KILAUEA VOLCANO
(MT. KILAUEA)
Mt. Kilauea is the world's most active volcano.
It sits atop the Hawaii Hotspot in the central Pacific Ocean, and has been
erupting continuously since 1983. Kilauea lavas are basaltic in
composition, but the physical appearance of Kilauea's output varies
tremendously. Many of Kilauea's ongoing basaltic eruptions have occurred
along its East Rift Zone, a fracture system extending ~eastward from the
vent area.
LAVA TOE FROM KUPAIANAHA
The rock shown below shows the cross-section interior
of a lava toe (see
example in the field). Lava toes are bulbous, elongated features
formed at the distal ends of low-viscosity basaltic lava flows. This
sample was part of a lava flow covering a road in the town of Kalapana (outside
the national park), at the southeastern margin of Hawaii. The lava flow
came from the Kupaianaha eruptive center along Kilauea's East Rift Zone in the
early 1990s. Note that the interior of the lava toe is a dark
gray-colored vesicular basalt. Note also the black-colored rim, which
cooled more quickly than the interior. This black rim is mafic
obsidian (a.k.a. basalt glass; a.k.a. tachylite). Mafic
obsidian has the same physical characteristics expected for the common felsic
variety of obsidian - it has a glassy texture, with conchoidal fracture, sharp
broken edges, and a jet black color.
Lava toe
cross-section (~7.5 cm across at its widest), showing core of vesicular basalt
and rim of mafic obsidian (basalt glass; tachylite). From an early 1990s
pahoehoe lava flow erupted from Kupaianaha, East Rift Zone, Kilauea Volcano,
southeastern Hawaii.
PAHOEHOE LAVA
FROM MAUNA IKI
CRATER
Basalt lava flows in Hawaii have two types of surface
morphologies: 1) aa lava and 2) pahoehoe lava. The Hawaiian
names for these lava flow surfaces have become technical names in
volcanology. Pahoehoe lava (pronounced "pa-hoy-hoy") has a
smooth or ropy top surface. Pahoehoe surface morphologies are not
restricted to lava flows at the Hawaii Hotspot. It's commonly seen in
many basaltic lava fields on Earth.
Pahoehoe lava from Mauna Iki Crater, Kilauea Volcano, Hawaii Hotspot. (CMNH
12388, Cleveland Museum of Natural History, Cleveland, Ohio, USA)
LAVA TUBE CEILING FROM MAUNA ULU ERUPTION
Sideromelane & Tachylite (above & below; above: field of view ~9.3
cm across; below: field of view ~3.2 cm across) - exterior surface of a
lava tube ceiling sample. The surface has abundant, consolidated basalt
glass filaments, formed by stretching.
In cross-section view (see below), the rock is seen to be a highly
vesiculated basaltic glass. The rich
golden brown-colored basaltic glass is called sideromelane. The blackish-colored basaltic glass is called
tachylite.
This rock formed the thin ceiling of a lava tube that
was active during the 1969 to 1974 eruption of the Mauna Ulu Vent. The Mauna Ulu Lava Field is located along
Kilauea’s East Rift Zone. This lava tube
ceiling sample ranges from 1 to 3.5 cm thick.
Tachylite (above & below; above: field of view ~8.6 cm; below:
field of view ~4.2 cm) - interior surface of lava tube ceiling sample.
Unlike the external surface, the inside roof of the lava tube doesn't display
stretched textures. The heat inside the lava tube was sufficient to
partially re-melt already solidified lava. This surface is relatively
smooth and lustrous, somewhat like chocolate cake batter.
Vesiculated tachylite (field of view ~4.0 cm across) - the lithology of
this lava tube ceiling sample is best revealed on the broken edges. This
cross-section view shows the the rock cooled very quickly - the material itself
is glassy, with very few to no crystals, but with abundant preserved gas
bubbles (vesicles). The lithology is a
vesiculated tachylite, in other words, a black, frothy-textured, basalt glass.
KAPOHO FLOW LAVA
Vesicular porphyritic olivine basalt (above & below; above: ~6.5 cm across; below:
~4.0 cm across) - these two gorgeous pieces of lava are from the 13 January to
19 February 1960 Kapoho Eruption at the easternmost point of Hawaii. The
former town of Kapoho was located in the Kapoho Graben (Puna Rift Zone) segment
of Mt. Kilauea's East Rift Zone. Kapoho was famously burned, buried, and
destroyed by aa lava flows erupting continuously for a little over a month in
early 1960, despite the hasty construction of barriers. The lava flows overtopped
the barriers and even “burrowed under” the barriers. See the full Kapoho
Eruption story here, with field pics.
These rocks are vesicular porphyritic olivine basalts
(more technically, they can be called vesicular tholeiitic picrite
basalts). They have abundant subrounded to stretched vesicles and common
large greenish forsterite olivine phenocrysts. The basalt matrix is
glassy-looking, very finely crystalline plagioclase feldspar &
pyroxene. The large sample shown above has an obvious black-and-white
speckled xenolith of gabbro from the lower oceanic crust.
These particular samples are from the post-30 January
1960 phase of the Kapoho Eruption. Starting the 31st of January, it was
noted that large olivine phenocrysts were becoming common in the newly erupted
lavas.
RETICULITE
Reticulite (1.8 cm across) - here's a sample of reticulite (a.k.a.
thread-lace scoria). It is greenish-brown, highly vesiculated basalt
glass (sideromelane). Nearly all of the cells walls of the gas
bubbles have burst, resulting in a complex three-dimensional honeycomb
structure.
Reticulite forms during high lava fountaining
episodes. The honeycomb network is the result of extreme vesiculation
from vigorous gas escape as lava cooled ver quickly within the lava
fountain. Reticulite is very lightweight for its size (low density), and
is readily carried downwind.
Hawaiian reticulite is an incredibly fragile material,
having a dark, drab olive green color. Reticulite's glass threads
typically form hexagonal & pentagonal geometries. Despite its low
density, reticulite does not float in water - its porosity is too high.
ACHNELITHS
(PELE’S TEARS)
Achneliths (Pele's Tears) (from left to right, specimens are 9 mm tall, 10.5 mm
tall, 9.5 mm tall, and 18 mm tall)
Pele's tears are small, raindrop-shaped blebs of
quickly solidified basalt lava. The technical term for such structures is
achneliths. These Hawaiian achneliths represent rapidly chilled
basalt lava spray blown by winds during a high lava fountain eruption.
The broken tips of the three smaller specimens reveal that they are composed of
black, finely-vesiculated basalt glass (tachylite). In the field,
Pele's Tears are many times seen attached to the distal ends of extremely long
threads of mafic glass (Pele’s Hair - see below).
Locality & eruption info.: unrecorded locality on Hawaii, but probably derived
from a Mt. Kilauea eruption; unrecorded eruption date, but probably a mid- to
late-20th century high fountain eruption.
PELE’S HAIR
Pele’s Hair (above & below; above: field of view ~2.8 cm across; below:
field of view ~3 cm across) - Pele’s hair refers to extremely long threads of
brownish- to blackish-colored basalt glass (sideromelane &
tachylite). It forms as very fluid basalt lava spray is stretched while
airborne. Achneliths (Pele’s tears - the small, black, glassy structures)
are often found attached to one end of individual threads. Multiple
threads can be found attached to some achnelith masses.
Provenance: vintage 1930s tourist specimen; unrecorded eruption date; unrecorded
collection locality.
Achnelith (Pele's tear) with two attached threads of
Pele's Hair. Longest dimension of specimen is 9 mm.