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Aral Sea Disiccation Linked to Deep Earth Changes
The drastic shrinking of the Aral Sea, a consequence of decades of unsustainable irrigation practices and persistent drought conditions, has had profound environmental repercussions, extending far beneath the Earth’s surface, impacting even the upper mantle. This represents a potentially unprecedented example of human-induced alterations reaching deep within the solid Earth.
Human Activity’s Impact on Earth’s Mantle
“The notion that human actions can influence the upper mantle is truly remarkable,” notes Sylvain Barbot of the University of Southern California. “It underscores the immense capacity we possess to modify our planet’s environment.”
The Aral Sea’s Demise: From Giant Lake to Desert
Once considered one of the world’s largest inland water bodies, the Aral Sea, situated in Central Asia, spanned nearly 70,000 square kilometers. However, commencing in the 1960s, Soviet-era irrigation projects, compounded by recurring dry spells, precipitated the sea’s rapid depletion. By 2018, its volume had contracted by approximately 90 percent, translating to a loss of roughly 1000 cubic kilometers of water.
Scientific Inquiry into Deep Earth Response
Wang Teng, a researcher at Peking University in China, was motivated to investigate the Aral Sea’s situation after studying the environmental disaster’s surface-level effects. “I realised that such a considerable alteration in mass could trigger reactions deep within the Earth,” he explained.
Measuring Surface Uplift via Satellite Technology
Utilizing satellite data, Wang and his colleagues, including Barbot, meticulously monitored minute shifts in the dried seabed’s elevation between 2016 and 2020. Despite the majority of the water disappearing decades prior, their analysis revealed ongoing surface uplift, averaging about 7 millimeters annually.
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Crust and Mantle Modeling Confirms Deep Earth Reaction
To ascertain the subsurface mechanisms behind this uplift, the research team employed a model simulating the crust and mantle beneath the Aral Sea. “Our findings indicate that the observed uplift is entirely consistent with a deep-seated response to the water loss,” Barbot stated.
Mantle Viscosity and Delayed Uplift Phenomenon
According to their model, the Earth’s crust, being more readily deformable, reacted initially to the reduced water weight by flexing upwards. This crustal unbending then initiated a reaction as deep as 190 kilometers, prompting viscous mantle rock within the upper mantle to gradually flow into the newly created space. “The upward flexing creates space, and the subsurface rocks tend to migrate into it,” Barbot elaborated. This delayed mantle response, occurring in a heat-sensitive, weaker mantle region termed the asthenosphere, explains the continued uplift even years after the sea’s desiccation.
Aral Sea Impact Compared to Glacial Rebound
Roland Bürgmann, a researcher at the University of California, Berkeley, acknowledges that mantle rebound is a known post-glacial phenomenon. However, he suggests that the Aral Sea drainage might represent the most extreme case of human-induced deep Earth changes in solid rock observed thus far.
Broader Implications of Human-Induced Earth Changes
Manoochehr Shirzaei of Virginia Tech points out other human activities, such as creating large artificial lakes and extracting groundwater, also induce crustal rebound. Yet, the vast geographical scale of the Aral Sea basin suggests its desiccation is likely to have caused deeper and more extensive effects.
Opportunity to Study Mantle Behavior
Beyond highlighting the magnitude of human influence, the observed uplift beneath the Aral Sea provides a unique chance to assess subtle variations in mantle viscosity, particularly beneath continental interiors, according to Bürgmann. “Understanding the behavior of this sub-continental mantle layer is crucial for researchers studying plate tectonics.”