On 15 January, the island state of Tonga was rocked by a massive eruption from the nearby Hunga Tonga-Hunga Ha'apai volcano. Satellite images of the eruption were quickly shared showing clearly the scale and power of the explosion. These images were virtually the first source of information considering the archipelago was virtually inaccessible due to a damaged undersea communication cable.
The optical images from weather satellites clearly showed that an eruption has taken place, only they do not show the situation on the ground; as the ash cloud blocks visibility. Radar satellites can do this. The European Sentinel-1A satellite uses a special kind of radar waves that can see through clouds and ash, as it were. Data from this satellite therefore immediately showed that the volcanic island was almost completely destroyed by the eruption.
After the ash cloud moved away, it also became possible to use other satellites to look at the archipelago to also determine the impact on its inhabitants. Planet images, for example, clearly show the devastating effects of the tsunami caused by the eruption. For now, satellite images are the best indication of the damage given the limited communication capabilities with the archipelago.
Another important aspect of volcanic eruptions is the emission of harmful gases such as nitrogen dioxide (SO2). These gases can be detected using the Netherlands-produced Tropomi sensor on the Sentinel-5P satellite. It is important to be able to estimate the released SO2 as it can have a huge impact on the climate because SO2 in the atmosphere reflects radiation. The first indication is that the amount of emitted SO2 (approx. 400,000 tonnes) will have no or negligible impact on climate, but the situation is being closely monitored.
In the past, a volcanic eruption like this one in a remote area like Tonga might go unnoticed and help might not arrive until late. Today, satellite data can be used to quickly assess what happened, what the damage is and what the further consequences will be. Thus, harmful gases can be monitored, tsunami warnings issued and important damage estimates made. A disaster like this therefore underlines the value of satellites in providing important insights quickly.
