Polar climate
The polar climate regions are characterized by a lack of warm summers. Every month in a polar climate has an average temperature of less than 10 °C. Regions with polar climate cover more than 20% of the Earth. Most of these regions are far from the equator, in this case, winter days are short and summer days are long. A polar climate consists of cool summers and cold winters, which results in treeless tundra, glaciers, or a permanent or semi-permanent layer of ice. There are two types of polar climate: tundra climate. A tundra climate is characterized by having at least one month whose average temperature is above 0 °C, while an ice cap climate has no months above 0 °C. In a tundra climate, trees can not grow. In an ice cap climate, no plants can grow, ice accumulates until it flows elsewhere. Many high altitude locations on Earth have a climate where no month has an average temperature of 10 °C or higher, but as this is due to elevation, this climate is referred to as Alpine climate. Alpine climate can mimic either ice cap climate.
On Earth, the only continent where the ice cap polar climate is predominant is Antarctica. All but a few isolated coastal areas on the island of Greenland have the ice cap climate. Coastal regions of Greenland that do not have permanent ice sheets have the less extreme tundra climates; the northernmost part of the Eurasian land mass, from the extreme northeastern coast of Scandinavia and eastwards to the Bering Strait, large areas of northern Siberia and northern Iceland have tundra climate as well. Large areas in northern Canada and northern Alaska have tundra climate, changing to ice cap climate in the most northern parts of Canada. Southernmost South America and such subantarctic islands such as the South Shetland Islands and the Falkland Islands have tundra climates of slight thermal range in which no month is as warm as 10 °C; these subantarctic lowlands are found closer to the equator than the coastal tundras of the Arctic basin. Some parts of the Arctic are covered by ice year-round, nearly all parts of the Arctic experience long periods with some form of ice on the surface.
Average January temperatures range from about −40 to 0 °C, winter temperatures can drop below −50 °C over large parts of the Arctic. Average July temperatures range from about −10 to 10 °C, with some land areas exceeding 30 °C in summer; the Arctic consists of ocean, surrounded by land. As such, the climate of much of the Arctic is moderated by the ocean water, which can never have a temperature below −2 °C. In winter, this warm water though covered by the polar ice pack, keeps the North Pole from being the coldest place in the Northern Hemisphere, it is part of the reason that Antarctica is so much colder than the Arctic. In summer, the presence of the nearby water keeps coastal areas from warming as much as they might otherwise, just as it does in temperate regions with maritime climates; the climate of Antarctica is the coldest on Earth. Antarctica has the lowest occurring temperature recorded: −89.2 °C at Vostok Station. It is extremely dry, averaging 166 millimetres of precipitation per year, as weather fronts penetrate far into the continent.
There have been several attempts at quantifying. Climatologist Wladimir Köppen demonstrated a relationship between the Arctic and Antarctic tree lines and the 10 °C summer isotherm. See Köppen climate classification for more information. Otto Nordenskjöld theorized that winter conditions play a role: His formula is W = 9 − 0.1 C, where W is the average temperature in the warmest month and C the average of the coldest month, both in degrees Celsius. For example, if a particular location had an average temperature of −20 °C in its coldest month, the warmest month would need to average 11 °C or higher for trees to be able to survive there as 9 − 0.1 = 11. Nordenskiöld's line tends to run to the north of Köppen's near the west coasts of the Northern Hemisphere continents, south of it in the interior sections, at about the same latitude along the east coasts of both Asia and North America. In the Southern Hemisphere, all of Tierra del Fuego lies outside the polar region in Nordenskiöld's system, but part of the island is reckoned as being within the Antarctic under Köppen's.
In 1947, Holdridge improved on these schemes, by defining biotemperature: the mean annual temperature, where all temperatures below 0 °C or 32 °F are treated as 0 °C. If the mean biotemperature is between 1.5 and 3 °C, Holdridge quantifies the climate as subpolar. Arctic oscillation Köppen climate classification NOAA State of the Arctic Report 2006
Pleistocene
The Pleistocene is the geological epoch which lasted from about 2,588,000 to 11,700 years ago, spanning the world's most recent period of repeated glaciations. The end of the Pleistocene corresponds with the end of the last glacial period and with the end of the Paleolithic age used in archaeology; the Pleistocene is the first epoch of the Quaternary Period or sixth epoch of the Cenozoic Era. In the ICS timescale, the Pleistocene is divided into four stages or ages, the Gelasian, Middle Pleistocene and Upper Pleistocene. In addition to this international subdivision, various regional subdivisions are used. Before a change confirmed in 2009 by the International Union of Geological Sciences, the time boundary between the Pleistocene and the preceding Pliocene was regarded as being at 1.806 million years Before Present, as opposed to the accepted 2.588 million years BP: publications from the preceding years may use either definition of the period. Charles Lyell introduced the term "Pleistocene" in 1839 to describe strata in Sicily that had at least 70% of their molluscan fauna still living today.
This distinguished it from the older Pliocene epoch, which Lyell had thought to be the youngest fossil rock layer. He constructed the name "Pleistocene" from the Greek πλεῖστος, pleīstos, "most", καινός, kainós, "new"; the Pleistocene has been dated from 2.588 million to 11,700 years BP with the end date expressed in radiocarbon years as 10,000 carbon-14 years BP. It covers most of the latest period of repeated glaciation, up to and including the Younger Dryas cold spell; the end of the Younger Dryas has been dated to about 9640 BC. The end of the Younger Dryas is the official start of the current Holocene Epoch. Although it is considered an epoch, the Holocene is not different from previous interglacial intervals within the Pleistocene, it was not until after the development of radiocarbon dating, that Pleistocene archaeological excavations shifted to stratified caves and rock-shelters as opposed to open-air river-terrace sites. In 2009 the International Union of Geological Sciences confirmed a change in time period for the Pleistocene, changing the start date from 1.806 to 2.588 million years BP, accepted the base of the Gelasian as the base of the Pleistocene, namely the base of the Monte San Nicola GSSP.
The IUGS has yet to approve a type section, Global Boundary Stratotype Section and Point, for the upper Pleistocene/Holocene boundary. The proposed section is the North Greenland Ice Core Project ice core 75° 06' N 42° 18' W; the lower boundary of the Pleistocene Series is formally defined magnetostratigraphically as the base of the Matuyama chronozone, isotopic stage 103. Above this point there are notable extinctions of the calcareous nanofossils: Discoaster pentaradiatus and Discoaster surculus; the Pleistocene covers the recent period of repeated glaciations. The name Plio-Pleistocene has, in the past, been used to mean the last ice age; the revised definition of the Quaternary, by pushing back the start date of the Pleistocene to 2.58 Ma, results in the inclusion of all the recent repeated glaciations within the Pleistocene. The modern continents were at their present positions during the Pleistocene, the plates upon which they sit having moved no more than 100 km relative to each other since the beginning of the period.
According to Mark Lynas, the Pleistocene's overall climate could be characterized as a continuous El Niño with trade winds in the south Pacific weakening or heading east, warm air rising near Peru, warm water spreading from the west Pacific and the Indian Ocean to the east Pacific, other El Niño markers. Pleistocene climate was marked by repeated glacial cycles in which continental glaciers pushed to the 40th parallel in some places, it is estimated. In addition, a zone of permafrost stretched southward from the edge of the glacial sheet, a few hundred kilometres in North America, several hundred in Eurasia; the mean annual temperature at the edge of the ice was −6 °C. Each glacial advance tied up huge volumes of water in continental ice sheets 1,500 to 3,000 metres thick, resulting in temporary sea-level drops of 100 metres or more over the entire surface of the Earth. During interglacial times, such as at present, drowned coastlines were common, mitigated by isostatic or other emergent motion of some regions.
The effects of glaciation were global. Antarctica was ice-bound throughout the Pleistocene as well as the preceding Pliocene; the Andes were covered in the south by the Patagonian ice cap. There were glaciers in New Tasmania; the current decaying glaciers of Mount Kenya, Mount Kilimanjaro, the Ruwenzori Range in east and central Africa were larger. Glaciers existed to the west in the Atlas mountains. In the northern hemisphere, many glaciers fused into one; the Cordilleran ice sheet covered the North American northwest. The Fenno-Scandian ice sheet rested including much of Great Britain. Scattered domes stretched across Siberi
Permafrost
In geology, permafrost is ground, including rock or soil, at or below the freezing point of water 0 °C for two or more years. Most permafrost is located in high latitudes, but at lower latitudes alpine permafrost occurs at higher elevations. Ground ice is not always present, as may be in the case of non-porous bedrock, but it occurs and it may be in amounts exceeding the potential hydraulic saturation of the ground material. Permafrost accounts for 0.022% of total water on Earth and the permafrost region covers 24% of exposed land in the Northern Hemisphere. It occurs subsea on the continental shelves of the continents surrounding the Arctic Ocean, portions of which were exposed during the last glacial period; the thawing of permafrost has implications for the global climate. A global temperature rise of 1.5 °C above current levels would be enough to start the thawing of permafrost in Siberia, according to one group of scientists. "In contrast to the relative dearth of reports on frozen ground in north America prior to World War II, a vast literature on the engineering aspects of permafrost was available in Russian.
Beginning in 1942, Siemon William Muller delved into the relevant Russian literature held by the Library of Congress and the U. S. Geological Survey Library so that he was able to furnish the government an engineering field guide and a technical report about permafrost by 1943", year in which he coined the term as a contraction of permamently frozen ground. Although classified, in 1947 a revised report was released publicly, regarded as the first North American treatise on the subject. Permafrost is soil, rock or sediment, frozen for more than two consecutive years. In areas not overlain by ice, it exists beneath a layer of soil, rock or sediment, which freezes and thaws annually and is called the "active layer". In practice, this means that permafrost occurs at an mean annual temperature of − 2 colder. Active layer thickness is 0.3 to 4 meters thick. The extent of permafrost varies with the climate: in the Northern Hemisphere today, 24% of the ice-free land area, equivalent to 19 million square kilometers, is more or less influenced by permafrost.
Of this area more than half is underlain by continuous permafrost, around 20 percent by discontinuous permafrost, a little less than 30 percent by sporadic permafrost. Most of this area is found in Siberia, northern Canada and Greenland. Beneath the active layer annual temperature swings of permafrost become smaller with depth; the deepest depth of permafrost occurs. Above that bottom limit there may be permafrost, whose temperature doesn't change annually—"isothermal permafrost". Permafrost forms in any climate where the mean annual air temperature is less than the freezing point of water. Exceptions are found in moist-wintered forest climates, such as in Northern Scandinavia and the North-Eastern part of European Russia west of the Urals, where snow acts as an insulating blanket. Glaciated areas may be exceptions. Since all glaciers are warmed at their base by geothermal heat, temperate glaciers, which are near the pressure-melting point throughout, may have liquid water at the interface with the ground and are therefore free of underlying permafrost.
"Fossil" cold anomalies in the Geothermal gradient in areas where deep permafrost developed during the Pleistocene persist down to several hundred metres. This is evident from temperature measurements in boreholes in North Europe; the below-ground temperature varies less from season to season than the air temperature, with mean annual temperatures tending to increase with depth as a result of the geothermal crustal gradient. Thus, if the mean annual air temperature is only below 0 °C, permafrost will form only in spots that are sheltered—usually with a northerly aspect—creating discontinuous permafrost. Permafrost will remain discontinuous in a climate where the mean annual soil surface temperature is between −5 and 0 °C. In the moist-wintered areas mentioned before, there may not be discontinuous permafrost down to −2 °C. Discontinuous permafrost is further divided into extensive discontinuous permafrost, where permafrost covers between 50 and 90 percent of the landscape and is found in areas with mean annual temperatures between −2 and −4 °C, sporadic permafrost, where permafrost cover is less than 50 percent of the landscape and occurs at mean annual temperatures between 0 and −2 °C.
In soil science, the sporadic permafrost zone is abbreviated SPZ and the extensive discontinuous permafrost zone DPZ. Exceptions occur in un-glaciated Siberia and Alaska where the present depth of permafrost is a relic of climatic conditions during glacial ages where winters were up to 11 °C colder than those of today. At mean annual soil surface temperatures below −5 °C the influence of aspect can never be sufficient to thaw permafrost and a zone of continuous permafrost forms. A line of continuous permafrost in the Northern Hemisphere represents the most southerly border where land is covered by continuous permafrost or glacial ice; the line of continuous permafrost varies around the world northward or southward due to regional climatic changes. In the southern hemisphere, most of the equivalent line would fall within the Southern Ocean if there were land there. Most of the Antarctic continent is overl
Alps
The Alps are the highest and most extensive mountain range system that lies in Europe, separating Southern from Central and Western Europe and stretching 1,200 kilometres across eight Alpine countries: France, Italy, Liechtenstein, Austria and Slovenia. The mountains were formed over tens of millions of years as the African and Eurasian tectonic plates collided. Extreme shortening caused by the event resulted in marine sedimentary rocks rising by thrusting and folding into high mountain peaks such as Mont Blanc and the Matterhorn. Mont Blanc spans the French–Italian border, at 4,810 m is the highest mountain in the Alps; the Alpine region area contains about a hundred peaks higher than 4,000 metres. The altitude and size of the range affects the climate in Europe. Wildlife such as ibex live in the higher peaks to elevations of 3,400 m, plants such as Edelweiss grow in rocky areas in lower elevations as well as in higher elevations. Evidence of human habitation in the Alps goes back to the Palaeolithic era.
A mummified man, determined to be 5,000 years old, was discovered on a glacier at the Austrian–Italian border in 1991. By the 6th century BC, the Celtic La Tène culture was well established. Hannibal famously crossed the Alps with a herd of elephants, the Romans had settlements in the region. In 1800, Napoleon crossed one of the mountain passes with an army of 40,000; the 18th and 19th centuries saw an influx of naturalists and artists, in particular, the Romantics, followed by the golden age of alpinism as mountaineers began to ascend the peaks. The Alpine region has a strong cultural identity; the traditional culture of farming and woodworking still exists in Alpine villages, although the tourist industry began to grow early in the 20th century and expanded after World War II to become the dominant industry by the end of the century. The Winter Olympic Games have been hosted in the Swiss, Italian and German Alps. At present, the region has 120 million annual visitors; the English word Alps derives from the Latin Alpes.
Maurus Servius Honoratus, an ancient commentator of Virgil, says in his commentary that all high mountains are called Alpes by Celts. The term may be common to Italo-Celtic, because the Celtic languages have terms for high mountains derived from alp; this may be consistent with the theory. According to the Oxford English Dictionary, the Latin Alpes might derive from a pre-Indo-European word *alb "hill". Albania, a name not native to the region known as the country of Albania, has been used as a name for a number of mountainous areas across Europe. In Roman times, "Albania" was a name for the eastern Caucasus, while in the English languages "Albania" was used as a name for Scotland, although it is more derived from the Latin albus, the color white; the Latin word Alpes could come from the adjective albus. In modern languages the term alp, albe or alpe refers to a grazing pastures in the alpine regions below the glaciers, not the peaks. An alp refers to a high mountain pasture where cows are taken to be grazed during the summer months and where hay barns can be found, the term "the Alps", referring to the mountains, is a misnomer.
The term for the mountain peaks varies by nation and language: words such as Horn, Kopf, Spitze and Berg are used in German speaking regions. The Alps are a crescent shaped geographic feature of central Europe that ranges in a 800 km arc from east to west and is 200 km in width; the mean height of the mountain peaks is 2.5 km. The range stretches from the Mediterranean Sea north above the Po basin, extending through France from Grenoble, stretching eastward through mid and southern Switzerland; the range continues onward toward Vienna and east to the Adriatic Sea and Slovenia. To the south it dips into northern Italy and to the north extends to the southern border of Bavaria in Germany. In areas like Chiasso and Allgäu, the demarcation between the mountain range and the flatlands are clear; the countries with the greatest alpine territory are Austria, Italy and Switzerland. The highest portion of the range is divided by the glacial trough of the Rhône valley, from Mont Blanc to the Matterhorn and Monte Rosa on the southern side, the Bernese Alps on the northern.
The peaks in the easterly portion of the range, in Austria and Slovenia, are smaller than those in the central and western portions. The variances in nomenclature in the region spanned by the Alps makes classification of the mountains and subregions difficult, but a general classification is that of the Eastern Alps and Western Alps with the divide between the two occurring in eastern Switzerland according to geologist Stefan Schmid, near the Splügen Pass; the highest peaks of the Western Alps and Eastern Alps are Mont Blanc, at 4,810 m and Piz Bernina at 4,049 metres. The second-highest major
Loess
Loess is a clastic, predominantly silt-sized sediment, formed by the accumulation of wind-blown dust. Ten percent of the Earth's land area is covered by similar deposits. Loess is an aeolian sediment formed by the accumulation of wind-blown silt in the 20–50 micrometer size range, twenty percent or less clay and the balance equal parts sand and silt that are loosely cemented by calcium carbonate, it is homogeneous and porous and is traversed by vertical capillaries that permit the sediment to fracture and form vertical bluffs. The word loess, with connotations of origin by wind-deposited accumulation, came into English from German Löss, which can be traced back to Swiss German and is cognate with the English word loose and the German word los, it was first applied to Rhine River valley loess about 1821. Loess is homogeneous, friable, pale yellow or buff coherent non-stratified and calcareous. Loess grains are angular with little polishing or rounding and composed of crystals of quartz, feldspar and other minerals.
Loess can be described as a dust-like soil. Loess deposits may become thick, more than a hundred meters in areas of China and tens of meters in parts of the Midwestern United States, it occurs as a blanket deposit that covers areas of hundreds of square kilometers and tens of meters thick. Loess stands in either steep or vertical faces; because the grains are angular, loess will stand in banks for many years without slumping. This soil has a characteristic called vertical cleavage which makes it excavated to form cave dwellings, a popular method of making human habitations in some parts of China. Loess will erode readily. In several areas of the world, loess ridges have formed that are aligned with the prevailing winds during the last glacial maximum; these are called "paha ridges" in "greda ridges" in Europe. The form of these loess dunes has been explained by a combination of tundra conditions. Loess comes from the German Löss or Löß, from Alemannic lösch meaning drop as named by peasants and masons along the Rhine Valley.
The term "Löß" was first described in Central Europe by Karl Cäsar von Leonhard who reported yellowish brown, silty deposits along the Rhine valley near Heidelberg. Charles Lyell brought this term into widespread usage by observing similarities between loess and loess derivatives along the loess bluffs in the Rhine and Mississippi. At that time it was thought that the yellowish brown silt-rich sediment was of fluvial origin being deposited by the large rivers, it wasn't until the end of the 19th century that the aeolian origin of loess was recognized the convincing observations of loess in China by Ferdinand von Richthofen. A tremendous number of papers have been published since focusing on the formation of loess and on loess/palaeosol sequences as archives of climate and environment change; these water conservation works were carried out extensively in China and the research of Loess in China has been continued since 1954. Much effort was put into the setting up of regional and local loess stratigraphies and their correlation.
But the chronostratigraphical position of the last interglacial soil correlating to marine isotope substage 5e has been a matter of debate, owing to the lack of robust and reliable numerical dating, as summarized for example in Zöller et al. and Frechen, Horváth & Gábris for the Austrian and Hungarian loess stratigraphy, respectively. Since the 1980s, thermoluminescence, optically stimulated luminescence and infrared stimulated luminescence dating are available providing the possibility for dating the time of loess deposition, i.e. the time elapsed since the last exposure of the mineral grains to daylight. During the past decade, luminescence dating has improved by new methodological improvements the development of single aliquot regenerative protocols resulting in reliable ages with an accuracy of up to 5 and 10% for the last glacial record. More luminescence dating has become a robust dating technique for penultimate and antepenultimate glacial loess allowing for a reliable correlation of loess/palaeosol sequences for at least the last two interglacial/glacial cycles throughout Europe and the Northern Hemisphere.
Furthermore, the numerical dating provides the basis for quantitative loess research applying more sophisticated methods to determine and understand high-resolution proxy data, such as the palaeodust content of the atmosphere, variations of the atmospheric circulation patterns and wind systems, palaeoprecipitation and palaeotemperature. According to Pye, four fundamental requirements are necessary for the formation of loess: a dust source, adequate wind energy to transport the dust, a suitable accumulation area, a sufficient amount of time. Periglacial loess is derived from the floodplains of glacial braided rivers that carried large volumes of glacial meltwater and sediments from the annual melting of continental icesheets and mountain icecaps during the spring and summer. During the autumn and winter, when melting of the icesheets and icecaps ceased, the flow of meltwater down these rivers either ceased or was reduced; as a consequence, large parts of the submerged and unvegetated floodplains of these braided rivers dried out and were exposed to the wind.
Because these floodplains consist of sediment containing a high content of glacial
Paha (landform)
Paha are landforms composed of prominent hills that are oriented from northwest to southeast and have large loess deposits. They developed during the period of mass erosion that developed the Iowan surface, are considered erosional remnants and are at interstream divides. Paha rise above the surrounding landscape more than 20 feet; the word paha means hill in Dakota Sioux. A well known Paha is the hill on which the town of Iowa developed. An early theory of the origin of the paha hills of Iowa described them as "composed in part of water-laid sand and silt and in part of ice-molded till". After it came to be understood that loess soil was wind deposited silt, pahas came to be interpreted as a kind of sand dune. "Their persistent southeasterly trend hypothetically suggested deposition of the loess by prevailing northwesterly winds blowing south of the continental ice sheet." The modern explanation is that the shape of pahas is the result of the permafrost conditions that dominated glacial till plains of the Iowan surface during the last ice age.
Permafrost effects controlled both the way this surface eroded and the way loess accumulated on this surface.. One recent hypothesis attempts to account for the paha as being remnants of interstream divides by attributing snowmelt-erosion as the agent caused by NW-SE, parallel snowdunes that were transverse to an anticyclonic wind system hovering over the continental ice sheet; this was contemporaneous with snowmelt-erosion caused by blankets of snow flattening out the terrain surrounding the paha, known as the Iowan Erosion Surface. A well-defined band of pahas runs between Mount Vernon and Martelle, crossed by Iowa Highway 1. Most are in Benton, Linn and Jones counties. Casey's Paha State Preserve in Hickory Hills County Park, Tama County, Iowa preserves the southeast end of a 2-mile long paha. Paha ridges have been identified in Kansas not far from Iowa, in Western Illinois and Eastern Europe. Similar ridge forms occur in the arid upwind parts of the Palouse region of Washington. Outside of the Midwest, several of the above-cited authors use the term greda to refer to features that are indistinguishable from paha ridges
Dinaric Alps
The Dinaric Alps commonly Dinarides, are a mountain range in Southern and Southeastern Europe, separating the continental Balkan Peninsula from the Adriatic Sea. They stretch from Italy in the northwest through Slovenia, Croatia and Herzegovina, Montenegro, Kosovo to Albania in the southeast; the Dinaric Alps extend for 645 kilometres along the Western Balkan Peninsula from the Julian Alps to the northwest in Italy, downwards to the Šar and Korab massif, where their direction changes. The Albanian Alps, or Prokletije, is the highest section of the entire Dinaric Alps. Maja Jezercë is the highest peak and is located in Albania, standing at 2,694 metres above the Adriatic; the Dinaric Alps are one of the most rugged and extensively mountainous areas of Europe, alongside the Caucasus Mountains, Alps and Scandinavian Mountains. They are formed of Mesozoic and Cenozoic sedimentary rocks of dolomite, limestone and conglomerates formed by seas and lakes that once covered the area. During the Alpine earth movements that occurred 50–100 million years ago, immense lateral pressures folded and overthrust the rocks in a great arc around the old rigid block of the northeast.
The Dinaric Alps were thrown up in more or less parallel ranges, stretching like necklaces from the Julian Alps as far as northern Albania and Kosovo, where the mountainous terrain subsides to make way for the waters of the Drin River and the plains of Kosovo. The Dinarides are named after Mount Dinara, a prominent peak in the center of the mountain range on the border with the Dalmatian part of Croatia and Bosnia and Herzegovina; the chain is called Alpet Dinaride or Alpet Dinarike in Albanian, Dinaridi/Динариди in Serbo-Croatian, Dinarsko gorstvo in Slovene and Alpi Dinariche in Italian. The Mesozoic limestone forms a distinctive region of the Balkans, notable for features such as the Karst, which has given its name to all such terrains of limestone eroded by groundwater; the Dinarides are known for being composed of karst — limestone rocks — as is Dinara, the mountain for which they were named. The Quaternary ice ages had little direct geologic influence on the Balkans. No permanent ice caps existed, there is little evidence of extensive glaciation.
Only the highest summits of Durmitor and Prenj have glacial valleys and moraines as low as 600 m. However, in the Prokletije, a range on the northern Albanian border that runs east to west, there is evidence of major glaciation. One geological feature of great importance to the present-day landscape of the Dinarides must be considered in more detail: that of the limestone mountains with their attendant faulting, they are hard and slow to erode, persist as steep jagged escarpments, through which steep-sided gorges and canyons are cleft by the rivers draining the higher slopes. The submerged western Dinaric Alps form the numerous islands and harbors along the Croatian coast; the most extensive example of limestone mountains in Europe are those of the Karst of the Dinaric Alps. Here, all the characteristic features are encountered again and again as one travels through this wild and underpopulated country. Limestone is a porous rock, yet hard and resistant to erosion. Water is the most important corrosive force, dissolving the limestone by chemical action of its natural acidity.
As it percolates down through cracks in the limestone it opens up fissures and channels of considerable depth, so that whole systems of underground drainage develop. During subsequent millennia these work deeper, leaving in their wake enormous waterless caverns and grottoes and forming underground labyrinths of channels and shafts; the roofs of some of these caverns may fall in, to produce great perpendicular-sided gorges, exposing the water to the surface once more. The Dinaric rivers carved many canyons characteristic for Dinaric Alps, in particular karst. Among largest and most well known are the Neretva, the Rakitnica, the Prača, the Drina, the Sutjeska, the Vrbas, the Piva, the Tara, the Komarnica, the Morača, the Cem/Ciijevna, the Lim, the Drin. Only along the Dinaric gorges is communication possible across the Karst, roads and railways tunnel through precipitous cliffs and traverse narrow ledges above roaring torrents. A number of springs and rivers rise in the Dinaric range, including Jadro Spring noted for having been the source of water for Diocletian's Palace at Split.
At the same time, the purity of these rocks is such that the rivers are crystal clear, there is little soil-making residue. Water quality testing of the Jadro River, for example, indicates the low pollutant levels present. Rock faces are bare of vegetation and glaring white, but what little soil there is may collect in the hollows and support lush lime-tolerant vegetation, or yield narrow strips of cultivation. Ruins of fortresses dot the mountainous landscape, evidence of centuries of war and the refuge the Dinaric Alps have provided to various armed forces. During the Roman period, the Dinarides provided shelter to the Illyrians resisting Roman conquest of the Balkans, which began with the conquest of the eastern Adriatic coast in the 3rd century BC. Rome conquered the whole of Illyria in 168 BC, but these mountains sheltered Illyrian resistance forces for many years until the area's complete subjugation by 14 AD. More the Ottoman Empire failed to subjugate the mountainous areas
