Category Archives: Landslide

Lateral Blast: The Mount St Helens eruption

Today is the 36th anniversary of the historic eruption of Mount St. Helens in Washington State, USA.

The May 18, 1980 eruption was a rare type of volcanic eruption known as a lateral blast. Most explosive volcanoes throw material upwards in an eruption; in the case of Mt. St. Helens the eruption occurred horizontally, releasing pent-up pressure inside the volcano. The eruption obliterated the entire north side of the volcano and resulted in the largest debris avalanche in recorded history.

eruption
An incredible series of images showing the explosive flank collapse in the eruption. Source: USGS

The 1980 Mt. St. Helens eruption played an extremely important role in improving our understanding of volcanic eruptions and the magma plumbing system beneath volcanoes. It was the first time pyroclastic flows – clouds of super hot gas, ash and rock that move at hundreds of miles per hour – were studied using modern scientific techniques. Even now, 36 years later, scientists are still publishing new and interesting insights gleamed from the 1980 and later eruptions.

Current_activity_USGS
The new central cone inside the older crater. Source: USGS

The volcano is still very much alive today. In recent decades a new volcanic cone has developed in the central crater. Thankfully, scientists from the United States Geological Survey (USGS) are keeping a close eye on the volcano and will hopefully provide warning if a new eruption is imminent.

See how Earth’s 1000+ active volcanoes were formed in this great national Geographic video.

 

More information:
[1] https://volcanoes.usgs.gov/volcanoes/st_helens
[2] https://pubs.usgs.gov/fs/2013/3014/fs2013-3014_text.pdf
[3] https://volcanoes.usgs.gov/observatories/cvo
The feature image at the top of the article was taken by astronaut Tim Peake from the International Space Station in 2016. Source Flickr

Advertisements

Newspaper archive helps enrich UK landslide database

by Faith Taylor

“The past is the key to the future” – and so creating accurate and thorough records of past events is a common goal for many working in natural hazards. Recording the recent history of some natural hazards is relatively straightforward where automatic instrumentation can be widely used – e.g., using a network of seismometers to record earthquakes across the world. Yet, recording when and where landslides have occurred is a bit of a pain…

The mess of rocks, mud, water and debris left behind on the ground in a landslide is the outcome of a set of processes (e.g., rainfall, ground shaking, erosion). So, to find a landslide, one must actively search for it across a landscape – e.g., by traipsing about in the field, or searching through aerial imagery. It can take teams of geomorphologists literally years of work to create a thorough inventory of landslides from aerial images.

landslide_papers
Old newspapers contain a wealth of information on the location of landslides and their impact on communities.

One common way to supplement records of landslides is to use human records, such as newspapers, photographs and diaries. Two excellent examples are (i) Dave Petley’s global fatal landslide database, which uses online news to record deaths caused by landslides, and (ii) the Italian AVI project has records of landslides going back hundreds of years from newspapers.

Yet when searching the literature, we noticed two things – firstly, people aren’t doing this for Great Britain and secondly, people weren’t really talking about how they searched the newspaper archives. I was lucky enough to receive a NERC-EPSRC internship to work with the British Geological Survey on searching the Nexis UK Digital Archive of regional newspapers to try and find articles about landslides.

The first step was experimenting to create a systematic search strategy to be sure that we were picking up as many articles about landslides, and as few articles about things like “landslide victories” as possible. Once this was settled, I applied our search to the Nexis UK archive (thank goodness this is digital and I didn’t have to flick through dusty old newspapers!) and started reading through the thousands of articles returned.

When I found an article about a landslide, I would try to extract as much information as possible, such as the timing, location, size and impact. I would then compare this to what was already in the BGS National Landslide Database to see if we were adding in more detail. To our surprise, this method was really effective and we increased the number of records in the database between 40% – 122% depending on the year examined. These additional records help us to better understand when, where and why landslides occur in Great Britain, and what kinds of impact they can cause.

Our Geomorphology Article is Open Access and available online at: http://www.sciencedirect.com/science/article/pii/S0169555X15300039

——————————————————————————————————-

Faith Taylor is a postdoctoral research scientist at Kings College London. Find out more about her work here. You can follow her on twitter @faithatron

Double warning time for volcanic lahars

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.

A recent Tungurahua at night. Source: Dr. Carlos Costales Terán, Wikimedia Commons
A recent Tungurahua eruption at night.
Source: Dr. Carlos Costales Terán, Wikimedia Commons

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.

An incoming lahar from mount Tungurahua. Source: IGEPN
An incoming lahar from mount Tungurahua.
Source: IGEPN

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.