- A new study shows deep magmas have more than 10 weight-percent of water.
- We need to develop a new technique to analyze how much water is actually present in magma.
Few things in nature are impressive and frightening at the same time. Magma is one of those things. It is the molten or semi-molten material from which all igneous rocks are formed.
Volatile components in magma, such as water, lead to explosive volcanic eruptions. Estimating the amount of volatile content present in magma [before the eruption] is a tricky part. And the fact that scientists only analyze the final component (after all the volatiles have been lost) makes this estimation even difficult.
Recently, a team of researchers in the United States came up with strong evidence suggesting that magmas may contain more water content than previously estimated. The findings show that deep magmas have more than 10 weight-percent of water.
Standard Technique For Estimating Volatile Components In Magma
To determine volatile content in Magma, scientists usually analyze tiny chunks of magma confined in crystals erupted in lava. Analysis of these glassy inclusion enables them to measure the amount of hydrogen present, which indicates how much water magma contained before the volcano erupted.
This common technique is considered as a precise lower limit on volatile components in magma. However, researchers wanted to investigate the upper limit – something that hasn’t been studied until now.
The research team synthesized melt inclusions in the laboratory to accurately determine how much water a melt could possibly contain. They recreated the environment (high pressure and temperatures conditions) that exists 25 miles below the surface of the Earth.
Image credit: Ralf Lehmann via Shutterstock
The magma sample was then melted and rapidly cooled in this environment. Researchers carefully analyzed the sample to see whether these experiments produced a glass. They then added more water to the sample until it could no longer be transformed into a glass.
Finally, they came to the conclusion that samples containing an excess amount of water do not form a glass. Although such nonglassy melt inclusions exist below the Earth’s surface, they are not preferentially analyzed for volatiles. So you can say that most studies in this field have been sample biased.
If magmas in deeper layers of Earth contain over 9 weight-percent of water, existing methods won’t be able to measure them correctly. Therefore, we require a new technique to analyze how much water is actually present in magma.
This study indicates that analyzing the mineralogy of non-glassy melt inclusion found in rapidly cooled environments like small lapilli or ash deposits for the presence of smectites or chorites could be used to detect super-hydrous magmas.