What are the different types of lava flows?
What are the kinds of rocks formed from lava and what are their uses?
Sharon Penley
Dear Sharon,
There are three types of lava and lava flows: pillow, pahoehoe, and
aa. Pillow lavas are volumetrically the most abundant type because they
are erupted at ocean ridges and because they make up the submarine
portion of seamounts and large intraplate volcanoes, like the
Hawaii-Emperor seamount chain. Pahoehoe is the second most abundant type
of lava flow.
Eruptions under water or ice make pillow lava. Pillow lavas have
elongate, interconnected flow lobes that are elliptical or circular in
cross-section.
"Pahoehoe" and "aa" are Hawaiian words that describe lava. Pahoehoe
lava is characterized by a smooth, billowy, or ropy surface. Pahoehoe
flows tend to be relatively thin, from a few inches to a few feet thick.
In map-view the flows tend to be narrow and elongate.
Aa is characterized by a rough, jagged, spinose, and generally
clinkery surface. Aa lava flows tend to be relatively thick compared to
pahoehoe flows. During the early episodes of the current eruption of
Kilauea volcano, aa flows up to 36 feet (11 m) thick surged through the
Royal Gardens subdivision at rates as great as 108 ft/min (33 m/min).
Pictures in
Hawaiian Tour Guide
illustrate many
of the points noted above.
All volcanic eruptions produce lava. The lava can take one of two
forms: lava flows or pyroclastics. We already described lava flows.
Pyroclastics are pieces of lava explosively thrown out of a volcano by
the expansion of gas bubbles. Pyroclasts can take many forms depending
on the violence of the eruption, type of eruption, and composition of
magma/lava. Two types of pyroclasts that I'm sure you are familiar with
are ash and cinders. Ash is produced by very violent eruptions that
fragment the lava into pieces smaller than 2 mm (0.08 inch). An
excellent example of an ash producing eruption is the May 18, 1980,
eruption of
Mount St. Helens. Cinders are pieces
of fragmented lava in the size range of
2-64 mm (0.08-2.56 inches). A good example of an eruption that produced
a cinder cone is
Paricutin
in central Mexico.
Lava and pyroclasts have a variety of uses including building or
ornamental stone and road material. Volcanic rocks also make an
excellent substrate for agriculture.
Thank you for your question.
Steve Mattox, University of North Dakota
A similar question was answered by Scott Rowland. To gain
Scott's
perspective visit Questions about Lava in Ask a Volcanologist.
Other Categories
Other Questions
To VolcanoWorld