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An Archealogical/Geographical question, anyone?

• Message 1.Β 

  Posted by Nagrad (U2474564) on Saturday, 12th November 2005

  I am a geography student and i have a question which i was wondering whether any of you could help me with. From my studies and own research I have gathered some information on the topic of soils, which is ultimately what my question is on. I understand that most soils contain four basic components; air, water, minerals and organic matter. Soils are formed, from the breakdown of rock due to weathering, therefore the content of the soil, colour, texture etc. are all dependent on the parent material (and of course the type of vegetation that grows from them). However to build up 1cm of soil can take over 1000 years. Even in some of the most harsh climates it takes many years for the rock to be weathered. So if it takes over 1000 years for the build up of such a small amount of soil how come the ruins of buildings, can get covered by soil in half that time, sometimes even less. Under specific circumstances such, as volcanic eruptions and glacial movements I understand how it could happen, but why in a temperate climate such as Britain? How is enough soil created from the weathering of rock to build up over these buildings. In urban areas obviously, new buildings are placed ontop of the old, so there are no foundations to find. However most of the buildings excavated are small farm dwellings that tend to be far away from largely populated areas. This could mean that vegetation has an effect on the build up of soils, yet vegetation tends to take out of the soil a little less than what it puts back in when it dies. So ultimately my question is why do these ancient buildings need to be excavated? How does the soil build up so quickly and cover the foundations of the buildings not more than a few hundred years old and usually when you see them excavated, they appear fairly deep in the earth?
  
  Sorry its so long, but its a question thats been bugging me for a while. Anyone that wants to add, correct me or anything feel free, thanks in advnace.

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  Posted by Nik (U1777139) on Saturday, 12th November 2005

  This is a very interesting issue of primarily geology that has consequencies for achaiology.
  
  You said correctly that soil is formed by the decomposition of inorganic and organic material with the aid of air and water etc. Now, you mentioned a theoretic 1cm in 1000 years but then I suppose that is in case there is no wind or water to transfer dust and particles on it... because if we take into account winds and waters then certainly it is not 0,00001m/yr but well more than that.
  
  To give you a nice example, one that I know from my home region Macedonia, go to a map of Greece that has the major cities and look out for a small city in the north west of Thessaloniki that is called 'Pella'. That is actually situated next ancient Pella, the capitol of Macedonia. You see well that Pella is situated kilometers away from the sea ... however ancient Pella was actually a harbour!!! Nearby cities like Veroia were coastal cities till medieval times (in Veroia still today the lowlands are called by locals 'the bay' and indeed from up the mountain it looks like a bay). All that big change happened in 2000 years due to the nearby river Axios (on the east of these cities). Axios was never a big river (southern balkans are not famous for rivers) so if such a small river can do that change then imagine what larger rivers like in America or Africa can actually do. You may find 1000s of such examples all over the world.
  
  Yes England also has not the biggest rivers in the world (although Thames is many times larger than Axios that used to be the biggest river in Greece) but indeed it has many rivers here and there that continuously carry material which is dispersed with the aid of the wind.
  
  Now since human cities and villages were always near rivers and the sea were changes are more intense then it is more than normal that the remains of houses (usually the underground supports and level ground) of more than 1000 years old are found some meters under the surface. Only in those places that life went on and there was an human effort to maintain the old monuments did the monuments remain on surface.
  
  Of course monuments of very large size (like castles) and those that were built in higher altitudes (thus possibly the opposite effect was going on - material was being subtracted by them by wind and water and driven on the lowlands) did not have the same fate - mind you depending on the environment really impressive monuments could be lost like the Sphinx that was almost all covered by sand from late 3millenia till early 2nd BC when pharao (again I forgot him!) did the first known archaiological excavation to bring it back to surface!!!

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  Posted by Rurfus (U1800117) on Saturday, 12th November 2005

  
  Good question. Only to give a brief outline there could be several reasons to account for such things. One is sometimes the remains of old buildings are incorporated into later structures. This was very common in cities such a Rome. Many of the Medieval church foundations were Roman, nobody had cared to clear them and put new ones in.
  
  In the case of fire, which would occasionally destroy a significant part of a settlement, they wouldn't systematically clear every last bit of waste. They would often build right on top of the remains. A more famous example of this can be the archaic city of Troy.
  
  Another thing that can often be misleading is, sites are reconstructed when they are found. That is to say, when large intact fragments of something such as a column are found they are rebuilt.
  
  Being specific to London and other urban centre's in Britain. Following the withdrawal of the Romans from Britain the urban centres were abandoned, London had already been in decline for some time before.
  
  This is of course only a brief brainstorm but I hope it gives you some idea.
  

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  Posted by maraudingsaxon (U3567176) on Tuesday, 25th April 2006

  This an interesting thread.
  In Britain, like troy, you can find buildings built on top of earlier buildings. In Colchester the Norman castle is built on top of the roman temple. Many medieval churches are built on or developed from saxon churches. Which in turn may have in turn been built on roman religious buildings, which may have been built on possibly earlier iron age/bronze age shrines. In fact there is a rule of archaeology that states: Continuation of land use. Why build somewhere new when you can use an exisiting site.
  As to soil. If you build in a valley basin and for whatever reason the building gets knocked down. Soil erosion on the valley sides with move soil down onto the valley floor, quickly covering any remains of your building. Also another reason in Britain is farming. Ploughing is constantly turning over the soil and burying any remains.Hope this helps.
  
  
  
  
  
  

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  Posted by an ex-nordmann - it has ceased to exist (U3472955) on Tuesday, 25th April 2006

  Here is an answer from an archaeologist to the same question posted on another website last year. I can't improve on it so forgive me if I cut and paste its contents here:
  
  
  
  
  
  "Well, that depends on the site. Some comes from erosional activity, in other words if the site is in a low area, then the soils from the surrounding hills has a tendency of moving down slope. Not so much as a land slide but by small amounts with rain and snow melt.
  
  The next important area of erosional activity is blowing soils. This is common in dry areas such as the middle east, Italy and Africa. But even in temperat climates, blowing soils can be many inches thick. In the case of blowing soils, the site can be on the top of a hill.
  
  The next is atmospheric soils. This can range from the microscopic dust from space to huge amounts of volcanic dust and ash. Pompaii and Herculanium were buried buy volcanic debris. It is estimated that 1/2 inch (12 mm) of dust falls on the Earth every year! Grass, weeds, trees, and other vegitation capture this material and it acts as a nutrient base.
  
  If the site is near a river or the ocean, then the action of flooding and wave action can have a significant impact on how much or little covers a site. In the case of flooding, this can reach many hundreds of feet in depth over time. If you look at the Mississippi valley in the US, the flooding has buried a canyon not unlike the Grand Canyon over the last 12,000 years.
  
  If a site is covered by water for a time, this can also create layers of sediment to cover a site. This has happened in earthquake and volcanic regions too.
  
  There are other reasons for sites to be buried but these are the most common.
  
  Some others that are also important are man made reasons such as:
  
  Towns are rebuilt on the ruins of old towns that were burnt down or destroyed in an earthquake or by volcanic activity or war.
  
  Soil is intentionally brought in to build a hill so that the town is easier to defend and this soil covers the existing town.
  
  In some parts of the world, mud brick is used to build buildings and over time this erodes back into mud, espcially in areas with infrequent rains.
  
  So there you have some of the ways sites get buried, even in the UK."
  

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  Posted by DocMike15 (U3167117) on Tuesday, 25th April 2006

  I'm no deposition expert (to say the least), but its surprising just how quickly things do get covered. There is a church in London (between Holbern & Tottenham Ct Rd) which is at least 8 feet below the current pavement level. Rubbish, vegetation (the post-Roman periods of many towns are called 'Dark Earth' layers because of the rich loamy soil that occurs in thi layer), blown soil, etc all can build up soil. Deliberate demoltion or removal (stone-robbing) is alo a factor.

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