Semeru's Three Eruptions Are Not Related to the Bawean Earthquake

Semeru experienced three eruptions on Saturday morning. PVMBG stated that Semeru's activities were not related to the Bawean earthquake.

The following article was translated using both Microsoft Azure Open AI and Google Translation AI. The original article can be found in Tiga Kali Erupsi Semeru Tak Terkait Gempa Bawean

KOMPAS/BAHANA PATRIA GUPTA

Mount Semeru seen from Supiturang Village, Pronojiwo District, Lumajang Regency, East Java, Monday (5/12/2022).

MALANG, KOMPAS — Mount Semeru in Lumajang Regency, East Java, Saturday (23/3/2024), experienced three eruptions with the eruption column height observed at 1,000 meters above the peak. The status of the mountain as high as 3,676 meters above sea level is still on alert or level 3.

Based on data from the Center for Volcanology and Geological Hazard Mitigation (PVMBG), the first eruption occurred at 05:44 with an observed eruption height of about 600 meters from the peak. The ash column was white to gray in color with thick intensity towards the north. The eruption was recorded on a seismograph with a maximum amplitude of 22 millimeters (mm) and a duration of 112 seconds.

The second eruption occurred at 07:28 with an eruption column height of 700 meters above the peak. The ash column was observed by residents similar to the previous eruption, which was white to gray with thick intensity to the northwest. The eruption was recorded on a seismograph with a maximum amplitude of 20 mm and duration of 75 seconds.

The third eruption occurred at 08:07 with a eruption column height of 1,000 meters above the peak. The ash column was observed to be white-gray with thick intensity towards the northwest. The eruption was recorded on the seismograph with a maximum amplitude of 21 mm and a duration of 73 seconds.

Previously, on Friday (March 22, 2024) at 9:58 pm, Semeru also erupted. The eruption column reached a height of 1,000 meters above the summit with a gray-white ash column with thick intensity towards the northeast and north. The seismograph recorded a maximum eruption amplitude of 22 mm with a duration of 138 seconds.

KOMPAS/DAHLIA IRAWATI

On Sunday (24/4/2022), the community watched the Gladak Perak suspension bridge in Lumajang, East Java. The bridge broke due to the impact of the Semeru eruption on December 4, 2022.

Head of the Volcanology and Geological Disaster Mitigation Center (PVMBG) Volcano Working Team, Heruningtyas Desi Purnamasari, said that the activities occurring in Semeru had nothing to do with the consecutive earthquakes that occurred in Bawean.

Based on the evaluation results of PVMBG for the period of March 16-22, which was signed by PVMBG Head Hendra Gunawan on March 23, 2024, from the visual observation side, the mountain body was clearly visible until it was covered by fog. When physically observed, the smoke from the main crater was white and grey with a thin intensity of 100-200 meters from the peak.

Gray-white eruption smoke rose 200-1,000 meters high from the peak towards the northwest-northeast. The eruption and lava flow are rarely observed visually due to the hindrance of fog, and there are sometimes rumbling sounds during eruptions.

Also read: Fresh Javanese Langur Blood for Genetic Variation in Semeru

From an instrumental observation perspective, the number and types of earthquakes recorded are still dominated by surface earthquakes, such as eruptions and gusts. During March 16-22, there were 604 eruption/eruption earthquakes, 10 avalanche earthquakes, and 109 gust earthquakes, 49 harmonic earthquakes, 8 deep volcanic earthquakes, 1 local tectonics, 51 distant tectonic earthquakes, and 1 flood shaking earthquake.

Rarely observed

Semeru activity on March 16-22 showed that eruptive activity, hot clouds and lava avalanches were still occurring, but were rarely observed visually due to the weather. The accumulation of material resulting from the eruption or the formation of scoria cones has the potential to become incandescent lava avalanches or hot clouds.

The material of lava or hot clouds that accumulated along the river streams originating from Semeru has the potential to become lahars if they interact with rain. The interaction between the deposited materials of lava or hot clouds with high temperatures and the river water potential to trigger secondary eruptions.

KOMPAS/DEFRI WERDIONO

The beautiful agricultural landscape of Ngadas Village, Poncokusumo District, Malang Regency, East Java, with the backdrop of Mount Semeru covered in clouds, on August 28, 2020.

"During this period, the recorded number of earthquakes shows that seismic activity in Semeru is still high, especially for explosive earthquakes, rockfalls, and harmonic tremors. The recorded volcanic and harmonic tremors indicate that there is still a supply of magma beneath the surface and a build-up of material from eruptions around the Jonggring Seloko crater," he explained.

Deformation monitoring using tiltmeter and continuous GPS equipment during this period is still fluctuating. However, at the end of the observation period, there is a relatively decreasing pattern on the lower part of Semeru's body. Meanwhile, the upper part shows an inflation process that correlates with pressure displacement from inside the mountain to the surface, along with the material discharge during the eruption.

Agus Harianto, one of the residents of Supiturang, Pronojiwo District, Lumajang, confirmed the eruption on Saturday morning and Friday night. To his knowledge, Semeru had experienced a similar eruption a few weeks ago. "We didn't see any pyroclastic flow, only a column of eruption," he said.

Also read: Semeru Volcanic Ash Has Disturbed Flights in Malang

KOMPAS/BAHANA PATRIA GUPTA

Residents who are victims of the eruption of Mount Semeru and will perform Eid al-Adha prayers are currently staying in several places in Candipuro District on their way to Baitul Adim Mosque in Curah Kobokan Village, Pronojiwo District, Lumajang Regency, East Java, on Sunday (10/7/2022).

Agus stated that there is no panic among the residents regarding this matter. They are still carrying out their activities as usual. Coincidentally, the weather in the Semeru mountain range has been clear for the past two days, compared to the previously cloudy and windy conditions at the top.

Regarding the activity of Mount Semeru, the PVMBG is still issuing several recommendations, including that the community should not engage in any activities in the southeast sector along Besuk Kobokan, up to 13 kilometers from the peak (eruption center).

During this period, the recorded number of earthquakes indicates that seismic activity in Semeru is still high, especially for eruption, landslide, and harmonic earthquakes.

Beyond that distance, the community does not engage in activities within 500 meters from the river's edge (river boundaries) along Besuk Kobokan because of the potential for hot cloud expansion and lava flow up to 17 kilometers from the peak. In addition, residents do not engage in activities within a radius of 5 kilometers from the crater/peak of Semeru because of the risk of falling rocks (pyroclastic flows).

Residents should also be wary of the potential for hot clouds, lava flows, and lahars along the rivers/valleys that originate from the peak of Mount Semeru, especially along Besuk Kobokan, Besuk Bang, Besuk Kembar, and Besuk Sat, as well as the potential for lahars in the small rivers that are tributaries of Besuk Kobokan.