Earth and Mars both show evidence for a wide range of volcanism. However, constraining the eruptive styles on Mars is trickier than on Earth due to more limited observations. Undergraduate student Kellie Wall, from Washington State University, has led a team of researchers in developing a technique to determine whether or not a volcanic rock has interacted with water during its eruption based on its texture.
This study looked at 17 different types of volcanic rock on Earth, and found a link between the amount of crystallization and eruptive style. Explosive volcanic eruptions can be divided into two groups depending on whether water (or ice) has interacted with the magma or not. Phreatomagmatic eruptions, for example the 1991 eruption of Mount Pinatubo, are ones where magma has come into contact with water and ones which haven’t are simply known as Magmatic, for example Stromboli or Vesuvius.
X-ray diffraction (XRD) analyses of the samples quantified the crystallinity of each sample and it was found that Phreatomagmatic material contains a lower proportion of crystals than Magmatic styles. This result is inkeeping with the observations that when molten rock interacts with water it cools very rapidly and is predominantly glass, whereas without water the rock takes longer to cool and therefore more crystals form and grow.
To apply these results to Mars, the physical differences in eruption styles due to the different atmospheric pressure conditions have to be accounted for. XRD analyses from a number of sites across the Martian surface from the Mars Science Laboratory Curiosity Rover suggest that the widespread signature of volcanism on Mars is not influenced by interaction with water. This method could now be applied to other Martian rocks or other planetary basalts.