Java Volcanic Eruption of Mount Merapi
By Ryan Frost


Indonesia lies on the “Ring of Fire” in the Pacific which comprises more than three-fourths of the world’s dormant and active volcanoes. (3) Due to this fact, Indonesia is home to more volcanoes than any other country in the world, with a total of 76. (1) It also has one of the world’s most active volcanoes. (1) It is a nearly 2,968 meter-high volcano known as Mount Merapi (“mountain of fire” [5]) and is located in Java. (4) Merapi is a stratovolcano that has had several eruptions throughout recorded history. Mount Merapit is the southernmost, youngest of the volcanoes in Java and is close by one of the most populated areas in the world, Yogyakarta. (18) The volcano is located near the Eurasian and Indo-Australian tectonic plates on top of a subduction zone. (19)

Java, Indonesia is located in the South-West region of the Ring of Fire.

Background Information

In 1930, Mount Merapi’s deadliest eruption killed about 1,300 people from the result of pyroclastic flows. (2) Pyroclastic flows are fluid-like mixtures of hot rock and gas that move very fast down the slope of a volcano due to gravity. (11) Pyroclastic flows can deposit sediments which can later cause lahars (or mudflows) if there is enough rain or other disturbance. Generally speaking, these lahars are responsible for the most amount of fatalities from a volcano. Merapi’s prior eruption was in 1994 which burned 60 people to death when the volcano sent out a scorching hot gas cloud. (1)

In 2006, Merapi erupted again and was experiencing a constant lava flow. (2) It all began in April of 2006 when there was an increase in seismicity in the area, and a lava dome began to form. The people who live along the slope of the volcano, who are clustered in four different groups, were informed that an evacuation might be called for soon. On April 23, due to more seismic activity the elderly and infants were evacuated (13). On April 26, this image below was taken of Mount Merapi (image 3). It shows that "a light plume of steam was rising from the summit" (12). May 11, seventeen thousand people were evacuated. Then two days later Indonesian Authorities decided that alerts had to be raised to their top-level and that they would force evacuations of all villages within an 8km (five-mile) radius. On May 27th, the threat continued, as a strong earthquake hit near by which may have disrupted the volcano, causing it to swell further. It was thought that this could cause a large enough eruption to reach those villages not yet evacuated, endangering many more lives. As a result, 12,000 more people left their homes to head towards shelters. (14)

(6) Residents live dangerously close to this active volcano.
(6) Residents live dangerously close to this active volcano.
Image 3. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite. Image from
Image 4. Farmer
Image 4. Farmer

(4) However, some residents refused to leave the area for different reasons. Some farmers say they cannot afford to leave their animals and crops which would leave them unable to support their families and have decided to wait for financial help from the government. Image 4 shows a farmer who held behind during the evacuation as he attempts to remove the fallen volcanic ash from his vegetables, nearly two miles from the eruption site. (15) Mount Merapi is also believed by many locals to be a place where mystical spirits dwell in the volcano’s crater, and are waiting for a certain signs from the mountain to let them now an eruption is coming. (5) Offerings were made and many live animals were sacrificed into the crater by these locals as they hoped for some natural warning in return. They kept their eyes open for lightning striking near the volcano or animals heading down the sides of the crater. (16)
On June 13th, 2006 Mount Merapi announced that they had lowered the alert level of the volcano from “alert” to “prepared” after the volcanic production had decreased in recent days. Officials had feared that because the volcano was building up since April, it could cause a large eruption. They concluded that the partial eruptions in late May reduced the pressure enough that there was no longer an immanent danger. (17)

What early warning systems have been implemented?

There have been a number of early warning systems developed for the region. Seismic activity is being constantly checked and deformation of the volcano is monitored via GPS data. (7) Lahar flood sensors have also been installed up stream along the Sat River on the West side of the volcano. (7) Then a siren is used during an emergency to warn of the coming danger. (7) They have also created an appropriately titled "MERAPI" Project (Mechanism Evaluation, Risk Assessment, Prediction Improvement) which is supposed to help predict the volcanos activity at different stages of its eruption process. This is done by examining Merapi's internal structure, its historical explosions, and its magma qualities. This project should help increase warning time. (8) The Merapi Volcano Observatory is also doing extensive monitoring on the volcano. (18) The seismic signals for Merapi are categorized into sixtypes: Va event (deepest tectonic-like seismic activity with clear indications between the P and S waves), Vb event (similar to Va, but the P and S waves are not easily identified), MP event (many phases that usually occur during lava dome formation), LF event (low constant, seismic activity), Tremor, and Guguran (landslide/ rock fall that comes from the lava dome). (19) Lahar monitoring is done in two steps. The first step is to estimate the potential volume of the loosened material on the slope. The second step is by using detectors to monitor lahar flows in river channels.

(10) Merapi spewing forth ash.
(10) Merapi spewing forth ash.


These early warning systems should prove crucial to the safety of the residents in Java, because another big eruption like the one of 2006 would place more than one million local inhabitants in immediate danger. (8) Of course, the best move for those living in the destructive path of Mount Merapi is to relocate to another location. However, due to their religious beliefs and current economic state, it is unlikely many will be willing to move.