The Bristol 'tsunami': Flood or fallacy?

This post was originally featured on http://betweenarock.co.uk/

30^th January 1607*.
The day dawns sunny and bright. You are ploughing a field in your smallholding deep in the Somerset Levels. As the sweat drips down your back, you hear a distant rumbling sound but think nothing of it; the wind has been blowing a gale all night. Suddenly, a shout from a neighbour makes you look up in alarm. At the end of the far field you see a great cloud hugging the ground, light dazzling off the whiteness. At first you are confused: is it fog, or smoke from a fire? But then you realise, it's water. Within ten seconds, the tumbling, roaring mass has advanced the length of the paddock. You try to run but it's too late. Knocked off your feet by the force of the wave, your head dips below the surface and you inhale a lungful of salty water...
^{*The exact date depends on whether you have a preference for the Julian or Gregorian calendar}

From eyewitness reports, this is what it felt like to be caught up in the most catastrophic flood ever to hit western Britain. Striking in January 1607*, its effects were felt all over the south-west of England, extending over 570 km of coastline from Barnstaple to south Wales and as far inland as Glastonbury (approximately 22km). Contemporary sources put the death toll at over 2,000, though modern estimates have revised this to 500 - 1000¹. The water flow is said to have been so fast "... that no gray-hounde could have escaped by running before them." But what was the cause?

Contemporary woodcut depicting the scene in Monmouthshire on 30th January 1607.

Prior to a modern-day brush with fame, the Bristol Channel Floods were variously attributed an extreme spring tide (the maximum extent of a tidal range that occurs when the Earth, Moon and Sun are in alignment, roughly every fortnight), a storm surge (high water levels associated with a low pressure weather system) or a combination of both. This type of coastal flooding is relatively common in the UK; a particularly deadly occurrence in 1953 killed 307 people in East Anglia.

The tsunami hypothesis was first proposed in 2002 by two academics (Haslett & Bryant - see references 2,3 and 4), and followed up in a series of subsequent papers by the same authors. Their re-interpretation of the events unintentionally coincided with the devastating Boxing Day tsunami of 2004, and so was perfectly poised to percolate the national consciousness. Numerous media articles publicised the theory, and the floods were featured in two BBC2 TV programmes (Timewatch - "The Killer Wave of 1607" and "Britain's Forgotten Floods").

Flood plaque in Goldcliff parish church, Newport. Reads "1606. On the XX day of January even as it cames to pass it pleased God the flud did flow to the edge of this same bras [brass], and in this parish theare was lost 5000 and od pownds besides xxii [22] people was in this parrish drown.". Photo credit: Robin Drayton.

Of course, publicity is not the mark of whether a theory is right or wrong, but proving this particular watery dispute one way or the other has been hindered by a couple of confounding conundrums: the subjectivity of historical sources and the ambiguous nature of tsunami deposits.

At the turn of the 17^th century, literacy levels in the UK were still relatively low. There were no newspapers (or Twitter!), thus first-hand accounts are mostly limited to privately printed pamphlets which tend to offer contrasting reports. For example, the weather on the day in question is conflictingly described as being "most fayrely and brightly spred", "tempestuously moved by the windes" and in the grip of "a mightie storm". The most supportive evidence for a tsunami comes from "Gods [sic] warning to the people of England" , a publication funded by the Church. Its coverage of the event is predictably zealous, describing the flood as a "universal, punishment by Water."
As geologists, the obvious solution would be to look to the rock record; however, tsunami deposits are notoriously tricky to identify because their physical markers are incredibly hard to distinguish from other sources of coastal flooding. Pro-tsunami authors Haslett & Bryantt cite sand "storm" layers in sediments, erosion of salt marshes, vortex pools, and imbricated boulder dumps as supporting evidence for a 'killer wave'; all features imply rapid deposition from a forceful flow of water. Their proposed mechanism for the tsunami is either a submarine landslide or earthquake in the sea between Ireland and Cornwall.

Prof. Simon Haslett atop imbricated boulders in the Severn Estuary. Photo was taken during filming of the BBC2 programme “The Killer Wave”. Source: http://profsimonhaslett.blogspot.co.uk

Perhaps the most compelling evidence against the tsunami hypothesis is that severe flooding in Norfolk is documented on the same day. Most tsunami models agree that it is geometrically impossible for the effects of a tsunami to wrap around the entire coast of England. It seems like the most plausible cause of the floods is a storm surge imposed on an unusually high spring tide. Indeed, the Severn Estuary has the second highest tidal range in the world. The contemporary reports of windstorms driving up the seas is reminiscent of storm surges in New Orléans during Hurricane Katrina in 2005.

Regardless of the cause, it is important to consider the impact that a repeat of the 1607 floods would have today, in order to mitigate against future disasters. The Severn estuary is home to the (active) Hinkley Point and (closed) Oldbury nuclear power stations, and is the proposed site of the controversial Severn Tidal Barrage. Other notable infrastructure includes two motorway bridges, a working port (Avonmouth) and half a million people living in Bristol alone! One risk assessment puts the cost of such an event at £7 - 13 billion¹.

In the wake of the 2004 Boxing Day tsunami, the UK government recognised they did not have a quantitative assessment of threat to the UK. This was despite another infamous tsunami study⁵ (the results of which are now viewed with scepticism) which predicted that a landslide off La Palma would generate waves "higher than Nelson's column" and smash into the west coast of Britain - mass media loved it. Happily for us, the government reports conclude "tsunami-type events [affecting the UK] are unlikely to exceed those anticipated for major storm surges", and "all major centres of development on coasts and estuaries have defences that have been designed to withstand such surge waves."

Should we have these in Bristol City Centre?

Despite their assurances, a small part of me feels pretty smug about a living and working a good 50 metres above sea level!

Charly Stamper

References
[1] "1607 Bristol Channel Floods: A 400-Year Retrospective" - Online publication by Risk Management Solutions.
[2] Bryant EA & Haslett SK (2007) Catastrophic Wave Erosion, Bristol Channel, United Kingson: Impact of Tsunami? The Journal of Geology: 115, p. 253-269.
[3] Bryant EA & Haslett SK (2002) Was the AD 1607 coastal flooding event in the Severn Estuary and Bristol Channel (UK) due to a tsunami? Archaeology in the Severn Estuary. 13: 163 - 167.
[4] Haslett & Bryant (2004) The AD 1607 coastal flood in the Bristol Channel and Severn Estuary: historical records from Devon and Cornwall (UK). Archaeology in the Severn Estuary. 13: 81 - 89.
[5] Ward, SN & Day, SJ (2001) Cumbre Vieja Volcano; potential collapse and tsunami at La Palma, Canary Islands. Geophys. Res. Lett. 28-17, 3397-3400.

The building stones of Clifton - a walking trail

 Building Stones of Clifton - A Walking Trail

 A thirty-minute ramble through 350 million years of geological time  

The trail includes five stops within Clifton and is approximately 1.5km long (blue trail).
Optional sixth stop is an additional 1 km (pink trail). Begin at Clifton Hill House, Lower Clifton Hill, BS8 1BX.

Bedrock geology

Bedrock geology of Clifton

The oldest rocks beneath Clifton are Devonian Old Red Sandstone, lower Carboniferous limestones and sandstones, and Upper Carboniferous Coal Measures. These are sediments deposited during a long period of fluctuating sea level. In the Permian period, formation of the supercontinent Pangaea caused uplift of existing landmasses which were consequently subject to strong erosional forces. The resulting detritus created the next generation of bedrock, and so the older sediments are unconformably overlain by Triassic conglomerates and sandstones, and Rhaetic limestones.

Site 1 - Clifton Hill House 

Bath Stone (oolitic limestone) - Jurassic
Start the trail at Clifton Hill House at the top of Lower Clifton Hill 

Clifton Hill House - Jurassic oolitic limestone

Built in the 1740s, this former merchant’s mansion is now part of a hall of residence for the University of Bristol. The front of the building is faced with cream-coloured oolitic limestone, a rock not native to Clifton; it was extensively quarried in (and is eponymous to) Bath when it became fashionable in the 18th century. Bath Stone was deposited in a tropical shallow marine environment, similar to that of the Bahamas today. The rock comprises millimetre-sized ‘ooids’, small lithic grains coated in concentric rings of aragonite (preserved as calcite) mud. Other features, such as cross-bedding and calcite veining, are neatly captured in the end stone.

 

Site 2 - Goldney House

Brandon Hill Grit - Upper Carboniferous

Continue Clifton Hill and cross the road at Constitution Hill [150m] 

 

Goldney House coach house - Brandon Hill Grit

Goldney House is also part of a university hall of resi- dence, although the main building is a modern addition to the early 18th century coach house and other outbuildings. The coach house wall is accessible from the pavement and is an irregular patchwork of Brandon Hill Grit, a coarse Upper Carboniferous quartzite sourced from nearby Brandon Hill. The rock was laid down as a deltaic sand coevally to the limestones of the Avon Gorge; coarser horizons in some blocks are evidence for ephemeral stream channels. Its distinctive pink-red colouration is staining from the overlying Triassic sediments. 

Site 3 - Caledonia Place
Pennant Sandstone - Upper Carboniferous
Continue on Lower Clifton Hill as it becomes Regent Street. Walk into Clifton Village and turn left along Royal York Crescent. To the south is Dundry Hill [600m]. Walk all the way along the terrace, turn right at the end into Wellington Terrace, and then second right into Caledonia Place [500m].

Caledonia Place - Pennant Sandstone mounting blocks

Though prevalent as a building stone in the city centre of Bristol, Pennant Sandstone is not as common in Clifton. This grey-coloured sandstone is rich in feldspar and micas, and was deposited in shallow waters in the Coal Measures. The poor cementation between individual grains made the sandstone easy to quarry; however, this is counterbalanced by its relative fragility and vulnerability to weathering. In Caledonia Place it has been employed as mounting blocks (to aid Victorian residents’ ascent into horse-drawn carriages). 

Site 4 - Clifton Suspension Bridge
New Red Sandstone - Triassic
Retrace your steps out of Caledonia Place and continue along Wellington Terrace, then Sion Hill [300m] 
 

New Red Sandstone facings at the Clifton Suspension Bridge

Clifton Suspension Bridge is Bristol’s most iconic land- mark and was designed by Isambard Kingdom Brunel in 1831 (but completed posthumously in 1864) to span the chasm between the Carboniferous limestone cliffs of the Avon Gorge. The base of the gothic towers are attractively faced with New Red Sandstone. Its distinctive red colouration reveals its subaerial formation in the deserts of Pangaea and layering from ancient sand dunes is preserved as cross-bedding.

 

Site 5 - The Observatory

Carboniferous Limestone - Lower Carboniferous

Follow the short footpath up the hill from the Bristol-side toll booth [200m] 

 

The Observatory - Carboniferous Limestone

Originally built as a mill in the late 18th century, Observatory Tower was purchased over fifty years later by a local artist who installed a telescope and camera obscura (to project panoramic exterior views onto a screen). The rounded rubble walls comprise fossiliferous blocks of Carboniferous Limestone hued from the gorge, and provide a reminder of a time when the Avon region was submerged beneath a balmy tropical ocean. Descend to ‘Giant’s Cave’ beneath The Observatory to further explore the strata of the Gorge. 

Site 6 [optional] - The Cumberland Basin

Cornish granite - Lower Permian

For a longer addition to your excursion, retrace your steps towards the Avon Gorge Hotel and take the Zig Zag footpath down to The Portway. Turn left and walk towards Bristol City Centre. Take care when crossing the busy road - it is best to walk over the pedestrian footbridge which begins in Granby Hill [∼1km]. 

 

Cumberland Basin - Bodmin Granite

The Cumberland Basin was excavated in 1809 when the River Avon was diverted to form a floating harbour and granite is used as capping material on the channel walls. Petrolographic analysis has shown it to be Bodmin Granite, part of the Cornubian batholith that is exposed throughout Cornwall and the Channel Island. This igneous rock formed a result of a huge mass of magma intruding into the crust during Variscan orogeny (∼275Ma). Though the surface has weathered to a smooth finish, individual crystals of grey quartz, white plagioclase and pinky- orange orthoclase feldspars, and dark-coloured biotite mica can still be identified. 

Charly Stamper 

References

- Jones D (1992) A History of Clifton. Phillimore, Chichester.
- Mowl T (1991) To build the second city: Arcitects and craftsmen of Georgian Bristol. Redcliffe Press Ltd, UK.
- Savage RJG (1988) Buildling Stones of Clifton. Proceedings of the Bristol Naturalists’ Society, 48: 85-104.

The Geology Collection University of Bristol goes OnLine

The School of Earth Sciences at the University of Bristol holds a collection of over 100,000 mineralogical, paleaontological and petrological specimens which were donated to the School over the past 100 years. Some iconic specimens are an original map by William Smith, a near complete and mounted skeleton of a sabre-toothed cat, fossilised bones of early dinosaurs and an array of minerals from now inaccessible mines in the UK. The collection also contains over 1500 type fossils and published specimens, a unique and valuable resource to researchers worldwide.

Rhodochrosite from Argentina (BRSUG B2502)

 

Over the past decade efforts have been made to record and document the collection to unlock its scientific and educational potential. The current digitisation project OnLine aims to improve remote access to the wealth of geological specimens in the collection. The project includes the design of a brand new website as well as the development of an extensive photo archive and a searchable online database.

A taster of the future website of the Geology Collection University of Bristol, going live in autumn 2012.



Claudia Hildebrandt, Collections Manager: "With the valuable help of students and volunteers we have now digitise over 60,000 specimen records for online publication. We collected details from registers, card catalogues, collectors’ field notebooks and the specimens themselves and merged all information into a comprehensive database. Additional funding from JISC (as part of the BRICOLAGE project) allowed us to employ a student who reorganised taxonomic, stratigraphic and geographic entries and ensured consistency across the whole database.”

“We have also started to add recently taken photographs of specimens to the database. This will offer users a look behind the scenes of our stores.”

Volunteer Charlie Navarro editing photographs of Cretaceous chalk fossils.

Once the website goes live in autumn 2012 the OnLine project will enter its second phase.

Claudia: “We aim to create links between specimens and relevant scientific publications and publish a tool that visualises the geographic distribution of all our UK specimens. We will also add a feedback function to the catalogue which will allow amateurs and specialists to comment on specimens and send enquiries.”

"And this is just the beginning. Parts of the collection need to be revisited to update taxonomic and stratigraphic information. We also plan to highlight the historic value of our collection. Many honorable and well know geologists donated their samples to the Geology Collection, from local fossil collectors to internationally known palaeontologist. We would like to dig deeper and reveal the people behind our collection and the extraordinary journeys some of our specimens have been on.”

If you would like to find out more about the Geology Collection follow us on Facebook.

Claudia Hildebrandt

Nailsea Environmental & Archaeological Team – NEAT

Nailsea Environmental & Archaeological Team

NEAT - Aims and Objectives

Nailsea Environmental & Archaeological Team – NEAT, was set up in September 2004 to undertake archaeological research in the Nailsea area, including Tickenham, Wraxall, Backwell, Chelvey and Brockley.

     Our aim is to carry out fieldwork to find new archaeological sites, record existing sites and to augment the North Somerset Historical Environment Record, in conjunction with the County Archaeologist. 

     The methods used include land survey, geophysical survey, map regression and reference to local archives and involve work with other similar groups in North Somerset. 

     In addition, NEAT has carried out a survey of dry stone walls in Nailsea, recorded the age of buildings and recorded the hedges in the area. There is research ongoing into other aspects of our local environment. 

     During 2011 NEAT established a geology group with the initial aim of establishing ‘geotrails’ around the area to show and explain the local geology. It is intended to complete the geotrails project and publish a guidebook in 2012.

     There is a live link to the NEAT web site in the right hand column on this blog home page.

David Sowdon

Inspiring the next generation

Kate Hibbert, University of Bristol

Guest blogger Kate Hibbert is a PhD student in Earth Sciences at the University of Bristol. She is also a STEM ambassador and is interested in how academics can inspire the next generation of scientists.

 

Postgraduate students at the University of Bristol are heavily involved with outreach teaching activities, visiting Bristol schools to talk about various topics in Earth Sciences. Volunteers are co-ordinated by the STEM ambassador scheme. The aim of the scheme is to get more young people involved with STEM subjects (Science, Technology, Engineering and Maths) and it effectively acts as a matchmaker between schools and willing expert volunteers. The network includes professionals as well as university students. STEM ambassadors go in to schools and might, for example, run a workshop, provide mentoring for a small group, talk to an after school club or take part in a careers fair.

Bristol students have been involved in several projects, including the Bristol Dinosaur Project. Thousands of school children of all ages have had a visit from the Dinosaur Project team, giving them the opportunity to learn about this dinosaur unique to the Bristol region in an interactive workshop. The session also involves a life-sized jigsaw of the Bristol dinosaur and handling real fossil specimens, an activity that never fails to spark the imagination.

Primary school children getting some hands-on experience of life as a palaeontologist. Photo credit: Bristol Dinosaur Project

But it’s not just dinosaurs that can inspire children – workshops run by Bristol Earth Sciences PhD students have covered a wide range of topics, from the rock cycle to volcanoes to meteorites. A workshop might involve handling rock specimens, squashing plasticine to learn how a metamorphic rock is made, or using the classroom to reconstruct the scale of the solar system.

Teaching the rock cycle using crayons. Photo credit: http://mesmrswhitesclass.blogspot.co.uk

The benefits of these school visits are not limited to imparting knowledge about the topic covered, but also come from allowing children to meet ‘real-life scientists’, helping to break down some of the stuffy scientific stereotypes and encourage more people into science subjects and science careers. The rewards for volunteers are great, not least giving confidence in public speaking. If you can successfully hold the attention of a classroom of 10 year-olds, then giving a professional presentation seems significantly less daunting! 

Three lots of fossil finds for local school children. Photo credit: Bristol Dinosaur Project

Kate Hibbert

Links:

If you’re interested in the STEM ambassador scheme or want to arrange for an ambassador to visit your school: http://www.stemnet.org.uk/content/stem-ambassadors

A previous blog post about the Bristol Dinosaur: http://avonrigsoutcrop.blogspot.co.uk/2012/02/bristol-dinosaur-project.html

A journey to the centre of the Earth (in BS8)

Bristol Experimental Earth STudies (BEEST) is one of seven research groups in the Earth Sciences department at the University of Bristol. Its primary activities involve conducting experiments to probe deep into the Earth’s interior. The BEEST labs consist of a series of experimental apparata that are capable of replicating the conditions at which igneous rocks are created, from lava flows at the surface down to the core-mantle boundary and everything in between. Experiments can either be conducted on natural rocks or synthetic mixes of chemicals. The latter option has the advantage of allowing us to simplify complex natural systems and control the amount of volatiles (such as CO2 and H2O) in the sample.

• Lava flows = 1 atmosphere furnace: This is in effect a gloried oven, though it is a little hotter than you might use for your Sunday roast! Samples are lowered on a wire into the hotspot of the furnace via a vertical pipe and are heated to temperatures of up to 1700ºC at room pressure and atmospheric conditions. It is primarily used for studying the changes in mineralogy of lava erupted onto the Earth’s surface.

 

Lava flows can be costly volcanic hazards, destroying property and agricultural land; however, certain types of lava can be economic assets. Dr Richard Brooker is using a 1 atmosphere furnace to look at the properties of kimberlites, lavas that are famous for their propensity to carry diamonds.

• Shallow magma chambers = cold seal pressure vessel: This piece of equipment allows us to simulate conditions where magma is stored beneath active volcanoes. Samples are enclosed in small metal capsules and inserted into a metal tube, called a bomb. The bomb is then flooded with water which creates a pressure on the capsule corresponding to being at a depth of 1-6km below the surface of the Earth. Finally, temperatures are elevated to ≤900ºC using an electric current. The decrease of pressure and temperature can be controlled such that we can accurately simulate the eruption of a volcano.

 

A cold seal pressure vessel being operated by Bristol PhD student, Jenny Riker. Jenny is investigating how decompression drives crystallisation in erupting magma at Mt St Helens (pictured left).

• Lower crust and mantle = piston cylinder and multi-anvil apparatus: As we descend deeper into the Earth, the amount of pressure we need to apply to a sample increases dramatically. These two pieces of equipment do this by squeezing the metal capsule between differently shaped blocks of metal; however, the greater the pressure needed, the smaller the sample must be. The capsules used are typically <5mm in length and must be analysed using high magnification electron microscopy. The piston cylinder can simulate up to 120km depth and 1400ºC; this makes it an excellent device for studying how magmas are generated in subduction zones. The multi-anvil can probe much deeper, up to the core-mantle boundary, and is used to investigate the state of the Earth’s molten mantle.

The piston cylinder apparatus can be used to simulate conditions where magma is generated at island arcs: pressure is applied manually using a lever. PhD student Charly Stamper is conducting experiments at lower crustal depths to gain insights into the magma chamber beneath Grenada, Lesser Antilles.

 

Carbonatites are carbonate-rich igneous rocks. Oldoinyo Lengai in Tanzania (above left) is currently the world's only active carbonatite volcano although pyroclastic carbonatite deposits have also been discovered in Europe. Sorcha McMahon's PhD is focussed on how these strange magmas form, using the multi-anvil apparatus (above right). High pressures are achieved placing samples within an octahedral ceramic pressure cell, at the centre of 8 carbide cubes (see inset).

• Core = diamond anvil cell (DAC): In order to replicate conditions at the centre of the Earth, we need to employ the hardest substance known to man-kind, diamond. The most astonishing aspect of this equipment is that the DAC is small enough to fit into the palm of your hand! Sample powder is placed between two diamond tips and heated using a laser. The samples are so small that analysis must be carried out at a synchrotron, such as CERN, using the high-energy x-rays generated by particle acceleration. Applications of this technique include testing the hypothesis that the Earth’s iron core contains small amounts of a light element, such a carbon or silicon.

A diamond anvil cell (DAC) can replicate the pressures and temperatures found deep within the Earth. Andrew Thomson and others at Bristol are using a DAC to study the chemistry of the Earth’s core.

All this equipment can be found in three rooms in the basement of the Wills Memorial Building. It just goes to show you can take a journey to the centre of the Earth without leaving Bristol!

For more information:

BEEST research group - http://www.gly.bris.ac.uk/research/groups/BEEST/Site/index.html

Department of Earth Sciences at the University of Bristol - http://www.gly.bris.ac.uk

Charly Stamper, BEEST PhD student

This post also appears in http://bristoluniversityfacultyofscience.blogspot.com - University of Bristol Science Faculty blog