FILLMORE CRATERS
VOLCANISM
The “Black Rock Desert”, due west of Fillmore in
west-central Utah’s Sevier Desert, has some nice basalt lava flows. The rocks shown below are from there - these
represent Holocene-aged Fillmore Craters volcanics (<10,000 years
old). The lavas are pretty rough & jagged. The rocks themselves
range from lightweight scoriaceous basalts to heavier vesicular
basalts. The surface morphologies of the scorias show that many
formed by stretching of sticky lava during cooling - this can be seen at active
aa lava fronts in Hawaii.
Stretched scoriaceous basalt (7.0 cm across)
Stretched scoriaceous basalt (above & below) (above: longest dimension
9.2 cm; below: field of view ~4.0 cm across)
Some Fillmore Craters volcanic rocks are parts of lava
tubes. Many basaltic lava fields in western America have well developed,
small to large lava tubes. The ceilings of the lava tubes often have a
“bloopey” appearance to them. These are lavacicles - they hang down from
the ceiling and have a distinctive chocolate batter-like sheen.
Vesicular basalt - cross-section of a lava tube ceiling.
Lavacicles and
vesicular basalt (above & below; field of view ~8.5 cm across) from the
interior surface of a basalt lava tube ceiling.
