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Dune Land

A cache by Gamboy Send Message to Owner Message this owner
Hidden : 11/15/2015
Difficulty:
1.5 out of 5
Terrain:
1.5 out of 5

Size: Size: other (other)

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Geocache Description:

Dune Land

Les Dunes

Les dunes littorales ou dunes bordières se forment sur le long des côtes basses où les vents et l'apport de sédiments par la dérive littorale permettent l'accumulation de sable sur les plages. À marée basse, le haut de plage est asséché par le vent ce qui permet le transfert des sables vers l'intérieur des terres, essentiellement par roulage et saltation. La largeur de l'estran est donc un facteur primordial du bon développement des dunes: plus il est large, plus la surface de déflation éolienne et donc la quantité de sédiments soufflés sont importantes. Dans le processus de formation des dunes, les plantes pionnières jouent un rôle fondamental, assurant le dépôt, la fixation et la stabilisation de l'accumulation dunaire. Ces plantes sont adaptées à l'instabilité du substrat et présentent de longues racines traçantes. La dune littorale est donc une forme d'accumulation sédimentaire fixée par une végétation psammophile, il s'agit d'une construction biogéomorphologique. Les dunes littorales, poussées par les vents, peuvent envahir graduellement les terres si la topographie de l'arrière-côte le permet; ce fut l'une des raisons de leur fixation le long de la côte landaise par la plantation d'une forêt de pin maritime. Lors des tempêtes, les dunes constituent une réserve de sable face à l'érosion des vagues: l'attaque directe des vagues entaille la dune et le sable prélevé est transféré dans les petits fonds. Il remonte normalement lors des périodes de calme sous l'action des houles.

Extrait de Wikipédia

The Dune Bell


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The Dunes

Dunes form where constructive waves encourage the accumulation of sand, and where prevailing onshore winds blow this sand inland. There need to be obstacles—for example, vegetation, pebbles and so on—to trap the moving sand grains. As the sand grains get trapped they start to accumulate, starting dune formation. The wind then starts to affect the mound of sand by eroding sand particles from the windward side and depositing them on the leeward side. Gradually this action causes the dune to "migrate" inland, as it does so it accumulates more and more sand. Dunes provide privacy and shelter from the wind.

Ecological succession on coastal dunes

As a dune forms, plant succession occurs. The conditions on an embryo dune are harsh, with salt spray from the sea carried on strong winds. The dune is well drained and often dry, and composed of calcium carbonate from seashells. Rotting seaweed, brought in by storm waves adds nutrients to allow pioneer species to colonize the dune. These pioneer species are marram grass, sea wort grass and other sea grasses in the United Kingdom. These plants are well adapted to the harsh conditions of the foredune typically having deep roots which reach the water table, root nodules that produce nitrogen compounds, and protected stoma, reducing transpiration. Also, the deep roots bind the sand together, and the dune grows into a foredune as more sand is blown over the grasses. The grasses add nitrogen to the soil, meaning other, less hardy plants can then colonize the dunes. Typically these are heather, heaths and gorses. These too are adapted to the low soil water content and have small, prickly leaves which reduce transpiration. Heather adds humus to the soil and is usually replaced by coniferous trees, which can tolerate low soil pH, caused by the accumulation and decomposition of organic matter with nitrate leaching.[9] Coniferous forests and heathland are common climax communities for sand dune systems.

Young dunes are called yellow dunes and dunes which have high humus content are called grey dunes. Leaching occurs on the dunes, washing humus into the slacks, and the slacks may be much more developed than the exposed tops of the dunes. It is usually in the slacks that more rare species are developed and there is a tendency for the dune slacks soil to be waterlogged and where only marsh plants can survive. These plants would include: creeping willow, cotton grass, yellow ins, reeds, and rushes. As for the species, there is a tendency for natterjack toads to breed here.

Excerpt from Wikipedia

DuneScape

Loguez cette cache "Found it" et envoyez-nous vos propositions de réponses soit via notre profil (Gamboy), soit via la messagerie geocaching.com (Message Center), et nous vous contacterons en cas de problème. Les photos avec la dune en arrière-plan sont les bienvenues (mais pas obligatoires).

  1. Quelles sont les zones définies pour la topographie de la dune de Labenne ?
  2. Comment se déplace le trait de côte à Labenne depuis les années 1960 ?
  3. À quoi correspondent les fascines ?
  4. De qui sont les photos du panneau d'information sur les dunes placé au point repère de la cache ?

Log this Earth Cache as "found it" and send us the answers to the following questions via our geocaching profile or the geocaching messaging system, we will contact you if a problem arises. Photos are not required but they are always welcome.

  1. What are the zones used to describe the topography  of the Labenne dune?
  2. How does the Labenne coastline move since the 60s?
  3. What are the fascines?
  4. Who is credited for the photos on the information panel found at the reference point of the cache?

Additional Hints (Decrypt)

[FR] Vy l n ha cnaarnh q'vasbezngvba nh cbvag qr eéséerapr. A'bhoyvrm cnf qr ertneqre yrf onïarf...
[EN] Gurer vf na vasbezngvba cnary ng gur ersrerapr cbvag. Juvyr lbh ner urer, gnxr n ybbx ng gur onïarf...

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)



 

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Coordinates are in the WGS84 datum

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