Next to the main airport in Mexico City, a curious leftover triangle that has been transformed into a park, houses an invisible landscape. Under Alameda de Oriente’s trees, ponds, and grasses, sits rubble from one of the city’s largest disasters, the 1985 earthquake.

In every construction process, there is waste, and when the process is deconstruction or demolition, that waste is exponential. All this waste will inevitably end up in our soil. Our current culture of “sustainability” in architecture tends to focus on new ways to recycle and reuse efficiently. What if we push this a step further and think about construction systems that improve soils? What if we design our waste to make more fertile soils?

On the morning of 19 September 1985, an 8.2 magnitude earthquake on the Richter scale violently shook every corner of the Federal District. The streets turned into corridors filled with lime and debris from the nearly 300 buildings that collapsed. From hotels to schools, countless structures were damaged. This earthquake radically changed the face of Mexico City.

At the former site of Laguna de Xochiaca (now Alameda de Oriente park), an extension of one of Mexico City’s largest landfills known as Bordo de Poniente, the changes to the landscape had little to do with the city’s skyline—it has been invisible to most of its citizens. The impact of the earthquake only became crucial for a few thousand pepenadores¹ who started their new life on top of 1.6 million cubic metres of rubble and debris deposited over the following two years.

Consisting mostly of concrete, red brick, and asphalt, the rubble was compacted with heavy machinery to a thickness of between 2.5 and 3 metres. After the massive pile started being deposited, plans for a park began almost immediately. By late 1988, construction had begun. The first step was to forcibly relocate the pepenadores, and the second step was to cap the entire site with about 20 centimetres of “tepetate.” Tepetate is a kind of highly weathered clay material typically produced in the region by lahar deposits and can be used to form adobe bricks. It is extremely infertile as soil but is readily available from nearby or can be excavated from major construction sites within the city, such as the Metro tunnels, deep drainage holes, or the foundations of multistory buildings. Finally, a thin layer of topsoil was added. This was not really enough to keep vegetation alive, so after the opening of the largest composting plant in the city in 2004, compost layers of about 30 centimetres were added regularly to some parts of the park.

In September 2015, there was a moment of revelation. As part of the SUITMA (Soils of Urban, Industrial, Traffic, and Mining Areas) 8 Soil Science Conference in Mexico City, organizers from the Universidad Nacional Autónoma de México brought a large number of urban soil scientists to see the result of the experiment. They dug a 2-metre by 1-metre hole on the centre island of the Alameda main pond and were astonished to discover that the pile of rubble and construction debris from thirty years ago was actually the beginning of the formation of a “technosol”—a type of soil defined by a mix of pieces of artifacts of anthropogenic origin.²

As landscape architects, we think we need the best conditions for our landscapes to be designed. But in fact, the sites that still remain (and will become available) in our cities will never be perfect or pristine with incredibly fertile soil. It is more important to be able to revive, transform, and bring back to life all those neglected sites that are often marginalized from the city. Our past urban materialities can be crushed, piled, and nourished to become new landscapes that support life.

A pile of earthquake debris and construction rubble, a thin layer of clay, and some topsoil mixed with raw compost can become fertile soil in a period of less than thirty years. We should have hope in the processes of soil formation that, though slow, are silently able to transform landscapes. In fact, this might be a regenerative way of transforming our urbanized areas. While these spaces are not going to become pristine landscapes of untouched material, they are landscapes of hope. The hope of thinking about our cities and their constant transformation.

Could we think that our cities host their past lives under our feet? How should we build our cities if we think about them as future layers of a more fertile soil profile? These questions have been rattling around in my head, and I am curious to hear what you think, Elise.