Geological Agency: Demak land subsidence 5-11 cm per year, ancient strait reestablishing not realistic

Semarang – Despite significant land subsidence along the Demak coast, the Head of the Geological Agency of the Ministry of Energy and Mineral Resources (EMR), Muhammad Wafid, emphasised that speculation about the possibility of the Muria Strait, which disappeared about 300 years ago, being re-established is not realistic.

The Muria Strait is a strait separating Java Island from Muria Island, a landmass around Mount Muria in Central Java, separated from the mainland about three centuries ago. The strait between Semarang and Rembang gradually narrowed due to sedimentation and then merged with mainland Java.

Wafid emphasized that although the annual land subsidence is quite significant, the geological factors required to reshape the Muria Strait are complex and not limited to land subsidence.

“In the Demak coastal area, the speed of land subsidence is estimated to range from 5 to 11 cm/year. Some places in the coastal area have a lower elevation than the sea level so that it will protrude far into the land in the event of a tidal flood. Although there is land subsidence in Demak and surrounding areas, the Muria Strait does not mean it will re-form soon. The current flood, which took a long time to recede, is more influenced by the climate, namely high rainfall and infrastructure damage,” said Wafid in an official statement on Monday, March 25.

Wafid clarified that apart from land subsidence, other factors such as subsurface soil structure and climate change resulting in sea level rise must also be considered in this context. He says the Muria Strait will not re-form except through extreme geological processes, such as a very large tectonic earthquake.

“Theoretically, the Muria Strait may be re-formed if a powerful geological process occurs, such as a very large tectonic earthquake that causes a sudden graben and covers a large area,” Wafid explained.

However, according to research by the Geological Agency, although significant subsidence exists in some coastal areas, more is needed to cause the reshaping of the Muria Strait directly. Wafid added that the process would take a very long time, even on a geological time scale, requiring uniform subsidence from Demak to Pati.

“Facts in the field based on research by the Geological Agency show differences in the speed of land subsidence, where in coastal areas it is faster than inland. Some estimates of the dominant factors of the possibility of re-forming the Muria Strait are the occurrence of large land subsidence, accompanied by rising sea levels due to climate change and disruption of river flow patterns because the land elevation is lower than sea level,” concluded Wafid. (Hartatik)

Banner image: Gunawan Kartapranata (original author)/Wikimedia commons, CC BY-SA 3.0, 

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