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Getting to the bottom of the Oxford sinkhole mystery

['Did You Know That with Alan Walter']
['Did You Know That with Alan Walter']

Did You Know with Alan Walter

The Carboniferous Period between 300 and 350 million years ago was a very busy time in what we now know as Cumberland County.  The earliest species of plants and animal life on the planet were flourishing here and would contribute to Joggins Fossil Cliffs’ unrivalled fossil record.

Our planet’s continents were also converging at that time to form Pangea, a single supercontinent, on which our province-to-be could be found near the equator.

However, this was no “ocean playground” - all but the highlands in Nova Scotia, and Prince Edward Island were submerged in an ancient body of sea water that was named by geologists as the Windsor Sea, after the Windsor area of our province.

Sea levels periodically rose and fell during the 15 million years that the Windsor Sea existed. Isolated bays, while periodically cut off from the sea, were regularly replenished with incoming sea water; and vast deposits of minerals such as gypsum and salt were laid down over that period through evaporation.

The Canadian Salt Co. Ltd operation in Pugwash now profits from mining such a salt deposit, large enough for the future lifespan of the mining operation to be estimated at over one hundred years; and the salt itself is appropriately branded and marketed as “Windsor Salt”.

As for the town of Oxford’s sinkhole situation, it is likely a result of this same alternating flooding and evaporation process creating deposits of gypsum beneath the town, in as yet unknown quantities.

The word gypsum is derived from the Greek word “gypsos” for "plaster”, and gypsum has many uses today in construction as a mortar and in drywall fabrication. As a mineral deposit it behaves as a soft rock that will eventually dissolve in groundwater. In Oxford a large quantity must have dissolved creating a cavity which became a large sinkhole in the Oxford Lions Park.

What happened in that park would come as no great surprise to experts in the field, since an on-line geological map of Nova Scotia clearly indicates the likelihood of gypsum deposits in the Oxford area. And gypsum sinkholes are not an uncommon occurrence in the province, although this one is already quite spectacular.

Amy Tizzard, a geologist with the Nova Scotia Department of Energy and Mines, advised that it was too early to tell how big the Oxford sinkhole will get, saying that "sinkholes are unpredictable in their nature so we can't rule anything out at this point."

She added that “we want to gather as much information as possible around the sinkhole so we’re looking at different investigative techniques that includes some high precision surveying to monitor differences in elevation and using ground-penetrating radar which can help image the sub-surface and get a better idea of the seriousness of the problem.”

The province has also asked the federal government for assistance and additional geophysical scanning equipment is being dispatched to the site.

The town of Oxford will be able to rest easier when the investigative results hopefully indicate a restricted, manageable situation; and the Lions Park facility can resume its important community role following some albeit costly reparations.

 

Alan Walter is a retired professional engineer living in Oxford. He was born in Wales and worked in Halifax. He spends much of his time in Oxford, where he operates a small farm. He can be reached at alanwalter@eastlink.ca.

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