Despite humans making up only about 0.01% of Earth’s history, our impact on natural landscapes and long-standing processes has been profound and rapid. A recent study by researchers from the University of Glasgow examines the transformation of Britain’s sandy beaches, shedding light on these swift changes.

From 1856 until the 1980s, industrial steel and iron furnaces operated widely in Britain, resulting in the disposal of approximately 335 million cubic meters (90 billion gallons) of molten furnace waste. Slag waste has accumulated nationwide, with about 27 million cubic meters (6 million gallons) forming a towering 30-meter (100-foot) cliff at Derwent Howe.

The research focused on understanding how these hillside formations are created, particularly the influence of artificial materials on rock formation. Rocks undergo a natural transformation process over millions of years through lithification in the rock cycle. The discovery of a soda can tab from 1989 within the hardened grain of slag led the team to conclude that the beach had solidified in the last 35 years, prompting them to introduce a new term for rocks formed from human deposits: the human crushing cycle.

The researchers collected 1,300 sediment grains from 13 sites and discovered that a remarkable 83% comprised slag. In contrast, natural beach materials like silica sand constituted only 17% of the samples. Waves and winds eroded the cliffs, releasing chunks of slag, which were then carried to the beach.

Moreover, they noted the slag’s penetration into the wet sediments where it met the shoreline. The formed rocks bore resemblance to peperite, typically produced when lava overlays wet sediment. This unique interaction resulted in a rock appearance resembling a chunk of slag encased in sandstone.

Utilizing sedimentary analysis, the researchers studied how slag particle arrangements within the solidified rock reflected tidal water speeds at various historical intervals. These arrangements, known as sediment structures, indicate the methods of rock formation. For example, water flowing over sand may create rippled patterns that become preserved when the sand hardens into rock.

As water speeds increase, ripple formations disappear, giving way to horizontal sediment layers, known as flat layers. The researchers identified both trough cross-bedding and planar bedding within the Slugby Beach rocks, indicating that Derwent Howe’s beach transitioned from loose sediment to solid rock in just one generation.

To uncover the reason behind this rapid solidification, the research team employed a scanning electron microscope (SEM) coupled with energy-dispersive X-rays (EDX). By analyzing the rocky surface with electron beams and X-rays, they identified key binder minerals—calcium- and iron-rich compounds such as calcite, goethite, and brucite. These minerals serve as cement to bind sediment particles together.

The researchers anticipated that the slag would lead to these cement compositions due to the high solubility of calcium, magnesium, manganese, and iron from metal ore extraction. As water flowing between the slag particles becomes saturated with dissolved elements, this leads to the rapid formation of solid mineral cement in environments where high concentrations exist.

The implications of their findings suggest that the anthropogenic rock cycles observed at Derwent Howe may not be unique. Given that slag contains elements necessary for rock formation, similar deposits around the world could significantly affect local environments. Consequently, the research team recommends updating geological models to better reflect human influences on natural rock cycles.

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