The Kilauea volcano in Hawaii has been near continuously erupting since 1983, albeit with
two brief pauses.
Although its summit lava lake is spectacular, there is a peculiar geologic oddity located
to its southwest.
Within the Kaʻū desert are large masses of sparkling golden strands of material.
These strands are lightweight, and since they are relatively easily blown by wind, they
can form masses which are several inches in height, sometimes completely covering an adjacent
slope sort of like a golden snow.
Despite looking like hair or animal fur, this is instead a highly unusual volcanic rock.
Specifically, it is a variety of volcanic glass which is referred to as Pele's hair.
The abundances of pele's hair in Ka'u desert are unusually high but it is not the only
location with an abundance of this fascinating rock type.
Pele's hair is also found at Masaya in Nicaragua, Erta Ale in Ethiopia, Bárðarbunga in Iceland,
and a few other volcanoes.
A closely related volcanic rock to Pele's hair which is also a type of volcanic glass
is known as obsidian.
However, there are a number of differences between the two rock types.
Although obsidian can form from numerous types of lava flows, it most frequently forms during
volcanic eruptions which produce unusually viscous high silica content lava known as
rhyolite.
For example, the Newberry volcano in oregon produced millions of tons of obsidian during
a highly explosive rhyolite composition eruption approximately 1,300 years ago.
The black volcanic glass shown in this photo cooled almost instantaneously so that definable
crystals did not develop.
Pieces of obsidian can be fairly large, as I have personally seen individual stones larger
than 2 meters or 6 feet wide.
In contrast, pele's hair tends to form at basalt composition eruptions from lava which
has a low viscosity.
While also a type of volcanic glass, it tends to have a golden color with a faint green
tint.
Pieces of pele's hair can widely vary in length, often measuring between 1 and 120 centimeters
in length.
However, strands of this glass are incredibly thin, measuring a mere 0.001 to 0.3 millimeters
wide.
This is quite comparable to the width of a strand of human hair.
So, how does Pele's hair form?
During a basaltic eruption, pele's hair can form at three separate locations.
It can form at a lava fountain, at a highly turbulent and fast moving lava flow, or a
lavafall which is also known as a "lava cascade".
All three of these settings have a few things in common; they represent locations where
lava can be ejected upwards or outwards to various extents, are areas where wind could
easily blow lightweight material away, and are settings where liquid lava can be greatly
stretched.
During the 2021 eruption in Iceland of Geldingadalir, and the adjacent 2022 eruption of Meradalir,
pele's hair was primarily created at the erupting spatter cones.
As magma is carried to the surface, volcanic gasses come with it, forming bubbles in the
material.
These bubbles eventually burst, stretching the edge of the bubble into a very thin and
long strand of material.
This material might be then carried upwards by vigorous lava fountains and subsequently
blown several hundred meters distant.
Pele's hair can also form in turbulent lava flows, as certain abrupt changes in direction
can greatly stretch cooling pieces of liquid and turn it into thin strands.
A similar abrupt vertical change in direction also occurs at lava cascades can also greatly
stretch lava bubbles and thin lava fragments into even thinner pieces, becoming pele's
hair.
Although pele's hair is fascinating to look at, I would not recommend touching it.
The golden volcanic glass is incredibly fragile and upon touching it is quite likely to burst
into thousands of pieces which would then become incredibly annoying to remove from
skin.
As a final note, pele's hair is not the only type of weird volcanic glass which basaltic
volcanoes can create.
Two similar types of glass are so called "pele's seaweed" and "pele's tears".
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