is “recycled water,” which is water that has been used at least once before in the bitumen production process, and which is stored in tailings ponds.²⁷ Water in tailing ponds contains thousands of different naphthenic acids and other organic compounds, including sand, clay, and residual bitumen. These tailing ponds spread out across the landscape and are held in more than thirty man-made lakes that hold decades worth of toxic waste. The extent of these tailings ponds is profound in scale—a sea of sludge. On the land just adjacent to the oil sands mines in Northern Alberta there is over 1.4 trillion liters of waste water.²⁸ Kyle Bakx writing for the Canadian Broadcasting Corporation explained the scale of tailings ponds like this: it is the equivalent of 560,000 Olympic-sized swimming pools which would, if placed end-to-end, stretch from the city of Edmonton, Canada to Melbourne, Australia, and back again.²⁹

The effect of the tar sands mining companies’ water usage is significant. Twin satellites operated by NASA and the German Aerospace Center produced sensing data that showed a depletion of water reserves in the tar sands region and in the area just downstream—a level of water loss that may also be attributed to climate change induced changes in groundwater reserves, as well as post-glacial rebound.³⁰ Beyond the loss of water volume, the potential for pollution from the “recycled” water is calamitous. An internal government memo prepared for Canada’s Natural Resources Minister in June of 2012 outlines the concerns of geoscientists who found, “potentially harmful, mining-related organic acid contaminants in the groundwater outside of a long-established... tailings pond.”³¹ Local Indigenous groups have raised concerns for years over the contamination of oil sands-related development, including the contamination by tailings ponds of land and drinking water.³² Research conducted in the region has found elevated levels of heavy metals, including mercury and arsenic, in animals that are hunted and consumed in the region, as well as increased cancer rates in  communities like Fort Chipewyan, on the western tip of Lake Athabasca.³³

Leakage of tailings ponds into freshwater sources is becoming more and more likely. The Athabasca Chipewyan First Nation in Alberta was alerted in early 2023 to a seepage of toxic wastewater from a tailings pond at the Kearl Oil Sands mine. The leak was first detected in May of 2022, but the community was only informed that the tailings had seeped into the water in February of 2023—after a second leak of 5,300 cubic meters of sludge.³⁴ The current system relies on the industry to self-monitor any potential environmental effect; minimal enforcement enables mining companies to act in self-interest. The required remediation of the landscape does not have an enforceable timeline and an internal estimate by the Alberta Energy Regulation states that oil sands remediation could cost upwards of $95 billion USD with the official estimate resting at only $27 billion US dollars.³⁵ The current amount held in the oil sands mine clean-up fund, as of 2022, is $665 million US dollars—a gap almost comically large, if it wasn’t so disturbing.³⁶

Disturbing it is—a situation in which the extraction of material from origin site to building site radically and massively alters an entire terrain. The image that is conjured by such massive displacement of material and development into the earth is that of the mine and the skyscraper: the image of the extraction pit a “city turned upside down” as art historian Lucy Lippard writes in her book Undermining.³⁷ Yet in the case of asphalt, the inversion is not so calculated, there is something messier occurring. The extreme horizontality and flatness of asphalt as an applied surfacing material, and the depths that the extraction process undergoes to access the asphalt—suggests an asymmetry, Lippard’s city turned sideways.

THE DUBIOUS FUTURE (TIME + SPACE)

The asphalt that once covered the cobblestones on my West Philadelphia street is seemingly traceable—it may have come from the vast, Suman Gashi-like landscape of the Athabasca tar sands, or the sun beaten Uinta basin. It signals an experiential connection to the Babylonians, the ancient Greeks, the Nabataean seamen, and to the roads of Bogazkale and Babylon and to the Street On Which No Enemy May Ever Tread. But, I wonder what my new-found understanding of asphalt’s material history does for me. Does it, as Pallasmaa writes, allow me to settle myself into the world, to insert myself into the continuum of culture and time?³⁸

I think it does. There is an undeniable relief in the fact that asphalt—a material I will have been surrounded by in almost every city I’ve visited, every sidewalk I’ve walked on, every road trip—has some semblance of human history, an ancientness that, like brick or wood or stone, allows for the satisfaction of a shared lineage. I, too, stand on roads paved with bitumen! I imagine explaining to an ancient Greek time traveller as I walk down the street, luxuriating for a few seconds in associations that tie me to other times, other places. I think too of the smell of rain on asphalt, the rich dark beauty of freshly poured asphalt, summer highway drives, and the sensorial placing of asphalt acting as material witness to so many other memories.

But overwhelming the sense of relief is one of disgust. The knowledge of the extraction method implicates me in the sinister, distorted reality of our dependence on petrochemicals. For every second of historical relief there are hours of icy chill, the fever vision of 560,000 Olympic-sized swimming pools of toxic sludge, of deviled egg overburden lumped in flaccid hills, of scraping, of oily scum, of barren cuts. I am settled, uncomfortably, into the world through this material knowledge. Both I and the street outside are placed into a continuum of culture and time, one that reminds me of the inescapable destruction that our modern age has brought. Lucy Lippard writes that the great pits of extractive mining, “transform the geological past into dubious futures.” I imagine our extraction of asphalt as just that, a road connecting past to present to dubious, destructive future.