The recent eruption of the Tonga volcanic eruption (2022) was so powerful that the shockwave from the eruption was captured in sensors worldwide. How do pressure sensors work, what was reported, and what can be inferred from sensors all around the world?

The Tonga volcanic eruption

On the 13th of January at 3.10pm GMT, an underwater volcano in Tonga erupted. The volcano itself resides on the “ring of fire”, which refers to the perimeter of the Pacific Ocean that is responsible for many active volcanoes, and the specific volcano that erupted was just 65km from the capital of Tonga, Nuku’alofa.

As the volcano erupted, thousands living near the coast of the islands were warned by local authorities to seek higher ground to avoid the oncoming tsunami. What made the volcanic eruption particularly worrying was that while the volcano did partially erupt a few weeks before, it had been declared dormant on the 11th of January, just two days before its eruption. The resulting plume from the eruption was estimated to have a final height of 30km and a diameter of 260km.

The deviation caused by the eruption was limited to the immediate area. Still, many around the world, including those in the US and UK, could detect the eruption themselves. It turns out that the pressure wave created by the volcano was powerful enough to be detectable by pressure sensors around the world. In fact, there have even been some reports of makers having detected the pressure spike with their own DIY projects.

How do pressure sensors work?

It is amazing that sensors around the world are sensitive enough to detect pressure waves from volcanic eruptions from thousands of kilometres away. But exactly how do pressure sensors work? The most common pressure sensor takes advantage of piezoresistive sensors placed on the perimeter of a diaphragm. Basic pressure sensors will use a fixed air cavity below the diaphragm, but more advanced sensors can connect this cavity to a reference port so that the pressure sensor can work in a wider range of pressures.

Simply put, as the external air pressure increase, the diaphragm will bend into the air cavity, and this bending of the diaphragm increases the electrical conductivity of the multiple piezoresistive elements. These elements are connected in a whetstone bridge, and the resulting voltage produced corresponds to a pressure reading relative to the air cavity.

How will the increased use of sensors help researchers?

When it comes to understanding nature, data is everything and the more data that researchers can get, the better. But for such data to be useful, it needs to be varied in source and time as this can help provide a better picture. For example, a million pressure sensors could have surrounded the volcano, but all of this data would be essentially useless as it would only provide researchers with repeats of the same data (having been taken at the same time and the same distance).

However, having a million pressure sensors worldwide provides researchers with pressure wave data as it moves around the planet and what time the pressure wave arrived and how powerful it is. This allows researchers to better understand how the pressure wave from the volcanic eruption moved around the Earth’s atmosphere and crust and determine the time between pressure wave detection and resulting tsunamis.

The increasing use of sensors in everyday life could potentially provide researchers with the perfect tool for monitoring the environment. In fact, this is already happening with Google having recently experimented with detecting earthquakes using users’ phones. The idea behind this is that by detecting tremors before they cause damage, people can be given precious seconds to get to cover.

It is exciting to see the pressure wave from the Tonga eruption being detectable in the US and UK, and the widespread reports from makers and professionals alike could give researchers valuable insight.