Pele's Hair is a natural spun glass formed by blowing-out during quiet fountaining of fluid lava, cascading lava falls, or turbulent flows, sometimes in association with pele tears. Pele's hair, named after the volcanic deity Pele.
During vigorous gas-driven eruption of basaltic lava, a variety of pyroclastic materials may form, in including fine strands of brown sideromelane glass known as Pele's hair. Relatively little Pele's hair forms compared with the bulkier pyroclastic products, and much of this hair is quickly dispersed downwind during eruption.
Masses of hair may collect around active vents, but these commonly are quickly covered by subsequent flows that may remelt the glass strands. Thus, there is little chance for the preservation of sizeable deposits of Pele's hair; such samples must be collected at the time of hair formation or shortly thereafter.
|Pele's Hair and Pele's Tears from Hawaii|
Left Photo: Ivtorov, Right Photo: National Park Service
Pele's hair forms from droplets that are stretched into threads. Typically, Pele's hair is roughly circular in cross section with a diameter between about 1 and 300 micrometres. In detail, the basic cylindrical form exhibits numerous modifications, including bent, bifurcated, and pretzellike shapes, and changes in diameter as much as an order of magnitude either abruptly over lumps caused by microphenocrysts and vesicles or gradually from one end of a strand to another.
The interiors of hairs are also varied. Solid glass cylinders occur, but spherical to elongate vesicles are common. Elongate vesicles form capillary-like tubes parallel to hair axes and occur both singly and multiply, commonly producing a thin-walled tube or bundle of tubes. Strands of Pele's hair may be up to a couple feet long, but only one micron (.001 mm) thick.
Because these strands are so light, they can become airborne and be carried by the wind. They may accumulate in low-lying areas and form dense mats many inches deep. While fragile and brittle, they are also sharp. As tiny pieces of glass, they can become lodged in human skin and much worse, eyes. Caution around the fibers is necessary to avoid injury from the slivers.
|Pele's hair that came from lava within Kilauea volcano, in Hawaii Volcanoes National Park. |
(Image credit: Alamy)
Pele's tears are small spherical pyroclasts. Their sizes are variable (from few μm to several hundreds μm of diameter) and their surfaces are generally rough. Pele's tears are commonly observed on the walls of Pele's hairs and also within cavities of Pele's hairs. This would suggest they formed prior to being trapped within the strand and supports a different mechanism for formation. It has been considered that they became trapped during transport in the eruptive plume.
|Pele's tear with two attached threads of Pele's hair, Kilauea Volcano, Hawaii|
Photo: James St. John
Pele's tears are oftentimes found attached to a strand of Pele's hair, and Pele's tears and hairs are usually sampled together after an eruptive event. Pele's hairs are a widely distributed clast morphology in sub marine environments. However, Pele's hairs and tears are most typically associated with small subaerial explosive eruptions of low-viscosity basaltic melts.
In many cases, Pele's hairs and tears are formed by deformation of low-viscosity lava in the air. In low viscosity magmas, droplet shape is controlled by surface tension, acceleration of the droplet after eruption and air friction.
The formation of these tears is a complex process depending on a number of different factors as a tiny droplet of lava is being erupted from a lava fountain. Whilst it is travelling through the air two things are happening: it is cooling down very rapidly (a process known as quenching) and it is being deformed. The deformation of a droplet depends on the speed at which it is erupted from the volcano, its surface tension, the viscosity (thickness) of the magma and the resistance it experiences as it travels through the air.
Pele's tears, like Pele's hair, are named after Pele, the Hawaiian fire goddess of volcanoes.
See also: Rainbow Obsidian