On February 22nd, 1983, it was a quiet summer day in central Lesotho.
It was warm with a temperature of 29 degrees Celsius or 84.2 degrees fahrenheit with mostly
clear skies.
Then, unexpectedly at 6:26 pm local time, the ground began to shake.
This shaking continued for several seconds, as a magnitude 4.3 earthquake struck the region.
Initially, not much was thought of this.
Although unusual, quakes of this magnitude occur in the country about once every 9 or
10 years.
Although the quake was thought at first to have not caused any significant damage, it
was later indirectly linked to a wooden power line pole which catch on fire, which was visible
for several kilometers.
As curious people and repair crews approached the site of the fire, they found something
completely unexpected.
Emitting from the ground at a very low rate was a volume of orangish red molten rock.
This lava slowly flowed outwards from a vent in the ground, leaving behind a ropy texture
which is referred to as pahoehoe.
Although many nations within the African continent have abundant volcanoes which have produced
recent eruptions, including unexpected countries such as Libya, Lesotho is not known to have
any active volcanoes.
In fact, Lesotho is not known to have been the site of a volcanic eruption in more than
40 million years.
So, did the first volcanic eruption in Lesotho in several million years occur in 1983, or
was something else the cause?
The apparent volcanic eruption occurred in central Lesotho where it was 3.5 kilometers
east of Bushman's pass at the coordinates marked on screen.
As we zoom in on the eruption site, something immediately looks off.
Located on a hillside, you would normally expect a lava flow which erupted on such a
steep slope to have covered a significant portion of the hill in a dark black layer
of lava.
Instead, there is only a faint and small black dot on the hillside, as the eruption did not
produce a typical volume of molten rock associated with small volume basaltic eruptions.
While small volume basaltic volcanic eruptions typically produce around 10 million cubic
meters of lava, this eruption only produced a single cubic meter, and lava only travelled
3 meters or 10 feet.
This was the first sign that something was wrong, as generally speaking such a small
volume of lava in a volcanic eruption is incredibly unlikely.
Many basaltic eruptions which involve effusive lava flows tend to produce between 30 and
200 million cubic meters of material, as was the case during the 2021 eruptions of both
Geldingadalir in Iceland and La Palma in the Canary Islands.
Eventually, small segments of cooled lava were removed from the hillside in Lesotho
and taken in for analysis.
Its elemental composition was near identical to that of a rock which composes the vast
majority of the nearby landscape.
Approximately 183 million years ago, several hundred meters thick of basalt lava flooded
onto the surface in a large volume flood basalt eruption, forming in part the relevant hillside.
This suggests that rather being new lava, what erupted was merely remelted surface rock.
However, one thing was quite different between the ancient and 1983 lavas; the 1983 lavas
contained triple the amount of zinc that the older lavas did.
While this could be explained by other means, this most likely represents zinc which melted
off into the lava from a nearby stay wire on a power line.
The final nail in the coffin for the idea that an eruption did truly occur was found
when a hole was dug into the ground to take a look at the expected deeper magma conduit
which supplied material to the surface.
Instead of seeing solidified lava which went down several hundred to thousand meters below,
it only went down 2 meters after which the lava was completely absent.
What had most likely occurred was that lightning from a stray thunderstorm struck an adjacent
power line and transferred much of the energy into the stay wire which acted as a grounding
wire, which then melted a volume of surrounding host rock.
Although some people still believe to this day that Lesotho was the site of a volcanic
eruption in 1983, a near identical incident occurred at Tor Zawar in Pakistan in 2010
which also created lava connected to a grounded power line wire.
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