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On 10 July 2023 at 16:40 UTC there was an eruption of Fagradalsfjall volcano on Iceland’s Reykjanes peninsula southwest of Reykjavik.

 

Less than seven hours later the fissure vent eruption was recorded by the German hyperspectral satellite EnMAP (Environmental Mapping and Analysis Program). EnMAP has over 224 spectral bands available in the wavelength range between 420 and 2450 nanometers – in visible as well as near and shortwave infrared wavelengths – at a 30 meter ground resolution.

 

EnMAP False colour image recorded 10 July 2023; 23:30 UTC (spectral bands 193,149,75);
EnMAP data © DLR 2023. All rights reserved

 

The evening recording combines three spectral bands in the for-us-invisible infrared range into a so-called false-colour image. Because of the high temperature of the lava the discharge vent is readily visible in shortwave infrared despite the smoke and heavy cloud cover. The high intensity of the radiation in areas close to the eruption even leads to saturation in some of the bands. In contrast, the signal coming from the clouds is very weak and at the border of what can be detected by the sensors. The clouds also cause a noticeable dispersal of the radiation, which especially hinders identification of temperature dispersal and the spreading out of the lava on the ground. During the day the signal consists of a combination of emitted thermal radiation and reflected solar illumination.

 

EnMAP False colour image recorded 12 July 2023; 13:00 UTC (spectral bands 209,142,14);
EnMAP data © DLR 2023. All rights reserved

 

 

 

On 12 July 2023 at 13:00 UTC EnMAP was able to make another imaging spectrometric recording. Since the volcano was then not concealed under clouds it is possible to unambiguously identify the dust and gas cloud that was carried by the wind into a southwesterly direction, in addition to the clearly visible discharge vent and temperature dispersal. In a comparison of the first and second EnMAP recordings it could also be noted that the intensity of the eruption had clearly weakened in that interval.

 

 

 

A comparison of the spectrum of an image pixel from EnMAP at the centre of the eruption (blue) with spectra of thermal emissions resulted in an estimated temperature of some 800 °C (red), which is compatible with rhyolithic lava. Because of the expected saturation of some of the spectral bands the estimate was based only on the wavelength range between 800 and 1300 nanometers.

In addition to this example of a way to estimate high temperatures that are otherwise normally derived from mid- and long-wave infrared radiation, EnMAP data also yields other information related to the eruptions thanks to its high spectral resolution. For example, the absorption of carbon dioxide (CO2) in the atmosphere in the wavelength range around 2060 nanometers allows conclusions to be drawn about changes in CO2 concentrations near the volcano, which emits CO2 during an eruption.