Tag: Waste disposal

Human interventions in geological processes

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During the Industrial Revolution not only did the emission of greenhouse gases by burning fossil fuels start to increase exponentially, but so too did the movement of rock and sediment to get at those fuels and other commodities demanded by industrial capital. In the 21st century about 57 billion tons of geological materials are deliberately moved each year. Global population followed the same trend, resulting in increasing expansion of agriculture to produce food. Stripped of its natural cover on every continent soil began to erode at exponential rates too. The magnitude of human intervention in natural geological cycles has become stupendous, soil erosion now shifting on a global scale about 75 billion tons of sediment, more than three times the estimated natural rate of surface erosion. Industrial capital together with society as a whole also creates and dumps rapidly growing amounts of solid waste of non-geological provenance. The Geological Society of America’s journal Geology recently published two research papers that document how capital is transforming the Earth.

Dust Bowl conditions on the Minnesota prairies during the 1930s.

One of the studies is based on sediment records in the catchment of a tributary of the upper Mississippi River. The area is surrounded by prairie given over mainly to wheat production since the mid 19th century. The deep soil of the once seemingly limitless grassland developed by the prairie ecosystem is ideal for cereal production. In the first third of the 20th century the area experienced a burst of erosion of the fertile soil that resulted from the replacement of the deep root systems of prairie grasses by shallow rooted wheat. The soil had formed from the glacial till deposited by the Laurentide ice sheet than blanketed North America as far south as New York and Chicago. Having moved debris across almost 2000 km of low ground, the till is dominated by clay- and silt-sized particles. Once exposed its sediments moved easily in the wind. Minnesota was badly affected by the ‘Dust Bowl’ conditions of the 1930s, to the extent that whole towns were buried by up to 4.5 metres of aeolian sediment. For the first time the magnitude of soil erosion compared with natural rates has been assessed precisely by dating layers of alluvium deposited in river terraces of one of the Mississippi’s tributaries  (Penprase, S.B. et al. 2025. Plow versus Ice Age: Erosion rate variability from glacial–interglacial climate change is an order of magnitude lower than agricultural erosion in the Upper Mississippi River Valley, USA. Geology, v. 53, p. 535-539; DOI: 10.1130/G52585.1).

Shanti Penprase of the University of Minnesota and her colleagues were able to date the last time sediment layers at different depths in terraces were exposed to sunlight and cosmic rays, by analysing optically stimulated luminescence (OSL) and cosmogenic 10Be content of quartz grains from the alluvium. The data span the period since the Last Glacial Maximum 20 thousand years ago during which the ecosystem evolved from bare tundra through re-vegetation to pre-settlement prairie. They show that post-glacial natural erosion had proceeded at around 0.05 mm yr-1 from a maximum of 0.07 when the Laurentide Ice Sheet was at its maximum extent. Other studies have revealed that after the area was largely given over to cereal production in the 19th century erosion rates leapt to as high as 3.5 mm yr-1 with a median rate of 0.6 mm yr-1, 10 to 12 times that of post-glacial times. It was the plough and single-crop farming introduced by non-indigenous settlers that accelerated erosion. Surprisingly, advances in prairie agriculture since the Dust Bowl have not resulted in any decrease in soil erosion rates, although wind erosion is now insignificant. The US Department of Agriculture considers the loss of one millimetre per year to be ‘tolerable’: 14 times higher than the highest natural rate in glacial times.

The other paper has a different focus: how human activities may form solid rock. The world over, a convenient means of disposing of unwanted material in coastal areas is simply to dump waste in the sea. That has been happening for centuries, but as for all other forms of anthropogenic waste disposal the volumes have increased at an exponential rate. The coast of County Durham in Britain began to experience marine waste disposal when deep mines were driven into Carboniferous Coal Measures hidden by the barren Permian strata that rest unconformably upon them. Many mines extended eastwards beneath the North Sea, so it was convenient to dump 1.5 million tons of waste rock annually at the seaside. The 1971 gangster film Get Carter starring Michael Caine includes a sequence showing ‘spoil’ pouring onto the beach below Blackhall colliery, burying the corpse of Carter’s rival. The nightmarish, 20 km stretch of grossly polluted beach between Sunderland and Hartlepool also provided a backdrop for Alien 3. Historically, tidal and wave action concentrated the low-density coal in the waste at the high-water mark, to create a free resource for locals in the form of ‘sea coal’ as portrayed in Tom Scott Robson’s 1966 documentary Low Water. Closure of the entire Duham coalfield in the 1980s and ‘90s halted this pollution and the coast is somewhat restored – at a coast of around £10 million.

‘Anthropoclastic’ conglomerate formed from iron-smelting slag dumped on the West Cumbrian coast. It incorporates artefacts as young as the 1980s, showing that it was lithified rapidly. Credit: Owen et al, Supplementary Figure 2

On the West Cumbrian coast of Britain another industry dumped millions of tons of waste into the sea. In the case it was semi-molten ‘slag’ from iron-smelting blast furnaces poured continuously for 130 years until steel-making ended in the 1980s. Coastal erosion has broken up and spread an estimated 27 million cubic metres of slag along a 2 km stretch of beach. Astonishingly this debris has turned into a stratum of anthropogenic conglomerate sufficiently well-bonded to resist storms (Owen, A., MacDonald, J.M. & Brown, D.J 2025. Evidence for a rapid anthropoclastic rock cycle. Geology, v. 53, p. 581–586; DOI: 10.1130/G52895.1). The conglomerate is said by the authors to be a product of ‘anthropoclastic’ processes. Its cementation involves minerals such as goethite, calcite and brucite. Because the conglomerate contains car tyres, metal trouser zips, aluminium ring-pulls from beer cans and even coins lithification has been extremely rapid. One ring-pull has a design that was not used in cans until 1989, so lithification continued in the last 35 years.

Furnace slag ‘floats’ on top of smelted iron and incorporates quartz, clays and other mineral grains in iron ore into anhydrous calcium- and magnesium-rich aluminosilicates. This purification is achieved deliberately by including limestone as a fluxing agent in the furnace feed. The high temperature reactions are similar to those that produce aluminosilicates when cement is manufactured. Like them, slag breaks down in the presence of water to recrystallis in hydrated form to bond the conglomerate. This is much the same manner as concrete ‘sets’ over a few days and weeks to bind together aggregate. There is vastly more ‘anthropoclastic’ rock in concrete buildings and other modern infrastructure. Another example is tarmac that coats millions of kilometres of highway.

See also: Howell, E. 2025. Modern farming has carved away earth faster than during the ice age. Science, v. 388

Sedimentary deposits of the ‘Anthropocene’

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Economic activity since the Industrial Revolution has dug up rock – ores, aggregate, building materials and coal. Holes in the ground are a signature of late-Modern humanity, even the 18th century borrow pits along the rural, single-track road that passes the hamlet where I live. Construction of every canal, railway, road, housing development, industrial estate and land reclaimed from swamps and sea during the last two and a half centuries involved earth and rock being pushed around to level their routes and sites. The world’s biggest machine, aside from CERN’s Large Hadron Collider near Geneva, is Hitachi’s Bertha the tunnel borer (33,000 t) currently driving tunnels for Seattle’s underground rapid transit system. But the record muck shifter is the 14,200 t MAN TAKRAF RB293 capable of moving about 220,000 t of sediment per day, currently in a German lignite mine. The scale of humans as geological agents has grown exponentially. We produce sedimentary sequences, but ones with structures that are very different from those in natural strata. In Britain alone the accumulation of excavated and shifted material has an estimated volume six times that of our largest natural feature, Ben Nevis in NW Scotland. On a global scale 57 billion t of rock and soil is moved annually, compared with the 22 billion t transported by all the world’s rivers. Humans have certainly left their mark in the geological record, even if we manage to reverse  terrestrial rapacity and stave off the social and natural collapse that now pose a major threat to our home planet.

A self propelled MAN TAKRAF bucketwheel excavator (Bagger 293) crossing a road in Germany to get from one lignite mine to another. (Credit: u/loerez, Reddit)

The holes in the ground have become a major physical resource, generating substantial profit for their owners from their infilling with waste of all kinds, dominated by domestic refuse. Unsurprisingly, large holes have become a dwindling resource in the same manner as metal ores. Yet these stupendous dumps contain a great deal of metals and other potentially useful material awaiting recovery in the eventuality that doing so would yield a profit, which presently seems a remote prospect. Such infill also poses environmental threats simply from its composition which is totally alien compared with common rock and sediment. Three types of infill common in the Netherlands, of which everyone is aware, have recently been assessed (Dijkstra, J.J. et al. 2019. The geological significance of novel anthropogenic materials: Deposits of industrial waste and by-products. Anthropocene, v. 28, Article 100229; DOI: 10.1016/j.ancene.2019.100229). These are: ash from the incineration of household waste; slags from metal smelting; builders’ waste. What unites them, aside from their sheer mass, is the fact that are each products of high-temperature conditions: anthropogenic metamorphic rocks, if you like. That makes them thermodynamically unstable under surface conditions, so they are likely to weather quickly if they are exposed at the surface or in contact with groundwater. And that poses threats of pollution of soil-, surface- and groundwater

All are highly alkaline, so they change environmental pH. Ash from waste incineration is akin to volcanic ash in that it contains a high proportion of complex glasses, which easily break down to clays and soluble products. Curiously, old dumps of ash often contain horizons of iron oxides and hydroxides, similar to the ‘iron pans’ in peaty soils. They form at contacts between oxidising and reducing conditions, such as the water table or at the interface with natural soils and rocks. Soluble salts of a variety of trace elements may accumulate, such copper, antimony and molybdenum. Slags not only contain anhydrous silicates rich in the metals of interest and other trace metals, which on weathering may yield soluble chromium and vanadium, but they also have high levels of calcium-rich compounds from the limestone flux used in smelting, i.e. agents able to create high alkalinity. Portland cement, perhaps the most common material in builders’ waste, is dominated by hydrated calcium-aluminium silicates that break-down if the concrete is crushed, again with highly alkaline products. Another component in demolition debris is gypsum from plaster, which can be a source of highly toxic hydrogen sulfide gas generated in anaerobic conditions by sulfate-sulfide reducing bacteria.