Powerful eruption of Ubinas volcano

By Jose Prieto (EUMETSAT) and Sancha Lancaster (Pactum)

Ubinas is a stratovolcano in the Moquegua Region of southern Peru, 60 km east of the city of Arequipa. Part of the Central Volcanic Zone of the Andes, it is 5,672 m above sea level. On 19 July a powerful eruption spewed ash five km high above the mountain, which spread across parts of southern Peru.

In the area around Ubinas, it was reported that nearly 30,000 people were evacuated and airports closed. The plume crossed southern Brazil and reached the Atlantic at 13 km high, as a sulphuric gas plume 1,800 km long and 270 km wide, progressing at a speed of 150 km/h. It continued its trip into the Indian Ocean on 22 July (Figure 3).

The animated GOES-16 Dust product sequence (Figure 2) shows the eruption onset shortly before 07:30 UTC, launching gas (green) and ash (red) eastwards.

The stable stratification at the upper limit of the troposphere enables the generation of gravity waves, like the folds of an accordion. Under the gas lines we see the ashes at lower level, propagating almost parallel to the gas, particularly noticeable around 13:30 UTC, as in Figure 1 .

Gravity waves are high frequency internal perturbations in the air, generated by buoyancy under vertical stability. In this volcano case, the buoyancy frequency can be estimated from the propagation speed (70 km/h) and the crest separation (12 km) at around (1/600)Hz. Mesoscale convection can lead to wavelengths between 10 km and 1,000 km, although for convection the lack of a tracer on satellite imagery makes them hard to spot. For the night time, water vapour in the 6 µm absorption band often plays that role.

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