[EC] Pingo's in Broekhuizen EarthCache

Broekhuizen is a hamlet near the scenic and fairy-like city of Koekange. And not only is it an excelent shortcut for the inhabitants of Koekange to reach the city Meppel and the highway A28! It has a lot more to offer!
In Broekhuizen you can find a lace of Pingoruins! Four Pingo’s in one line, very nice to see, and because of that we have made this short walk for you! All four lakes are formed by winning peat from the original bog they were about 150 years ago. This bog was formed in so called pingo-ruines during many thousands of years.
This cache will teach you a little bit about a pingoruin, so read the text below and go see all four pingoruins. The total distance is approximately 4 kilometers.

Pingo

In the second last ice-age, named the Saalien, Drenthe was covered with an thick layer of ice. That ice came from Scandinavië. The forests disappeared, and the wind blow over the empty landscape. At that time Drenthe looked much like an artic landscape. The wind and land-ice transported sand, clay and grit into the whole area. Mixed together this three materials formed boulder clay that you can find almost everywhere in Drenthe’s ground. The glacial ice also transported big boulders to Drenthe, which where later used by farmers to build there graves, better known as dolmens.
During the last ice-age, the Weichselien, the pingo’s where formed. Pingo is Inuit for hill, A pingo is a small round hill with inside of it a frozen lens shaped ice core, that can arise in areas where the subsurface is permanently frozen (permafrost). Groundwater underneath this frozen subsurface is standing under enormous pressure and when a crack appears in the frozen subsurface, the water is being pushed up. The water is unable to go trough the frozen upper ground, thus freezes and expands. Underneath this ice, the water remains under high pressure and keeps pushing the ice and upper ground up; a pingo is born.

Pingoruin

In the Netherlands there was a tundra climate during the Weichsel-glacial, a period within the Pleistocene epoch about 116.000-11.500 years ago. In area’s where the groundwater was close to the subsurface pingo’s could arise. At the end of the Weichsel-glacial though, the temperature was slowly rising. At first the top of the pingo would melt and some time later also the ice core inside. The pingo collapses and sediment rolls from the sides of the hill down to the ground. What remains is a depression in the landscape surrounded by a small rampart of sediment; known as a pingoruin. In the depression arises a lake that over a period of thousands of years is being filled up with bog. The bog contains valuable information about the vegetation, which can be used to reconstruct the climate during the upholstering of the pingoruin.
Pingoruins are the best documented geological climate archives in the Netherlands and precious study objects for quaternary geologist.


Geocaching/Earthcaching

Park your car at: N52 41.397 E6 18.121

Park along the road so you don’t bother any persons living over here.

In order to complete this Earthcache you have to visit all four Pingo ruins, do that by cycling or walking, don’t go by car!

To prove that you've visited al four Pingo's you have to answer the following qeustions:

Task for Pingo 1:
Standing at the coordinates, how many stables can you see when looking east?

Task for pingo 2:
How many Pollard Willows do you count next to the Pingo ruin, at the right side of the house?

Task for pingo 3:
Take a photograph of one of your teammembers or yourselve while holding your GPS. With the pingo in the background, upload that photo with your log.

Task for Pingo 4:
At this point you have an excellent view at the Pingo, during the summer it may be invisible because of the corn. When looking east from this point you san see a big tree. What kind of tree is this?

Now that you've visted al four Pingo Ruins there is only one question left.

Task 5:
What, if any, evidence can you see here that suggests these are pingo's and not just lakes?