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Thunder mountain / Hromova hora

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Hidden : 09/09/2009
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Geocache Description:

Milesovka (in German Milleschauer, Donnersberg) is the highest peak of Ceske Stredohori, Czech Republic.

Since 1903, the meteorological observatory (which is oldest Czech mountain station) is situated on its top reaching 836,5m a.s.l., together with the outlook-tower.


This mountain has almost same geological origin as the rest of phonolite cones of Ceske Stredohori. According to geochronological studies, the age of Milesovka is 27-31,5 millions years. It means that the body of this mountain was formed during the main volcanic stage of the creation of Ceske Stredohori. In the geological maps and guides we read that the basic material from which the mountain is formed is sodalitic trachyte. In principle, it is a kind of phonolite having higher content of potassium feldspar and soda-lime feldspar. It is probable that the mountain has been formed from the subsurface body consisting of very viscous magma squeezed through the fractures in the earth's crust into subsurface layers where it formed dome-shaped formation. By its volume, which represents 60 millions m3 ( only the portion protruding above 600m a.s.l.), the mountain is largest phonolitic body far and wide. The phonolites from Milesovka are exhibiting characteristic mural jointing the material is slacking into relatively thin plates having uneven surfaces. The stony fields consisting of such plates are abundant on phonolitic hills. You may encounter the trachytic plates also on Milesovka mountain, especially near to its summit. The mural jointing follows the isothermal faces of cooled down magma. Thus its structure reminds the coats of an onion.

The minerals and fossils: The mountain as such is not considered to be a mineralogical or palaeontologic locality. The structural rock - grey-green sodalitic trachyte consisting mainly of microcrystals of alkalic feldspars with sodalite inclusions and phenocrysts (macroscopic perspicuous crystals) of sanidine (also alkalic feldspar) with little content of dark minerals, mainly green egirine.

Your log will be accepted if you visit the locality and fulfil following tasks:
- take a photo showing you with your GPS with view from Milesovka at east or south and attach it to the log
- answer following questions:
1. which chemical elements are absent in the phonolite from Milesovka in comparison with other hills in the vicinity?
2. which protected plants may be found on Milesovka?
3. which year was Milesovka declared as national reserve?
4. how Alexander von Humboldt classified the view from the top of Milešovka?



Milesovka (nemecky Milleschauer, Donnersberg) je nejvyssi hora Ceskeho stredohori. Jeji vrchol lezi ve vysce 836,5 metru nad morem. Od roku 1903 zdobi jeji vrchol vyhlidkova vez a meteorologicka observator, ktera je nejstarsi horskou meteorologickou stanici na nasem uzemi.

Hora Milesovka se svym geologickym puvodem prilis nelisi od ostatnich znelcovych kopcu Ceskeho stredohori. Absolutni datovani ukazuje na stari 27-31.5 milionu let, vznik telesa Milesovky tedy spada do hlavni vulkanicke faze vzniku Ceskeho stredohori. Geologicke mapy a pruvodce uvadeji jako nazev horniny, kterou je hora tvorena, sodaliticky trachyt. Jedna se v podstate o znelec s vetsim podilem draselneho i sodnovapenateho zivce. V dobe vzniku pravdepodobne podpovrchoveho telesa se tedy jednalo o znacne vazke magma, ktere bylo podel trhlin v zemske kure vtlaceno do podpovrchovych vrstev v podobe kopuloviteho utvaru. Svym objemem, ktery presahuje jen nad urovni 600 m.n.m. 60 milionu metru krychlovych je Milesovka siroko daleko nejvetsim znelcovym telesem. Typickym priznakem znelcu, zretelnym i na Milesovce, je deskovita odlucnost, projevujici se v rozpadu horniny na relativne tenke desky s nerovnym povrchem. Sutova pole s takovymi deskami jsou na znelcovych kopcich bezna a obzvlaste ve vrcholovych partiich Milesovky se s deskami trachytu setkate. Deskovita odlucnost sleduje plochy stejne rychleho chladnuti magmatu a proto je na telese vyvinuta podobne jako slupky na cibuli.

Mineraly a fosilie : Samotna hora neni povazovana ani za mineralogickou ani paleontologickou lokalitu. Vlastni hornina, sedozelenavy sodaliticky trachyt je tvoren prevazne mikrokrystaly alkalickych zivcu s primesi sodalitu, vyrostlicemi (makroskopicky zretelnymi krystaly) sanidinu, rovnez alkalickeho zivce a s malym podilem tmavych mineralu hlavne zeleneho egirinu.

K uznani logu musite navstivit tuto lokalitu a splnit nasledujici ukoly:
- k logu pridejte fotografii Vas a pristroje GPS s vyhledem z Milesovky na vychod, nebo jih
- odpovedet na otazky, jejichž odpovedi mi zašlete pres profil:
1. absenci kterych chemickych prvku se Milesovka lisi od jinych znelcu v okoli?
2. ktere chranene rostliny je mozne na Milesovce videt?
3. od ktereho roku je Milesovka rezervaci?
4. jak oznacil Alexander von Humboldt vyhled z Milesovky?


S odpovedmi vam muzou pomoci nasledujici odkazy:
Bilinska prirodovedna spolecnost
Milesovka na Wikipedii
Memorial Svati Pulce

Additional Hints (Decrypt)

Bqcbirqv cebfíz aruáqrwgr, wfbh x mwvšgraí anceíxynq v mqr hirqraýpu bqxnmrpu.

Decryption Key


(letter above equals below, and vice versa)



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