Monte da Lua
The Earth's surface is the result of a balance between the planet's internal forces, that create volcanoes, mountain ranges and depressions and move the rigid chunks of the crust around (the tectonic plates) and the never ending effects of the external atmospheric elements and the rivers and oceans (basically air and water, liquid or solid) . Internal forces create topographic features, irregularities, and air and water (with the help of the long geological time) smooth them out. Where there is a hill, there's material moving to fill a valley.
A gully is a landform created by running water that sharply erodes the soil, typically on a hillside. Gullies resemble large ditches or small valleys; their size varies from meters to tens of meters in depth and width. When the gully is being formed, it acts as a preferential channel and the water flow rate can be substantial, reinforcing the erosional potential and increasing the soil cutting action.
Gullying, or gully erosion, is the process by which gullies are formed. Hillsides are more prone to gullying when they are cleared of vegetation, through deforestation, over-grazing or otherwise. The eroded soil is easily carried array by the flowing water, normally during short, intense storms. The total soil loss from gully formation and the consequent downstream river sedimentation can be sizable. Gullies reduce the productivity of farmland where they incise into the land and produce sediment that may clog downstream water bodies. Gullies can affect also whole localities (e.g. Calonda, in Lunda Norte, Angola), destroying paved houses, roads and other infrastructures. Because of this, much effort is invested into the study of gullies within the scope of geomorphology, namely in what concerns in the prevention of gully erosion and in the restoration of gullied landscapes.
Gully erosion represents an important sediment source in river systems and accounts for as much as 70 to 90% of the overall sediment production of a catchment. In mountain areas, the steep slopes enhance gully processes, accelerate sediment transfer from uplands to valley bottoms and generate natural hazards: mudflows, overflowing of heavily loaded floods, silting up of reservoirs, for example.
The cache will lead you to a beautifull scenario, Monte da Lua, where the gullying process is clearly visible (Monte da Lua, Moon Hill, would be a clearly appropriate designation had not current water been the cause of the process...). The wide grain size distribution of the fomrations' sediments (larger stones acting as caps of finer grains) is in the basis of a scenic bonus, the hoodoos (fairy chimneys), a by-product of the gullying process.
To claim the cache, on the PZ facing south, you have to answer this questions:
How many beds can you see?
What is the thickness of the first bed (top)?
What is the color and texture of the first bed?
Take a picture of you with MrGPS, where we can also see the gullying.
Mail me the answers, and after permission, make your log and upload your picture.
Esta cache leva-o a um magnífico miradouro denominado Monte da Lua. Aqui podem ser observados os efeitos sobre a topografia do fenómeno "ravinamento".
Para reclamar esta cache, coloque-se no PZ, observe a ravina a Sul e responda às seguintes questões:
Quantas camadas distintas compõem a ravina?
Qual a espessura da primeira camada?
Qual a cor e a textura da primeira camada?
Tire uma fotografia sua com o MrGPS, onde seja possível visualizar também a ravina.
Envia-me as respostas por mail, e após autorização faça o seu log e o upload da fotografia exigida.