Significant eruption at Merapi volcano, ash to 12.2 km (40 000 feet) a.s.l., Indonesia


A significant eruption took place at the Indonesian Merapi volcano at 06:40 UTC on January 27, 2021. The Aviation Color Code was raised to Red.

Due to the meteorological cloud, ash estimate to 12.2 km (40 000 feet) above sea level was based on the IR temperature. Ash cloud is moving NNW, the Darwin VAAC reports.

Multiple ground reports warned of a significant eruption, the center added.

In addition, volcanic ash below 7.3 km (24 000 feet) a.s.l. is expected to move NE.

The volcano produced at least 14 pyroclastic flows today, with a maximum distance of 1.5 km (0.93 miles).

This time, pyroclastic flows were observed on the southwest flanks of the volcano, reaching Krasak and Boyong rivers.

As a result, ashfall was reported in several villages in Tamansari District, Boyolali Regency, and Boyolali City.

BPPTKG reported that the '2021 lava dome' continued to emerge just below Merapi’s SW rim from January 8 to 14, producing a total of 128 incandescent lava avalanches that traveled as far as 900 m (3 000 feet) down the Krasak River drainage on the SW flank.

A comparison of photos taken on January 7 and 14 showed that the morphological changes in the summit area were attributed to the emergence of new lava domes.

The 2021 dome volume was an estimated 46 766 m3 (1.6 million feet3) on January 14, with a growth rate of about 8 500 m3 (300 000 feet3) per day.

Deformation continued, though at a lower rate; Electronic Distance Measurement (EDM) data showed a distance shortening between points in the NW at a rate of 6 cm (2.3 inches) per day. 

On January 16, pyroclastic flows descended 1.5 km (0.9 miles) down the Krasak drainage and produced an ash plume that rose up to 500 m (1 640 feet).

The Alert Level remains at 3 (on a scale of 1-4). The public is warned to stay 5 km (3.1 miles) away from the summit.

Geological summary

Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to the Ungaran volcano.

Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2 000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. 

Subsequently, the growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent eruptive activity, began SW of the earlier collapse scarp.

Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities during historical time. (GVP)

Featured image credit: CVGHM

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