Archaeological
prospecting
with a
gradiometer
Magnetometry
Mapping
Magnetic noise
Equipment
Field procedure
Examples
Get in touch
Norwegian

 
Gradiometer in use at a house cluster near Brønnøysund, Nordland, northern Norway
In this context, archaeological prospecting can be defined as searching for and mapping concealed and partially concealed prehistoric remains using various scientific methods and equipment. Geophysical instruments are particularly important here, gradiometers, georadar and electrical resistivity meters being especially widely used.

Such non-destructive methods have gained relatively little foothold among Scandinavian archaeologists, who mostly favour mechanical topsoil stripping, probing and trial trenching when they need to determine whether a piece of land conceals prehistoric remains. This contrasts greatly with the situation in many other countries, notably the British Isles, where most of the methodology and instrumentation were developed.

One reason for the limited interest for these methods among many Scandinavian archaeologists may be the view that the bedrock and soil here are mostly unfavourable for such methods. Indeed, as regards magnetometry it is not unreasonable to think that the bedrock and soil in large parts of Scandinavia are so rich in magnetic minerals as to be an obstacle to the application of magnetic methods to seek prehistoric remains. This magnetic ‘noise’ would simply drown any signals from prehistory. However, concentrations of relatively magnetic stones have actually proved to have a positive effect, revealing prehistoric remains.

 

Magnetometry

This kind of geophysical archaeological prospecting has several advantages compared with methods commonly applied in Scandinavia when the archaeological potential of an area is to be assessed. These advantages include:
 

  • quick, reasonable investigation of large and small areas
  • no need for several co-workers
  • expensive and destructive mechanical topsoil stripping is avoided
  • it is non-destructive − neither the surface, the topsoil nor archaeological remains are damaged
  • trial pits and trenches need not be dug at random
  • computer-processed maps are prepared showing where possible features of interest seem to be located, and their general appearance
  • archaeologists receive information enabling them to assess a site as an entity so that they may concentrate on selected parts that are of greatest interest to them, and to place excavation results in the context of the entire site
  • good relationships to landowners are created and maintained

Under favourable conditions, with good magnetic contrast (positive or negative anomalies) between archaeological features and their immediate surroundings, it is possible to recognise structures (remains of buildings, hearths, pits, graves, etc.). Sometimes, a firm interpretation can be made, or simple probing will confirm a suspected feature. In doubtful cases, it may be necessary to dig a trial pit or trench, but you will have specific evidence indicating where it is most advantageous to dig.

Such archaeological prospecting is especially favourable
 

  • for pilot projects linked with development plans
  • for pilot projects linked with research projects
  • as an integral part of a research project
  • prior to planned excavations
  • as a step in management plans and in presenting sites to the public

Mapping with a fluxgate gradiometer

Backed up by long experience from geological and archaeological field mapping in Norway, RB GeoArk has for many years been carrying out magnetometric investigations of prehistoric and potential prehistoric sites on behalf of archaeologists and others. Some 70 areas at more than 40 sites from Tromsø and Laksefjord in the north to Stavanger in the southwest of Norway, and also on the Faeroes, have so far been investigated.

The equipment used for this mapping is a gradiometer, an advanced form of magnetometer specially developed for rapid archaeological prospecting. This geophysical instrument registers small variations in the magnetic signals emanating from the ground. These signals are processed by a computer program and printed out as maps.
 
What can a gradiometer reveal?

In principle, a gradiometer can reveal anything that produces a magnetic contrast (an anomaly) relative to its immediate surroundings. Due to variable bedrock, superficial deposits and soils, this will vary somewhat from place to place and country to country.

Although a fairly rough survey may reveal large postholes, closely spaced measurements are generally necessary to recognise patterns that can reasonably definitely identify buildings constructed with posts. Sometimes buildings can be recognised by linear anomalies produced by beam slots or external drainage ditches, and regularly arranged midline hearths, phosphate-rich and/or trampled earth floors, stone floors and corner stones (pad stones) may also offer good magnetic contrast. Buildings constructed solely of timber or turf are difficult to identify directly.

Objects and features that are most likely to be revealed are
  • iron artefacts
  • accumulations of stones (e.g. burial cairns, building foundations, cooking mounds)
  • burial mounds, if they are constructed of material that differs from its surroundings, or contain features or material that provide a local magnetic contrast, such as a stone cist, a stone setting, a ring ditch, iron or ceramic artefacts, or a cremation patch
  • hearths, patches of burnt ground, cooking and charcoal-production pits (because some clay minerals in the soil become magnetised when heated above ca. 600 °C)
  • ceramics and pottery kilns
  • remains from iron or copper production
  • phosphate-rich soil
  • ditches
  • beam slots and postholes
  • stone rings, circles and settings
  • paths and other occurrences of trampled ground or compact stone cobbles

Examples of areas that have been mapped in Norway
Prehistoric remains at Tilrem, near Brønnøysund, Nordland An Early Iron Age longhouse near Klæbu, Sør-Trøndelag Remains of an Iron Age house cluster north of Brønnøysund, Nordland, north Norway A prehistoric site at Hadsel, Vesterålen, north Norway
Concealed prehistoric remains at Hokksund, Buskerud An enigmatic site at Inderøy in Nord-Trøndelag Assumed longhouses at Garnås, near Nesbyen in Hallingdal A possible Iron Age longhouse on Kvaløy, near Tromsø, northern Norway

RB GeoArk

In addition to gradiometer surveys, RB GeoArk also undertakes other geo-archaeological and geological investigations, including studies at rock-art sites, bedrock mapping and petrographic studies, as well as mapping of cultural heritage sites, archaeological information services (signs, brochures, booklets, etc.), drawings and watercolours with archaeological, historical or landscape associations, and test excavations (subject to prior permission).

Prehistoric site mapping

RB GeoArk personnel have long, and countrywide, experience of seeking, recording and describing prehistoric sites for the regional museums in Norway, partly in connection with the production of land-use maps for the Norwegian Mapping Authority. Link: https://askeladden.ra.no

Presenting archaeology for a wider public

RB GeoArk personnel have carried out many assignments in connection with the presentation of cultural heritage sites and archaeological discoveries, chiefly in central Norway. These have included editing a bi-annual magazine, writing chapters in books on local history, preparing texts and illustrations for information signs, booklets and pamphlets, and acting as guides on excursions.

SPOR, a magazine published at the Department of Archaeology and Cultural History, Museum of Archaeology and Natural History, Trondheim http://www.ntnu.no/vitenskapsmuseet/les-spor-her

Local history:
Helgeland historie, vol. 1 (1985)
Leirfjord bygdebok, vol. 1 (1985)
Fosen historie, Chap. 2 (2005)

Fotefar mot nord, no. 17: Facing the Forces (24 pages describing sites near Brønnøysund, Nordland) http://fotefar.no/Filnedlasting.aspx?MId1=3354&FilId=1510

Guide to 10 selected cultural heritage sites in Steinkjer, central Norway (32 pp.) http://content.yudu.com/Library/A1nnve/Veivisertil10utvalgt/resources/13.htm

Various information signs and exhibitions in central and northern Norway

Illustrations of archaeological and historical sites and events

In connection with the above, many watercolours and drawings have been made to illustrate situations from prehistory and historical time for publications, TV programmes and signs.

Examples


Stone Age settlement near Kristiansund

Burial ground at Helge, Steinkjer - illustration for a sign


A reconstruction of a pagan hov outside Trondheim, based on excavation results
- Illustration in Spor


Kjøpmannsgata, a street in Trondheim about 1250 AD - book illustration

Archaeological excavations

RB GeoArk has personnel with many years’ experience throughout Norway of participating in and managing archaeological excavations, mainly on behalf of the regional museums. When prior permission has been obtained, we can undertake such excavations on our own behalf or for clients. Such an excavation is ongoing at Klæbu, central Norway, in connection with the longhouse presented elsewhere on this web site.

Gradiometer in use at Tilrem near Brønnøysund, Nordland, northern Norway
Please get in touch if you have a problem that can perhaps be solved by gradiometer mapping or you need other services which we offer. We can discuss it, and you can get an estimate.
 

Please send a mail to rbinns@online.no or ksbinns@online.no
, ring (+47) 73524703, 91644950 or 95902251, or write to

RB GeoArk, Strindveien 64, NO-7052 Trondheim, Norway

 
 
 
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Magnetometry
Mapping
Magnetic noise
Equipment
Field procedure
Examples
Get in touch
Norwegian