By Robert Jones
Real-time rainfall data can be used to potentially double warning times for rain-triggered lahars on the slopes of Tungurahua Volcano, compared existing ground-based detection methods.
Tungurahua volcano is located in the Eastern Cordillera of the Ecuadorian Andes and its current period of eruptive activity has been ongoing since 1999. This intermittent activity has resulted in the deposition of a lot of loose unconsolidated pyroclastic gravel, dust and ash on the slopes of the volcano.
During heavy rainfall, for which this region is renown, this loose material gets mixed into the rain water flowing off the volcano and results in extremely dangerous rain-triggered lahars, or volcanic mudflows. Think flash floods and giant rivers of mud and rock rolled into one.
The city of Baños lies approximately 8 km north of the summit of the volcano and is a very popular tourist destination, with its population increasing from approximately 18,000 to around 50,000 during holiday periods. The primary road linking Baños with the Pan-American Highway and other provincial cities crosses several lahar-prone drainages of Tungurahua and these flows pose a significant risk to infrastructure within these valleys.
Rain-triggered lahars have not caused any fatalities at Tungurahua but cars have been buried, road crossings inundated and the El Salado Baths (a popular visitor attraction) have nearly been inundated by flows in previous years.
The volcano is monitored from the Tungurahua Volcano Observatory (OVT), operated by the Instituto Geofisico, Escuela Politécnica Nacional (IGEPN). The primary methods of lahar monitoring are detection by Acoustic Flow Monitors (AFMs), which measure ground vibration as the flow passes and also flow identification by a community-based monitoring system consisting of a network of volunteers known as Vigias.
Analysis of both the rainfall and lahar record between March 2012 and June 2013 indicated that peak rainfall intensity can be a key indicator of a potential lahar occurrence. The peak rainfall intensity during a particularly rainy period is used along with previous knowledge of the amount of moisture already in the landscape to estimate the probability that a lahar will exceed a pre-defined flow size. This method was tested using the July-December 2013 lahar and rainfall records and not only did our probabilities effectively predict the occurrence of lahars, but peak estimated lahar probability was consistently reached prior to lahar detection by the Acoustic Flow Monitor network. This probabilistic analysis produced an average of 24 additional minutes of warning time during the test-period.
Read the full paper at: http://link.springer.com/article/10.1007%2Fs00445-015-0946-7
Robert Jones is a PhD research student in the School of Earth and Environment at the University of Leeds.
Here’s an example from Ubinas volcano in neighbouring Peru, of the force and destructive power of lahars.