Географски разгледи (47) 5-10 (2013) 5

УДК: 551.435(497.7)

WEATHERING MICRO-FORMS ON VERTICAL ROCK SIDES IN THE REPUBLIC OF MACEDONIA - BRIEF REMARKS

Blagoja MARKOSKI, Ivica MILEVSKI Institute of Geography, Faculty of Science, Skopje e-mail: ivicamilevski@gmail.com

ABSTRACT

In the mountain landscape of the Republic of Macedonia, frequent phenomena of weathering microforms in exposed rocks appear. Some of them are created on horizontal rock surfaces, but there are mountain sites with interesting small wea-thering forms on vertical rock surface. In this paper, the prevalence and genesis of this kind of weathering forms seen in the Republic of Macedonia is analyzed. Fac-tors such as petrographic and mineralogical composition of the rocks, climatic and biotic factors as well as human impact are considered. The explanations for the genesis of micro forms of vertical rock surfaces have purely scientific significance, but these forms are unique and attract attention and interest among tourists. Fur-thermore, several sites with that kind of landforms are reviewed as a potential geo-sites and geoparks. Therefore, varieties of methods are used to clarify the origin of small weathering forms on a vertical surface.

Key words: weathering, micro-forms, denudation, vertical rocks

INTRODUCTION In the landscape of the Republic of Macedonia, frequent phenomena of

weathering microforms in exposed rocks appear. Some of them are created on horizontal rock surfaces, but there are sites with interesting small wea-thering forms on vertical rock surfaces. Vertical rock surfaces are usually finds on builders, stones, blocks, escarpments and similar formations with vertical or nearly vertical sides. There are several geomorphological re-searches and papers which elaborated morphology and origin of these stones in Macedonia in detail. Its authors concluded that these stones ap-

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pear mostly as a product of long-term weathering (denudation, erosion) of different rocks.

In this paper, the prevalence and genesis of this kind of weathering forms seen in the Republic of Macedonia is analyzed. Factors such as pe-trographic and mineralogical composition of the rocks, climatic and biotic factors as well as human impact are considered. The explanations for the genesis of micro forms of vertical rock surfaces have purely scientific sig-nificance, but these forms are unique and attract attention and interest among tourists. Furthermore, several sites with that kind of landforms are reviewed as a potential geosites and geoparks. Therefore, varieties of me-thods are used to clarify the origin of small weathering forms on a vertical surface.

In this study of the genesis of micro forms on vertical rocks, several cabinet and field methods are used. Particularly preferred was the method of direct field observation, analysis and comparison of the factors affecting the formation of micro-relief forms. Area of interest is Baba Mountain, Selečka Mountain, Nidže Mountain, Mariovo and Kozjačija region near Kumanovo.

SITES LOCATION The aforementioned genetic factors forming micro forms in the vertical

surface of the rocks exactly coincide with the characteristics of petrograph-ic and mineralogical composition, climatic and vegetation features that are present on particular site. Particularly characteristic is Pelagonian region where mountains Baba, Selecka and Dren are characterized by metamor-phic sedimentary rocks such as loathsome, mica-schist, conglomerates, breccias, etc. These mountains are relatively small in terms of height Pela-gonian Plain, Basin and Babuna Mariovo area where winter prevails in the presence of fog and increased humidity in the summer with low humidity and the presence of rainfall convection hot air from surrounding basins. Also Propagation height fog in winter equated with heights of the moun-tains where the air mass flow (exchange of air masses between the basins above) comes to the fore in the context of the breakdown of rocks and for-mation of caverns in the vertical surface of the rocks. Similar conditions are in Kozjačija near Kumanovo where in the valley widening between Pčinja and Kriva Reka are stationed moist air masses in the winter and present dry and hot summers, with low vegetation, so that form these shapes. The for-mations on vertical rock surfaces on the Nidze Mountain are slightly differ-ent. It is a higher mountain areas where the move permanent grasslands occurring air currents due to climate impacts and significant differences of southern and northern slopes of the mountain. Examples with less pro-

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nounced these forms are find and elsewhere in the Republic Macedonia, but they deserve special attention.

FACTORS OF GENESIS The listed areas have particular petrographic and mineralogical compo-

sition, specific relief position in relation to neighboring valleys and plains and specific climatic and vegetation characteristics. In these geographic features, the main factors in the genesis of micro-relief forms of vertical rock surfaces are included as follows:

• petrographic mineralogical composition of rocks, • physical, chemical and biogenic breakdown of rocks, • climatic peculiarities in specific regions and • biogenic factors. Petrographic and mineralogical composition of the rocks is one of the

most important factors. Based on geological data, field research and obser-vations, these forms are generally found in metamorphic and sedimentary rocks (gneiss, mica-schist, phyllites, sandstones, etc.), while in igneous rocks rarely occur. The reason for this is in poorly connected heterogeneous minerals, so that the processes of decomposition of rocks are significant.

Fig. 1, Micro forms in vertical granodioritic rocks on Markovi Kuli site north of Prilep.

Rock weathering is a critical factor. Impacts are based on different le-

vels of heating and cooling of different minerals within the rocks (darker,

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brighter, firmer and softer, less soluble, more soluble minerals). Under such conditions, rock surface is under weathering, and vertical surface cause fast gravitational fall of eroded mineral grains. In contrary the situation is much different on horizontal rock surfaces mainly overgrown with lichen, moss and grass that in some degree protect these surfaces from the impact of in-solation, wind and water erosion. This situation is greatly influenced by other climatic factors as the temperature, humidity and wind effects. In conditions of low temperatures and increased humidity due to the frequent autumn-to-winter fogs in these areas, it comes to freezing of water droplets on the rock surface increasing and further weathering of the rocks. Field research shows as partly or fully decomposed, shallow rock layers (1-5 mm thick) slowly fall toward the base of the rocks.

Additionally on highly exposed and unprotected vertical rock surfaces, wind action has strong effect thus weathering and transport of eroded ma-terial is even more intense. Also, strong winds move and accelerate small rock particles which blow into rock surface thus increasing erosion effect.

Fig. 2, Small and micro forms in gneiss rocks.

The weathering process in vertical rocks is frequently supported by lack of vegetation. Areas in the vicinity of such forms are covered with grass-lands and bushes, while forests are usually absent or represented by indi-vidual trees. Thus, the lack of vegetation allows strong winds action of air masses on the one hand cleaning mid and pre-cooling rocky surface, and on the other side humidity that is present in the near environment, ie in the plains (eg, Pelagonian plain) quickly condenses and freezes. In the process of the creation of micro forms on the vertical rock surface certain influence

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of small animals, especially insects are observed also. Notably, some of the caverns formed on the vertical surfaces of observed rocks some insects in search of lee-slopes (more-protected places) build clay deposits in perform-ing propagation. Such works usually take place during the warm part of the year due to thermal processes occurring decomposition of mineral ingre-dients. During the wet periods, clay creations get wet, heavier and fall-down with parts of subsoil. In that way continuous deepening of micro-relief forms occurs.

CONCLUSION Based on long-term field observations, analysis and comparisons, in the

Republic of Macedonia several sites with numerous weathering forms in vertical rocks are recognized. Genesis of these forms is explained by severe weathering in highly exposed rocks with particular mineral composition. The main factors are physical, chemical and biogenic disintegration of rocks; climatic peculiarities in specific regions and some biogenic factors.

It was concluded that this type of weathering micro forms on the vertical rock surface occurs mainly in metamorphic rocks and less in sedimentary rocks. Especially strong is the influence of physical breakdown (tempera-ture amplitude, ice weathering etc.) coupled with the impact of the air masses flow, especially in open space with strong winds. In the creation of such forms zoogenic impact is established also. Namely, in the vertical sur-faces of observed rocks, some insects in search of lee sides protected from winds, deepen caverns and build clay deposits in performing breeding. They do that in the summer, but through the winter due to increased humid-ity clay deposit weigh increase, pulling-down detached mineral grains from the lee surface. Such phenomena have been observed mainly in areas where winter winds are rare or weak and valley bottoms or depressions are foggy. Typical example are hillsides of Babuna Mountain with Zlatovrv and Selečka Mountain where the Pelagonian plain and Mariovo fog and hill-sides between them negligible flow of air masses. Some other landscapes with similar features (for example Mangovica Mountain between Ovče Pole and Kočani depression) but with strong to severe winds throughout the year, small weathering forms on vertical rock surface are not recorded.

REFERENCES

VGI (1972-75): Topographic maps 1:25000, Beograd. Маркоски Б. (1992): Картографско картометриски проучувања на хипсомет-

риската струкрура на просторот и разместеноста на населението во Република Македонија, докторска дисертација одбранета на институтот за географија при ПМФ, Скопје. (ракопис).

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Маркоски Б. (1995): Хипсометрија на просторот и населеноста во Република Македонија - картографски метод. Македонска ризница - Куманово.

Маркоски Б., Колчакоски Д., Василески Д., Матески В., Костадиноски М., Меловски Љ., Христовски С. (2003): Карта на природното богатство на Република Македонија (размер 1:200000, Зборник на трудови, Втор конгрес на еколозите од Република Македонија, кн. 2, Скопје.

Маркоски Б. (1985-2012): Теренски истражувања и опсервации.

МИКРОРЕЛЈЕФНИ ОБЛИЦИ НА ВЕРТИКАЛНА КАРПЕСТА ОСНОВА

Благоја Маркоски, Ивица Милевски

И З В О Д

На планината Бабуна, Селечка Планина, областа Мариово, на планината

Ниџе и во областа Козјачија и СТрацин во Кумановско се идентификувани различни денудациски микрорелјефни форми на вертикална карпеста основа. Констатирано е дека ваков тип форми настанува главно на метаморфни карпи, а помалку на седиментни и магматски карпи. Особено е влијанието на физичкото распаѓање (температурни влијанија, амплитуди, мразно распаѓање и сл.) потпомогнато влијанието на струењето на воздушните маси (кои не мора секогаш да бидат со силен интензитет. Во формирањето на ваквите облици е констатирано и зоогено влијание. Имено, на вертикалните површи-ни на карпите се забележани одредени инсекти кои во потрага на заветрина (позашѕитени места) градат глинени лежишта во кои вршат размножување. Тоа го прават во лето, а преку зимскиот период поради зголемената влажност глината натежнува и се одлепува повлекувајќи и минерални зрна од матич-ниот супстрат.

Вакви појави се забележани главно во териториите каде во зимскиот пе-риод од годината во котлинските дна има магли а на возвишенијата незна-чителни воздушни стуења. Типичен пример се возвишенијата на планината Бабуна и Селечка Планина каде во Пелагониската рамница и Мариово има магли а на возвишенијата помеѓу нив незначително струење на воздушните маси. Во пределите кои се со слични релјефни карактеристики приме пла-нината Манговица помеѓу Овче Поле и Кочанска Котлина каде интензитетот на ветерот е можне силен скоро низ целиот период од годината микрорелјеф-ни форми на вертикална карпеста основа не се забележани.