The series of earthcaches Explore Arenberg proposes to you a geologic stroll to discover the architectural and natural heritage of Arenberg.
Introduction:
Our subsoil contain a lot of natural and human-related underground cavities (estimated at over 500 000 in France). Once abandoned or forgotten, these cavities represent a potential risk of collapse.
Two types of cavities:
Natural cavities appear in geological formations susceptible to the action of water. The water containing carbon dioxide infiltrates natural fissures of the subsoil and dissolves chalk and limestone. It forms tunnels and cavities.
Artificial cavities are created by human activities: mines, quarries, wells, tunnels, caves ...
Ground movements:
There are mainly two types of surface ground movements: subsidence (no cavity opening) and collapses (opening of a cavity surface)
Subsidence is a flexible, seamless and gradual deformation of the ground surface resulting in a shaped depression bowl, generally with a flat bottom and bent edges.
A collapse is a violent lowering of the surface (from several hectares to several meters of depth) produced by the rupture of the roof of an underground cavity
A sinkhole is a localized but violent collapse which takes the form of a funnel or a crater. The diameter and depth of the cone can vary from a few meters to several meters.
"Mare à Goriaux":
The company of Anzin mines put into service in 1903 its mining extraction site of Arenberg.
In 1916, at 2 kilometers from the mining extraction site, 3 ponds appeared!
In 1930, the 3 ponds join and form the "Mare à Goriaux" which todaystreches on 95 hectares.
Reminder on "Earthcaches": There is no container or logbook on the given coordinates. Just visit the site and answer the questions by e-mail or by the Message Center.There is no need to wait for my reply, feel free to log immediately after. If the answers are incorrect, I will let you know. Happy caching!
To validate your visit:
1-What is the origin and the meaning of the word "Goriaux"? (only the correct answer of the information board wil be accepted)
2- What are the names of the 3 ponds of the "Mare à Goriaux" and of the ditch next to these ponds?
3- With the explication of the formation and with your observations, what is the ground movement at the origin of the "Mare à Goriaux"? Justify briefly
Answers to questions 4 and 5 are not available (information board damaging)
4- What is the maximal depth of the "Mare à Goriaux"? answer was: 4m
5-. The reed beds decline, but what are the 2 forms of regression? answer was: Régression par atterrissement et par approfondissement.
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