Sunday, 16 October 2016

Geophysics at the Gorgan Wall, Iran

Hunting the Red Snake – part II

Back in Iran, this time with my brother, Martin, to continue the hunt for the remainder of the Gorgan Wall.  Last year I was here with marine geophysical equipment to try and find the remains of both the Gorgan Wall and the Tammisheh Wall as they enter the Caspian Sea as part of a project with the University of Edinburgh and the National Museum, Iran.  From a previous blog (GorganWall I) I showed the results for the Tammisheh Wall extending well over 2km from the southern shores of the Caspian into a large lagoon behind the Miyankale Peninsula.  The sidescan sonar survey and sub-bottom profiling showed the remains of the brick wall with its accompanying ditch/canal.  Unfortunately we so no manifestation of the Gorgan Wall extension – so back to try again.

The Gorgan wall projection to the west towards the Caspian Sea
The Gorgan Wall (the Red Snake) extends from the Alborz Mountains in the east across the Gorgan Plains and was built from the 4th C AD as a defensive structure to keep out the marauding Turks from the north.  The wall was constructed of bricks fired from local clay in kilns spaced 40-80m apart along the length of the wall. It was at least 2m wide and tall expanding to a more substantial feature at numerous towers and where defensive forts occurred.  In front, to the north, of the wall was a 10-30m wide, up to 3m deep, canal.  The remains of the wall and canal are relatively well documented to the east. H,owever to the west, evidence of it remains elusive with historical writings describing the wall splitting into different parts and extending down to long-lost towns.

Despite being of similar age to the Tammisheh wall and being relatively close to each other the geomorphological setting for both is somewhat different.  The Tammisheh wall extends into the Caspian at a place where the sea is relatively sheltered with fairly benign sedimentation gently silting up the almost closed lagoon.  The projection of the Gorgan Wall however is across an area of coast where there have been highly dynamic changes due to the interplay between the Gorgan Ricer discharge and longshore drift bringing sediment onshore from the Caspian.  The present day shoreline demonstrates these active processes where the waves can reach impressive magnitudes due to a fetch stretching the length of the Caspian.

CMD Mini-explorer and Explorer ground conductivity meters
This year we have returned to attack the challenge of finding the remaining western part of the Gorgan wall as it progresses towards the Caspian Sea. We come armed with electromagnetic instruments, the GFInstruments CMD Explorer and Min-explorer.  Both are frequency domain ground conductivity meters, each with three coil spacings, in order to look to a range of depths.  We have a Leica dGPS for positioning control and for ground truth work a more traditional shovel and trowel.

The western limit of the wall is manifest by a series of “robber” pits that were used by locals to mine the decaying bricks for use in other projects.  The wall and remains of the canal that ran along the north side of the wall run in a straight course here for at least 20km.  Our first geophysical grids were laid over the robber pits and known wall/ditch locations in order to characterise their geophysical signature. The figure below shows this mapped on the satellite images.  Note that the background satellite images clearly define the agricultural system of 200x200m fields and also parts of the old natural landscape with its river channels and back barrier bars with sloughs.
EM Conductivity over robbed-out portion of wall
We continued to map the wall to the west and after approximately 1km a large modern drainage ditch was encountered and gave us the opportunity to ground truth the geophysics.  A 2D interpretation of the geophysics together with the surface mapping suggested that wall and ditch might exist here.  Excavation proved this to be true and samples have now been taken for analysis.

Using this characteristic signature mapping was continued a further 5km to the west with a complex pattern developing of linear features mixed with sinuous features.  Our current thinking has an interpretation based on a landscape evolution of shorelines behind which the old Gorgan River fights its way to the sea and through which the wall and canal/ditch is cut.  It is likely that the dynamic natural landscape was always an issue for maintaining the wall and canal here and a much larger geophysical and ground truth investigation is going to be necessary before a clearer picture of the history is revealed.
New geophysical results showing extension to the west from last known position

So, more geophysics to come hopefully in 2017. 

During the trip we also tried making maps with and AUV operated by Georgian colleagues.  While the purpose was to make maps along the wall projection we also took time to investigate some of the more interesting geological features.
Dormant mud volcano,Gorgan, Iran

This was way too short a trip as usual but a highly enjoyable one.  Our biggest issue this time was getting the equipment through customs – lessons for the next trip.  Our biggest hazard encountered (apart from the driving)  ........... watch out for those camels!







  

Monday, 30 May 2016

AUV hits Orkney

In the week of large scale remembrances of the Battle of Jutland that will include amassing parts of the British Naval Fleet, the German Fleet and possibly parts of the Danish fleet we made our own bit of history by testing for the first time one of the new generation of survey vehicles the Gavia AUV in the waters of Orkney.  The Gavia (Teledyn, Iceland) Autonomous Underwater Vehicle is a type of propelled platform designed to deploy geophysical instruments for survey beneath sea.  The vehicle looks like a small torpedo and in our configuration has onboard a complex navigation system, sidescan-bathymetric sonar and a high resolution camera.  The sonar is used to map the seafloor and to obtain backscatter images of the features on the seafloor.  The camera can likewise be used to identify seafloor features and to mosaic complete maps of what is there. There are two big advantages of using AUVs over conventional surface-based survey methods.  The first is that by flying an AUV beneath the surface it will not be affected by the noise and motion of waves and thus be able to “fly” in a steadier manner.  The second is that it can be pre-programmed for the survey and launched from either a boat or the shore.  With a forward looking sonar onbaord for collision avoidance the AUV does all the work while you sit back and have a cup of coffee – at least that is what should happen in theory!


The AUV (named “Freya”) was brought to the site by a team from the Scottish Association for Marine Science out of Dunstaffnage (SAMS) and was part of a small grant awarded to us by the Marine Alliance for Science and Technology Scotland (MASTS).  For John Howe, Karen Wilson and Colin Abernethy it was a first for not only visiting Orkney but also for using the AUV on an archaeological project.   Time was split between surveying the loch of Harray, near to the Ring of Brodgar and Ness of Brodgar archaeological sites and surveying in the Bay of Firth close to areas where we have previously mapped and reported unusual features on the sea floor.


Context
The Rising Tides project has been investigating the area around the Ring of Brodgar for a number of years.  Most recently we have completed a full bathymetry and sub-bottom sonar survey of the loch of Stenness to the west.  The purpose of this work was to reconstruct the palaeo-landscapes and environments when the Ring of Brodgar and Ness of Brodgar were being built and used. What our work demonstrates is that the loch was smaller at that time and further that there was a complex history of sealevel rise associated with the infilling of sediments with a step change in sediment input coincident with changes in vegetation in the catchment at about 6ka BP. For more details on this see our publication “The environmentalcontext of the Neolithic monuments on the Brodgar Isthmus, Mainland, Orkney

Caroline and I have also been experimenting with digital reconstructions for the area that can be seen on our test site "Ancient Lands

AUV in the Loch of Harray
In order to match the work in the loch of Stenness we brought the AUV to the loch of Harray.  This loch is a shallow, freshwater loch to the east of the Brodgar isthmus.  Previous surveying with the sub-bottom profiler showed it to not only very shallow at the southern end (less than 4m water depth), but also that the sediments were gas saturated for the most part.  Because of the very shallow water the AUV was not able to “fly” beneath the water and had to be operated as a surface vehicle.  This, combined with the fresh water challenged both the vehicle and the operations team to come up with novel ways of ensuring the AUV did not either crash into the bottom or into any of the small fishing vessels on site! Unfortunately, the weather also proved problematic with strong winds.  The vehicle was able to survey a few lines of data but the automated tracking features did not work correctly and so the vehicle did not manage to stay on course in order to survey a complete grid of data.

AUV in Bay of Firth
Following the tests in Harray (also useful because it was a confined loch and so there was no chance of the AUV being lost out to sea!) we took Freya to the Bay of Firth.  Here she was much more at home back in saltwater and also with a greater depth range to work in (up to 9m water depth).  A survey grid was programmed in the centre of the bay over areas where we have previously recorded and dived on unusual stone features.  Freya was deployed from a small rib and perfectly performed her planned mission of bathymetry mapping, sidescan sonar imaging and photography.  The preliminary results, processed within minutes of return to shore (another huge advantage over old methods of survey) showed a resolution that we had not seen before.  Fantastic new images of the seafloor which we will now ponder over before our return to dive on them in August.  Look out for results in a later post.
The AUV opens up a new era for us with archaeological survey.  There are so many sites that could benefit from this type of survey and many new and exciting discoveries to be made.
The AUV team with Richard and Caroline in Orkney - check out the renewable power sources!

 PS – on a historic note, the Gavia is approximately half the size (half the length and diameter) of the original WW I torpedoes and weighs about the same as the explosive head that these carried

Friday, 11 March 2016

Recon on Lewis

Recon Survey to the Outer Hebrides

to see this in 3D go to GoogleSpheres here

Over the last 10yrs or so I have made a number of visits to the Outer Hebrides for both work and holidays. Most of the research trips have focused on marine biological habitat mapping and assessment of the impacts of storm activity on the coast lines. However, as with most of the Scottish landscape, the archaeology of the islands tells a compelling story, especially in comparison to the work we are currently doing up in Orkney.  So when Donald Herd, a colleague and native of Lewis, mentioned the possibility of a trip to visit his ancestral stomping grounds with the possibility of building collaborations for some future work on the islands I readily agreed to go even if it is sometimes dodgy weather in March!

Donald hails from the village of Suainebost in the far north of Lewis where there is a fantastic community historical society – Comunn Eachdraidh Nis.  This group is working to preserve island history, language and culture for both local community now and in the future as well as providing a resource for visitors to the area. This north part of the island has a diverse range of heritage on offer from some of our most ancient rocks in the Lewisian Gneiss to the heritage of the people. A great example of this is the recently completed investigations published in two books by Chris and Rachel Barrowman on the archaeology and heritage of Ness and an investigation on the unusual 16C-17C remains on the sea stack of Dun Eistean.  Hopefully we will be able to find funding to work on some of this in the future.  

The island of Lewis is justifiably famous for its archaeology, the centre piece of which are the iconic standing stones of Calanais (Callanish).  The best estimate of when the stones at Calanais were raised is about 3000BC, nearly at the time that farming began during the Neolithic here. However it is incredibly difficult to date the actual erection of stone circles, especially when almost no other structures, either houses or burial chambers have been discovered in the surrounding environment. We visited this site in order to check out the wider landscape as a potential place to conduct palaeo-landscape studies.  Since it was a quiet time of year with no visitors, Donald also took the opportunity to fly the site for aerial photography.  The results were quite stunning and fit nicely into the quick 360 image that we took at the centre.

We experimented with photographing a number of the stones as the structure displayed in the Lewisian Gneiss that the Neolithic people used is quite stunning!


As the day was such a good one we visited a much later broch on our way back to the north of the island.  Dun Carloway is a remarkably well preserved Iron Age broch (a type of fortification found throughout Scotland) likely constructed between 100BC to 100AD. It is of typical double wall construction which can be seen in the east side. The remains were in use, laterally as a kiln until at least 1000AD.  Folklaw has it that the clan Morrisons of Ness (Donald’s ancestors) used to hide in it while they went on cattle raids of their rival clan, the MacAulays! 

Now looking forward to a trip back, if for no other reason than to try some of the island's famous product - Black Pudding!  trouble is there are so many to try .......

Sunday, 13 December 2015

Gorgan Wall Marine Geophysical Survey 2015

Hunting the drowned “Red Snake” – The Sasanian Persian Empire’s Great Walls



 One more field site for the year - at least I think so!  A couple of years ago Prof. Eberhard Sauer (Edinburgh University) got in touch as he has had a 10yr project investigating the “Red Snake” of Persia.  This is better known as the Gorgan Wall that once ran near the border of Iran and Turkmenistan from the Caspian Sea in the west and the Elburz Mountains in the east.
At a known length of over 195km it was pretty significant as an ancient line of defense.  However, not so today as the westernmost part not visible even to archaeologist in the present landscape. The problem with the wall is that it was constructed of mud bricks and so the ravages of time and the deconstruction (robbing) of bricks for use means that it is often difficult to see today.  However there is a silver lining, or at least a geophysical signature silver lining, that results from the use of bricks.  That is that the firing process of making bricks can give a strong magnetic signature to the bricks.   To make them requires a few key ingredients, namely a good clay with some larger silt or sand grains and water.  Lucking the clay is in abundance all along the wall’s path but water in this semi-arid area can be a problem.  So a solution was found by diverting local rivers to run feeder canals to a ditch that ran along the length of the wall thus providing not only the vital water but at the same time a quarry for the clay and when the wall was completed an extra defense line!
C5-6th   Kiln 
195km of wall requires quite a few bricks – it has been estimated that over 200 million in total were used!  Making these bricks was achieved using temporary field kilns set up all along the path of the wall at approximately 50m intervals.  The wall was garrisoned by an arm of over 20,000 soldiers barracked in at least 30 forts. The project team have spent the last few years excavating some of these kilns together with some of the forts and sections of the wall itself.  They have also investigated a sister wall, the Tammisheh Wall that ran from the southeast corner of the Caspian south to the Elburz Mountains.  Through C14 and OSL (Optically Simulated Luminesance) dating their work puts a construction date on both walls to the Sasanian Persian Empire between the 5th and 6th Century AD.

So what am I doing here?  The western extent of both walls is unknown.  Historical writing describes how the walls enter the Caspian Sea and certainly the Tammisheh Wall can be traced almost to the modern shoreline but where it goes after that is unknown.  Some descriptions even suggest that both walls were joined up. So we are back again to our old problem of changing sea levels and with it the usual battering that this can give to the landscape and our human endeavours. 

So I am here to help out with the searching for the walls, both on the sea floor and beneath it if they have been covered by more recent sediments.  We were looking for upstanding bricks or a scattering of bricks on the seafloor with the hope they would not have disintegrated.  Beneath the seafloor the hope was again to find lines of bricks or mounds.  Perhaps we would also see the cross –section of the trench that ran along the wall.  With the magnetic signature associated with the kilns on land this might stand out too but for this first preliminary survey I chose to use the Tritech Seaking Parametric Sub-bottom Sonar that we have found so effective in the shallow waters of Orkney together with an ultrahigh resolution Tritech Starfish 990kHz Sidescan Sonar. A great advantage of both these systems is that they can be taken as hand luggage on flights!
small boat work with Tritech Sub-bottom sonar and Starfish Sidescan
We started with the Tammisheh Wall as the projection into the Caspian is better known. The parametric sonar proved worthwhile once again despite the occasional gas blanking by picking out a strong reflection from the brick scatter on the sea floor.  The signature of this continued as it became buried further offshore with up to 2m of sediment.  After approximately 3km it abruptly disappeared or terminated.  The scatter on the sea floor was also mapped with the sidescan sonars from which the surface brick scatter was readily identified together with a number of linear features.

Given the time available for this trip and the relatively less knowledge on where the Gorgan Wall might be crossing the shore line we had a much larger potential target area to cover.  With a few days of poor weather (yes the Caspian does get rough with over a 1m wave and swell heights) we covered a large area but without finding any definitive wall signatures.  So more and better targeted data acquisition is needed for the marine side here.  What I now propose is to return and try with a magnetometer and an electromagnetic ground conductivity meter to survey from the last known western point of the wall across the land and shallow lagoons to the shore.  If we can trace this then we stand a much better chance of mapping it offshore, if that is where it goes. Video summary of the trip:



I had a fantastic crew out with me on the water (I cannot thank Hamid, Bardia and Hassan enough) and also back in the base as the joint project leaders, Dr Jebrael Nokandeh of the National Museum of Iran and Eberhard have assembled a talented team of archaeologists for the project.
So, another privileged trip to work with some great people, such friendly banter, engaging conversation, fantastic archaeological potential, some great food and wonderful scenery – the bird life on the Caspian is stunning!  I can’t wait to return next summer equipped with magnetometers and electromagnetic gear to continue the hunt.

Iran-British Gorgan Wall Project Team
Dr Jebrael Nokandeh (National Museum of Iran); Mr Hamid Omrani Rekavandi (Iranian Cultural Heritage, Handcraft and Tourism Organisation of Golestan Province); Bardia Shabani, Hassan Taji, Mohammad Ershadi, Maryam Hosseinzadeh, Mohadeseh Mansouri, Meghdad Mirmousavi, Mohammad Bagher Bayati Mehdi Jahed, Alireza Salari, Esmaeil Safari Tamak, Majid Mahmudi, 

Friday, 6 November 2015

Seismic Reflection - Chew Bahir

Return to Chew Bahir – the Seismic Reflection Story


Two years ago we (St Andrews, Dei Huws at Bangor and Tigistu Haile at Addis Ababa University) visited the Chew Bahir basin in order to acquire geophysical data in advance of the HSPDP (Hominin Sites and Paleolakes Drilling Project) drilling a hole to investigate the palaeo-climate of the last 500 thousand years.  The overall aim of this programme is to investigate palaeo-climate at key African Hominin sites. During the first geophysical survey we used electrical resistivity tomography near to where previous shallow (20m) boreholes had been drilled by the HSPDP group on the lake bed at Chew Bahir.  In addition to our shallow geophysical surveys Tullow Oil had also completed a programme of deeper hydrocarbon seismic reflection investigation.  The results of both these were used together with the shallow drilling to pick the location of the deeper borehole.  In 2014 this hole was drilled with much success and is now undergoing extensive investigation at a number of research institutes.

So what were we doing back in the basin? An important part of trying to understand the core sequence and determine the environmental change that it represents requires that we have confidence in how the core fits with the larger geological story.  This means a better knowledge of how to extrapolate the data away from the core.  This requires geophysical data and the best type for this is high resolution seismic reflection.  So this was what we went to do.


Our data was acquired with a 96 channel Geometrics GeodeSystem with a 40kg Propelled Energy Generator impact seismic source.  After a walkaway survey we decided to shoot the data with a 32m source offset and 4m geophone interval.  We shot the data with 72 fold coverage along two crossing reflection lines over the borehole site and an additional 3 refraction lines to evaluate near surface velocities.  The seismic crew consisted of the previous team joined by Dr Erica Galetti from Edinburgh University and Yemane Kelmework from Addis Ababa.  Tim Raub (St Andrews) also came along to add his geological savvy to the project and to look at a number of other geologically-relevant sites (see later blog on this for some stunning new sites!). The initial data looks very encouraging with numerous reflectors identified.  Processing will tell how good the final data will be and that will happen over the next few weeks.

Despite the relatively dry year with almost drought conditions we managed to grab the data just in advance of the little rains starting.  Downpours on the last morning flooding the local roads and turning the dried lake bed into a gloopy mass that was impossible to drive on. 

During the field work we camped at the village of Arbore and employed a fantastic cook from a nearby town.  The field work would not have gone so smoothly without her keeping us fantastically fed on traditional Ethiopian foods (injera, shiro, and of course some local goat) and also without the help of our two drivers, Yared and Solomon. 

Wednesday, 15 July 2015

Ice Age Island 2015

Ice Age Island – the Saga Continues

So we have returned for another season in Jersey as part of a three year project to explore the deep prehistoric past, from exploration of the island caves, through the archaeological excavation of hunter gather camps preserved in the island’s interior, to the iconic sites at La Cotte de St Brelade.  In all of these locations we aim to discover why this remarkable landmass attracted Neanderthal and modern humans at different time periods.  Over the past 3 years we have been acquiring geophysical data both onshore and offshore in order to re-create the landscapes of the past.  We have also had a number of investigation sites such as the one at Les Varines shown below.

Les Varines dig 2015

Earlier in the spring we acquired 2D electrical resistivity tomography (ERT) data at the site, which together with boreholes drilled through the sequences allowed for the targeted expansion in the excavation.

At the other side of the island we are trying to survey cliff sections that will give us further insight to the history of climate change in Jersey over the last 200,000 years as recorded in the sediment sequences, and hence palaeogeography of the La Cotte site.  In Portelet Bay to the south east of St Brelades there is a particularly well exposed Pleistocene deposits.  The only problem is that its 15m high and loose – a job for extreme geophysics!  By abseiling off the top of the cliff we were able to clean a sufficient amount to achieve mapping, photography, sampling (for OSL dating, palaeo-climate and palaeogeographic setting) and a geophysical profile.  The geophysics consisted of both magnetic susceptibility and DC resistivity.  The mag did not produce much differentiation however the DC resistivity mapped distinct boundary changes within the various units. The preliminary results are shown below and you can visit here for some live action!



Some preliminary results

See some of the previous work for the site at an older blog:


The project is sponsored by Capco Trust and supported by the Tourism Development Fund.
For more information also see:



Wednesday, 10 December 2014

Sanday, Orkney Core Sampling

The Storm Chasers are Back!

Actually the Rising Tides team are back up in Orkney, Sanday to be precise, trying to chase environmental signatures of the past while also trying to dodge a weather bomb!  So what is it we are actually doing and what is a weather bomb?  As those of you who have read any of our previous work will know we are particularly interested in understanding palaeo-environments, landscapes and geography in relation to past societies.  Our work on the mainland, that is the mainland of the Orkney Isles, has reconstructed drowned landscapes through geophysical, coring and diving work.  On Sanday, we have come chasing the records of a drowned forest.  Sounds familiar? Well yes, in some ways it is similar to those sites on the west coast of Wales, and from a much older time frame  the sites at Happisburgh where we found the oldest footprints outside Africa last year.  Here in Sanday however we are trying to link back to that critical period in the development of human behaviour, the change from hunter-gatherer in the Mesolithic to the farmers of the Neolithic.


So why Sanday? Well, for one reason that a “drowned” forest has been written about in the past. In 1867, in the History or Orkney the Rev George Barry reported a “strong tradition that the harbour of Otterswick in Sanday was once a forest, which was destroyed by inundation. “and further, a sample of the trees was obtained by Traill-Dennison in March 1890.  We walked the beaches here and ran some speculative geophysics last summer with encouraging results that led us to a bay on the west coast of Sanday where with great luck on a particularly low tide we spotted a small raft of peat.  Coring and measurement of its elevation confirmed that it was equivalent to the Otterswick Bay samples and so here we are, back again on a series of very low spring tides to get further samples. 


So what’s the problem? It’s December, there is limited daylight here and we have the “storm of the century” approaching (think The Perfect Storm)!  The task therefore is to get some samples and undertake some more geophysics before it hits.  The tactics – geophysics (always geophysics) but most importantly some serious extreme geoscience sampling – a JCB! (for those of you who are not familiar with this great vehicle, and actually its not a JCB that we are using, then it’s a backhoe).
The results – instant sections, great samples and all done before today with its horizontal sleet and snow.  We have now dug four test pits (typically in fading light at low tide, actually it was dark!) and found the peat.  Significantly the peat we have dug appears to be full of freshwater molluscs at the base but towards the top there are articulated marine bivalves as well as whelks and other marine molluscs.  This is what we are after – it documents the onset of marine conditions and allows us to begin to understand how marine waters flooded across these Mesolithic landscapes.  Elsewhere we have been augering in probable infilled bays where we discovered more than 2.5m of peats and sands alternating throughout the core.  This documents the interaction between the land and the sea and excitingly these cores are very close to a multi-period archaeological site that started in the Neolithic and continued intermittently until the Viking period.  So mission accomplished so far….watch this space