When did Semeru Last Erupt? Learn the Eruption Type and Volcanic Status

Semeru, the highest mountain on Java Island, has routine activity. It regularly erupts every year. The volcanic activity has been getting more intense since the beginning of 2025. When did Semeru last erupt? The last eruption occurred in December. Its peak activity always occurs at the end of the year, precisely during the rainy season.

When did Semeru Last Erupt?

In 2025, Semeru actively erupts as always, with a steady increase in its activity. At the beginning of the year, increased activity has been seen and marked by volcanic earthquakes.

The first eruption occurred and raising the status to Advisory (Level II) on July 9^th. An ash column 1 km high and pyroclastic flows 4 km long are the impacts of this eruption. The incandescent lava flows emerge in the next eruption on September 23^rd. The status is changed to Alert (Level III). The thick gray smoke and incandescent lava emerge in mid-November as a mark of intense activity.

The activity is continuously increasing, and the peak activity occurred on November 19^th, 2025. It is marked by a pyroclastic flow as far as 5.5 kilometers. Strong earthquakes followed by a massive fall. The status was immediately raised to Warning (Level IV).

From November 19-28, volcanic activity is trending upward. However, conditions can be controlled because the strong magma didn’t emerge, and deformation remained stable. The following day, November 29^th, a small to moderate eruption occurred, but no magma pressure was detected. The status was downgraded to Level III.

Several eruptions occurred during December 3-28. At the end of this year, a total of 38 eruptions and two distant tectonic earthquakes occurred on December 29^th.

The Eruption Type and Pattern

Many factors influence the type of eruption. The main factors are gas pressure and the depth and extent of the magma chamber. The next factors are magma viscosity and its interaction with water (phreatomagmatic). Moreover, the volcano type helps determine the eruption type.

Semeru is categorized as a stratovolcano. It indicates that Semeru has a mixed eruption type that consists of explosive and effusive. It is followed by thicker magma, creating steep, layered slopes.

An explosive eruption has a higher impact because characterized by the release of solid material (pyroclastic flows) sometimes destroys the lava dome. An effusive eruption is a molten eruption, where lava flows out and produces avalanches. Although they happen alternately, the explosive eruption occurs more frequently. The impact is higher, especially if there are high and strong eruptions.

Having an explosive eruption and a cone-shaped peak are the reasons why Semeru has a higher eruption plume. It threatens many areas. It is a match with the most powerful eruption on November 19^th, 2025, as an explosive eruption.

Semeru has an anti-mainstream eruption pattern. It is the peak activity occurring at the end of the year, specifically during the rainy season. This condition increases the risk because eruptive material is immediately washed away by rainwater and triggers a lava flood if it is in high volume.

The Volcanic Status

When did Semeru last erupt? All Semeru activity is monitored and recorded by a monitoring system connected to a detector. This detector is also connected to a disaster warning system, providing immediate early warning to the public if there is a potential eruption. To indicate increased volcanic activity, there are four levels of categories.

1. Normal

The purpose of volcanic activity classification is to indicate the level of activity and the risks posed. The first level is normal. The volcano is in normal condition. Although there are fluctuations in activity, they are not significant. The impact is limited in the eruption center, which presents toxic gas emissions. Status determination is based on visual and instrumental observations.

2. Advisory

The second is the advisory level. The seismic and volcanic activity is beginning to appear. The signs are mild volcanic earthquakes and increases in temperature, gas, and smoke. Minor eruptions are triggered by these conditions. It threatens the crater area.

3. Alert

Increased activity is becoming increasingly evident at this third level. The seismic and volcanic activity has significantly increased. The increasing factors are volcanic earthquakes, lava flows, deformation of the volcano's body, and the emergence of pyroclastic flows.

A major eruption is expected in the short term, about two weeks again. The impact of the eruption reached the peak area, slopes, and rivers that originate at the peak.

4. Warning

Warning is the highest-risk level that indicates the peak of volcanic activity. This condition has the highest possibility for an eruption. Before an eruption occurred, the initial signs appeared first, such as the intense emergence of hot clouds, incandescent lava, ejection of incandescent rocks, and ash fall.

At level IV, a major eruption is possible, accompanied by ash, debris, and steam. The safety zone needs to be established because the impact of a major eruption extends to residential areas. For safety reasons, the red zone should be avoided.

When did Semeru last erupt? This can be determined through a monitoring system. In disaster mitigation, the monitoring system is connected to an early warning system. The early warning system is crucial to reducing the risk of volcanic eruption effectively. This early preparation is useful for facilitating evacuation and recovery after disasters.

In implementation, there is not sufficient if only providing warning signals via alarms or sirens. Emergency messages are needed to provide complete information. The government can procure an emergency message-sending machine.

The message-sending machine is based on SMS (Short Message Service), allowing it to send messages to mobile phones in real time. It has a wide range of up to 2 km for all operators. This specific machine can be purchased at smsbroadcaster.com. Product photos and complete information are available.