Does mt st Helens have pahoehoe or AA lava?

Answer 1

Niether. Pahoehoe and a'a are both varieties of basaltic lava. The material from Pinatobo is of a dacitic composition, which is much more viscous than a'a or pahoehoe. It tends to erupt explosively, producing ash and pumice rather than lava flows. When dacitic lava does flow it creates a block lava flow.

Answer 2

Neither. Pahoehoe and a'a only refer to lavas that form basalt when they cool and have essentially the same composition. The material from Mt Merapi has a different, more silica-rich composition that forms a kind of rock called andesite. It tends to produce clouds of ash and pyroclastic flows rather than lava flows.

Answer 3

Niether. Pahoehoe and a'a are both mafic in composition, and form a rock called basalt when they cool. The lava produced by Mount St Helens has a different composition. It forms a kind of rock called dacite. This lava is so viscous that it barley flows. In the case of Mount St Helens it has built into a dome rather than flowing down hill.

Answer 4

Neither. There are more kinds of lava than a'a and pahoehoe. Both of these are texture varieties of mafic lava, which cools to form basalt. Mount Rainier erupts lava of a different composition of an intermediate composition, which contains more silica than mafic lava and forms andesite when it cools. This lava is far more viscous than a'a or pahoehoe.

Answer 5

Niether. Pahoehoe and a'a are terms that apply to lava with a mafic composition (low silica content, low viscosity). Tambora's massive 1815 eruption would have produced ash and pumice, but not lava flows. An eruption as explosive as that usually indicates felsic material (high silica content, very high viscosity), which will form block lava rather than a'a or pahoehoe.

Answer 6

Neither. A'a and pahoehoe are lava flows that occur when basaltic lava is erupted in a non-explosive fashion. Vesuvius erupts exolisvely, producing clouds of ash and pumice rather than lava flows, and the material is of a different composition from the lava that forms a'a and pahoehoe. If it were to come out as lava, it would form a block lava flow.