Magma fragmentation and volcanic eruption style

5 problems

• What decides whether an eruption is explosive or effusive?

  Open

  The same volcano, with similar magma, can erupt explosively one time and quietly the next. The deciding factors seem to be how fast magma rises and how much gas escapes on the way up, but no model predicts the style beforehand.

• Why does most volcanic unrest end without an eruption?

  Open

  Volcanoes often swell, shake and release gas for months, then calm down without erupting. Telling apart unrest that will lead to an eruption from unrest that will fade is one of the hardest parts of volcano forecasting.

• What criterion decides when rising magma shatters into ash?

  Contested

  As magma rises, gas bubbles grow until the frothy melt may break apart into fragments and gas, turning a lava flow into an explosive jet. Scientists still disagree on which condition sets the break point.

• How long do crustal magma reservoirs persist as crystal mush?

  Contested

  Under many volcanoes magma is stored for long times as a crystal mush, mostly crystals with a little melt between them. How long it stays there and at what temperature is debated.

• How do locked crystal mushes become eruptible within decades?

  Open

  A mush that is mostly crystals cannot flow, yet crystal clocks show it can be turned into eruptible magma within years to centuries before an eruption. How that happens so fast is unclear.