Cold Lahars Displacing People at Mount Merapi, Indonesia

Dredging in the Code River, Yogyakarta
Photo from here.

Eruptions at Mount Merapi, discussed here, here, and here before in this blog, produced ash and other debris that sits atop the mountain awaiting the monsoon rains. Those rains have arrived; the wet monsoon season in Indonesia lasts from November through March. For weeks muddy torrents have been flowing down from the mountain. On November 30 an apparently big one, reported to be up to 2 meters deep, arrived. According to the Nov. 30 edition of the JakartaGlobe, thousands of residents were forced to evacuate. These muddy flows of volcanic materials are termed "lahars", and they can be either hot or cold depending on the timing of the volcanic activity and the weather.

The lahars flow down the channel of the Code River, which flows through the center of Yogyakarta.  The river has been channelized to control the path of the lahars, a historic danger from Merapi. Sandbags up to 1 meter high help control the flows, but authorities have warned residents that these temporary levees will not contain the large flows that are likely to occur.  Surono, the head of the Volcanology and Geological Disaster Mitigation Agency (PVMBG) has warned that people should stay 300 meters away from the river.  Evacuation has been hindered by damage to roads and bridges, as well as by heavy traffic from people coming in to see the disaster.

An interesting side-bar mentioned in the DredgingToday.com article linked in the figure caption is that the dredging of the Code River has been hampered by the lack of heavy machinery.  However, people living near the river have been helping by manually carting material away.  Apparently it is well known that the volcanic mud is rich in nutrients, and a truck of this material is fetching 50-60 thousand Rp! (50,000 rupiahs convert to about $5.50 US.)