Tuesday, 21 May 2019

Hot off the press! Results from our Coastal Landslide Observatory // by Catherine Pennington

Landslides experts at the British Geological Survey are excited to have finally published results from a project they have been working on for nearly twenty years. Cath Pennington tells us all about it…

BGS Landslides Team at their Coastal Landslide Observatory nr Aldbrough, East Riding of Yorkshire. Left to right: Cath Pennington, Pete Hobbs, Matt Kirkham, Simon Holyoake, Nikhil Nedumpallile Vasu, Lee Jones
The team at the Coastal Landslide Observatory nr Aldbrough,
East Riding of Yorkshire. Left to right: Cath Pennington, Pete Hobbs,
Matt Kirkham, Simon Holyoake, Nikhil Nedumpallile Vasu, Lee Jones.
On a windswept, wave-battered cliff on the coastline of the East Riding of Yorkshire stands an unassuming landslide that has no idea just how important it is. This landslide is being watched.  Every move it makes is being recorded and analysed by us here at the BGS.

This is our first Coastal Landslide Observatory, where we have been collecting data for the last 18 years. This long term monitoring has allowed us to capture and record how the ground behaves through cycles of deep-seated landslide activity.

Today, this work has been published in two papers in the Quarterly Journal of Engineering Geology and Hydrogeology:

Establishment of a coastal landslide observatory at Aldbrough, East Riding of Yorkshire

Coastal landslide monitoring at Aldbrough, East Riding of Yorkshire, UK *OPEN ACCESS*

Why do we need a Coastal Landslide Observatory?

We know much of England’s southern and eastern coastline is eroding. In some places, this is happening more quickly than in others. In fact, the Landslide Observatory is part of the 50 km-long Holderness coast, which is one of the most rapidly eroding coastlines in Europe. Add sea level rise and climate change predictions of bigger and more frequent storms into the mix and it is clear that we need to be prepared so we can be resilient.

The BGS Coastal Landslide Observatory near Aldbrough, East Riding of Yorkshire
The BGS Coastal Landslide Observatory near Aldbrough, East Riding of Yorkshire

We need to understand how the coast behaves so we can forecast what is likely to happen in the future and the rapid rate of erosion at our Aldbrough CLO provides a good opportunity for studying landslide processes.  For example, in order to develop and position early warning systems we need to understand how far inland there is a measurable response of the ground to the coastal landsliding. Communities affected, policy makers, local government and national agencies need to know how to manage coastal change as we cannot, and indeed should not, protect the entire coastline with hard engineered defences.  
Matt Kirkham, Geotechnical Soils Lab Specialist,  carrying out Terrestrial LiDAR survey at the  Coastal Landslide Observatory,  Aldbrough, East Riding of Yorkshire
Matt Kirkham, Geotechnical Soils Lab Specialist,
carrying out a Terrestrial LiDAR survey at the
Coastal Landslide Observatory,
Aldbrough, East Riding of Yorkshire

People have been measuring the rate of coastal retreat for decades in the UK, longer even.  This started with highlighting changes in the cliff top on Ordnance Survey maps, aerial photograph comparisons and directly measuring changes with a tape measure.  These methods produce an estimate of general coastal retreat but this can only ever be linear e.g. 1.5 metres per year.  We do not know if the 1.5 metres happened little by little or suddenly all at once.  

Peter Hobbs, project manager for the CLO, explains: “What we want to understand is much more than just the general speed at which the cliff top is retreating. We want to know how the landslide behaves and what drives it”. So how have we done this?  

The Observatory

As well as geological and geotechnical tests and observations, we have used several techniques to monitor the landslide: 

Firstly, observational techniques include terrestrial LiDAR and UAV (drone) photogrammetry. Terrestrial LiDAR (pictured right and below) is a laser scanner which, when combined with highly accurate GPS, allows us to produce 3D models of the cliffs.  Lee Jones, project leader for geomatics explains: “Using several scans made at different times, we can calculate the amount of material lost from the cliffs (volume loss) and measure cliff top retreat.  We can also see how the landslide is changing and where”.

Lee Jones using the back-pack mounted Pegasus LiDAR
We were one of the first earth-science users of terrestrial LiDAR techniques in Britain and, over the duration of the monitoring period at the CLO, we have developed the technology and interpretation of data considerably.

The UAV enabled us to capture aerial photographs and fill in gaps and shadows where the ground-based LiDAR cannot access.

2001-2017 LiDAR scans showing the cliff retreating.  Only scans from alternate years are used here to simplify the image.
2001-2017 LiDAR scans showing the cliff retreating.  Only scans from alternate years are used here to simplify the image

Secondly, geotechnical monitoring. Three pairs of boreholes were drilled 20 m into the ground.  These were set 10 m, 20 m and 28 m back from the cliff edge. Piezometers and inclinometers were installed to measure changes continuously in pore water pressure and any physical movement of the boreholes. The idea is to observe any changes as, with time, the cliff effectively approaches the boreholes.   


The Aldbrough Coastal Landslide Observatory showing the instrumented borehole pairs, sited landward of the cliffs
The Aldbrough Coastal Landslide Observatory showing the instrumented borehole pairs, sited landward of the cliffs

Lastly, geophysical instrumentation was added.  This is PRIME (Proactive Infrastructure Monitoring and Evaluation) which is BGS’s automated electrical resistivity topography system. This measures changes and movements in water content and temperature and is live-streamed back to the office via the web.

We have also installed a weather station and get wave and storm data from a wave buoy just offshore.

Results

"We have measured the amount of cliff lost to the sea. This ranges from 1200 to 6300 m3 per 100 m section of cliff per year. That’s roughly 0.5 - 2.5 Olympic-sized swimming pools for every 100 m length of cliff, every year."
Using this range of monitoring techniques, we have been able to track changes in the cliff slope more accurately than previously possible. Preliminary results are:
  • We have measured and observed the primary landslide type as deep-seated rotational with secondary topples, rock fall and flows.  
  • We have found that landslide activity is cyclic, with major landslide events occurring every six to seven years.  This activity is unsurprisingly related storm frequency and wave energy but it is mostly driven by groundwater.  
  • The Dimlington Bed is key for rotational landsliding.  It is a soft silty clay that the overlying geology slides along.
  • We have measured the amount of cliff lost to the sea.  This ranges from 1200 to 6300 m3 per 100 m section of cliff per year.  That’s roughly 0.5 - 2.5 Olympic-sized swimming pools for every 100 m length of cliff, every year.
Peter Hobbs, happy with the recent
upgrade to the weather station

And the future…

Back to Peter Hobbs: “Long term monitoring is a huge commitment from everyone involved, without which this kind of science research would not be possible.  The only way to do this accurately is to commit to long term monitoring. We intend to continue our work at our current CLO and are considering other sites and other new technologies”.

We hope that this work will contribute not only to our understanding of landslide processes, but will also inform policies such as Shoreline Management Plans to help manage the coastal changes we will see in the future.

You can read more about this and our other landslide observatories here. Keep up-to-date with new developments on the BGS Landslides Team on Twitter. The team can be contacted here




Thursday, 16 May 2019

Homeward Bound: Last Leg of the ORCHESTRA Cruise (Part 4) // by Carol Arrowsmith

Carol Arrowsmith is a chief technician in the stable isotope facility at the BGS. She recently took part in an expedition to the Southern Ocean as part of  ORCHESTRA (Ocean Regulation of Climate by Heat and Carbon Sequestration and Transports), a NERC funded programme with partners at the British Antarctic Survey (lead), the National Oceanography CentrePlymouth Marine Laboratory, and many more including BGS. Here she updates us as she nears the end of her expedition on the RRS James Clark Ross…

Carol on board the RRS James Clark Ross near Signy Island
We were at sea for around 8 weeks on the RRS James Clark Ross, undertaking the ANDREXII transect. We set off from the Punta Arenas, Chile, calling in at the Falklands before crossing the Drake Passage to the tip of the Antarctic Peninsula at 60oS, and then out along over 3000 miles to the Indian Ocean at 30oE. 
King Penguins

Along this route we collected samples at 96 separate locations (stations), resulting in >1800 water samples for oxygen and carbon isotope analysis with help from my buddy, Margot Debyser from Edinburgh University and Ash Smith, the BAS Laboratory Manager. The samples will arrive back in the UK for analysis at the BGS in the summer for isotope analysis and will tell us about how much carbon the ocean has absorbed and how much fresh water has been added from melting of the ice caps. We also collected around 350 for radiocarbon C14 analysis which will be sent to the Woods Hole Institute, USA where we'll be able to shed light on the age of the water. These samples form part of the 5 year ORCHESTRA research programme to try to understand the structure of the Southern Ocean and, more importantly, what changes are taking place within the ocean due to human impact.

After we finished the last sampling in the Indian Ocean our ship steamed back to the South Orkney Islands and Signy. There were plenty of seals (fur, leopard and crabeater) dotted about the ice, most of them were used to seeing ships and didn’t bother to move when they saw us coming! In particular, we got to see the British Antarctic Survey base, which is now evacuated for winter, and moved some cargo around the holds in readiness for the journey home. We then sailed down to the ice sheet forming around the Antarctic Peninsula, where we held the end of cruise dinner: a BBQ on the ship's deck while it was snowing! 

The ship docked at Mare Harbour on the Falkland Islands, where we spent the day demobilizing, taking inventories of samples, packing up the equipment, and generally clearing up. We also had a flying visit to Volunteer Point to see King and Gentoo Penguins. The RRS James Clark Ross then left the Falklands for the first of 2 trips to Rothera Station to pick up scientists, crew, contractors and equipment to take them home.

Overall, it’s been a successful research cruise but I am glad to be back on land! I would like to thank PSO Andrew Meijers at BAS for his leadership and management. Also many thanks to the dedicated crew on board, engineers, deck crew and stewards who all played their part.
Some of the crew and scientists at the end of the cruise

ORCHESTRA is in the second year of a five year collection programme around the World’s oceans. Check out @CarolArrowshimth and @ORCHESTRAPROJ on Twitter, or on Facebook (Orchestra Project).






Tuesday, 14 May 2019

Latest Developments in Methane Isotope Analysis // by Andi Smith

Andi Smith is a Stable Isotope Geochemist at the BGS. Here he tells us about the facility's new Sercon GryoGas instrument, which was presented at the EGU General Assembly...


Andi presenting at EGU
Recent requirements for understanding methane formation processes has led to investment in a new stable isotope mass spectrometer by the BGS. This instrument is specifically designed to analyse both carbon and hydrogen isotopes in water and gas samples and is perfectly set up to support large groundwater and soil gas surveys. As part of the launch of this equipment the stable isotope team including Prof. Melanie Leng and Dr Andi Smith went and presented the new instrumentation at European General Assembly last month.

The Sercon CryoGas unit
The British Geological Survey has recently invested in a first of its kind, automated system for the analysis of methane isotopes (both C and H). This system was designed and built as part of a collaborative project between Sercon Ltd and members of staff at the National Environmental Isotope Facility, BGS Keyworth. The system is set up to undertake rapid throughput, high precision isotope measuments and is perfect for analysing the kind of baseline samples regularly collected by the BGS, as well offering a great new facility for the wider research community.

The system uses the Sercon CryoGas unit with a series of cryogenic and chemical traps, alongside gas chromatography columns to separate methane from other gasses, including major gases such as oxygen, CO2 and nitrogen. Once separated the methane is broken down into its component parts (carbon and hydrogen) and each can be analysed on the Sercon 2022 mass spectrometer for stable isotope composition. The automatic sampling unit means that between 21 and 250 samples can be run in an automated batch, drastically increasing sample throughput.  

Currently the system is being used to analyse carbon in methane and our first BGS soil survey samples will be analysed within the next few weeks. We also have the option to analyse carbon isotopes in CO2, so this instrument could be of wider interest to a number of groups within the BGS.

I am very excited to develop new applications and collaborations surrounding the isotope analysis of methane and CO2, so please free to contact me or come along and discuss your project ideas!

To find out more about the research in this post contact Dr Andi Smith or via Twitter @AndiSmith10.

EGU provides a great platform for sharing and discussing new research with scientists from around the world, holding workshops, attending short courses and training sessions, and meeting up with colleagues. To catch up with all the BGS activity at the conference check out #EGU19 and also be sure to take a look at the @BritGeoSurvey Twitter feed.