How Do We Know How Tall Prehistoric Volcano Plumes Were?

QUESTION: When experts study volcanic eruptions that happened thousands of years ago, how do they know how tall was the eruption column?

I was watching a documentary about Phlegraean Fields in Italy and they said that when it erupted 39 thousand years ago, the eruption column reached about 30km high (18 miles).

So I was wondering, how do they know how tall it was? What do they do to determine its height?

Thanks gang. 
Maisy"

Thank you for the great question Marlene.

Volcanoes leave behind a trail of evidence, much like a crime scene. Geologists examine volcanic deposits like ash layers and rocks, piecing together the eruption's intensity and the height of the ash column.

The distance travelled by volcanic ash is a key clue. Imagine throwing a pebble – the harder you throw, the farther it goes. Similarly, a powerful eruption with a high ash column can propel ash over vast distances. By studying the thickness and distribution of ash deposits, scientists can estimate how high the eruption column must have reached to carry the ash so far.

Wind also plays a role. Just like a strong breeze can affect where a thrown pebble travels, wind currents can influence the path of an eruption column. By analysing the grain size and distribution of ash deposits, geologists can estimate wind speeds and the direction the ash plume travelled. This information, combined with the distance travelled, helps them piece together the height of the eruption column.

Modern computer models also come into play. Scientists can feed data on the volume and distribution of volcanic deposits into these models. The model then simulates the eruption, factoring in wind speed and magma properties. This helps them recreate the eruption dynamics and estimate the eruption column height.

Determining eruption column height isn't an exact science. Geologists use a combination of these techniques, along with analysing features like volcanic craters and calderas, to build the most accurate picture possible.

Volcanologists are constantly refining their methods and incorporating new discoveries. The quest to understand these ancient giants continues, helping us better predict and prepare for future eruptions.

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