جستجوی مقالات مرتبط با کلیدواژه "لاهار" در نشریات گروه "جغرافیا"

Kandovan village is situated 58 kilometers from the southwest of Tabriz and 20 kilometers southeast of Oskou East Azerbaijan Province, Iran. The village of Candovan is structurally located in the geological zone of Central Iran and within the range of igneous rocks of the Osku. This village is one of the rare examples of rocky architecture. The Kandovan is a historic village of considered as one of the most beautiful landscapes of the country, with dug houses inside the cone-shaped rocks. Sahand Mountain is an important dormant massive, heavily eroded stratovolcano in East Azerbaijan Province, directly south of Tabriz northwestern Iran. These cone shaped structures (Karans) were shaped by ash and debris from a volcano eruption of now-dormant Sahand Mountain. During the activity, volcanic Sahand diagnosed three stages: the first stage of andesitic lava flows Secondly, intermittent release of ignimbrite (containing fragments of pumice, etc.) dacite and dacite lava flows of the third stage.
After the eruption of Sahand these materials were naturally welded and formed the rocks of Kandovan.
In the Kandovan area, there are three lithological facies. These lithological facies include lava flows or volcanic rocks, ignimbrites, and Lahar and epicclastic deposits. The lava flows mostly have porphyritic texture and their chemical composition is more andesitic and dacitic. These volcanic rocks are usually very fine-grained or aphanitic texture. These rocks often contain phenocrysts. The phenocrysts are feldspar and quartz crystals that are larger than the matrix and are identifiable with the unaided eye. The dominant minerals in these rocks are plagioclase, hornblende, biotite, quartz. The minerals that appear in the form of large crystals and porphyry texture are from feldspar minerals. Textural zoning patterns preserved in plagioclase phenocrysts provide useful information about magmatic evolutions.
According to the welding range of ignimbrite can be divided into three classes in the field (partially welded with pumice, partially welded with fiamme and densely welded). The strength of the resulting ignimberite tuff would depend on how hot the tephra was when it was deposited. Very hot tephra can 'weld' together and not crumble easily. Ignimbrite deposits, which are dig up in the Kandovan village houses, have explosive texture. Their composition and mineralogy those are rock fragments, pumice pieces, volcanic glass and fragments of feldspar and quartz minerals. All ignimbrites are rhyolitic-rhyodacitic in composition.
The welding of clast of volcanic pyroclastic Ignimbrite deposits involves of pumice pieces and rock fragments occurred during explosive eruptions in acidic magma occurs under a compactional load at temperatures above the glass transition temperatures. The welding of pyroclastic materials during Sahand explosions causes the formation of porous, light weight deposit those are susceptible to to excavating.
Over the period of thousands of year’s ash and debris from volcano eruption were hardened, shaped and sculptured by natural elements such as wind, rain, snow and so on. Morphologic change in the area produced present landscape occurred in a semi-arid climate mainly during Quaternary.
Consequently this cone-shaped landforms which originated by tuff erosion were excavated by humans and utilized as dwelling and similar to dwellings in the Turkish region of Cappadocia, are locally called “Karans ".
Around the village the thickness of this formation exceeds 100 m and with time due to water erosion the cone shaped cliffs were formed. The maximum height of the Cone-Shaped is about 60 m. Ignimbrites deposits along the Kandovan valley are under the influence of current water irrigation and atmospheric precipitation, and the shape of the conical hill has formed. Lahar deposits have soft texture and very poorly sorted particles from of clay to gravel size. The Lahara, due to its physical nature, which has a very poorly maturity range from clay to gravel size, is not suitable for digging. Therefore, the conical houses in this group of rocks are not created. Lava flow and Lahar deposit are not suitable for diggings up according to their texture. Lava flows cannot be break down due to its high strength and hardness; therefore, cone-shaped houses cannot be created them.
The most important destructive factors on the Kandovan village are the cases of topography, the physical and chemical properties of the rock, the climate conditions, and, consequently, the biological activities. The effect of physical weathering on the destruction of conical houses in the Kandovan village is more effective than chemical weathering. With the absorbed water causes loss and decomposition of the cement connecting the rock and species damage such as crusting, crushing and alteration Minerals also cause the crystallization of salts as well as the cause of the growth of biological pests in different types. The boundaries of the entrance section of the Kandovan village have been more damaged due to the excessive winds and rains of the western-eastern part of the eastern part, due to the presence of higher hills and higher ranges.

Main objective of this research is comparison between pyroclastic of Malar and Raynah valleys in Yakhar basin in south-east of  Damavand volcano. studing of pyroclastic is very important in recognition of Dmavand volcano.this research is based on descriptive – analytical and using Rayneh Topographic map and Geological map of Damavand, G.P.S AND G.I.S Software.A characteristic of the Reyneh deposite is that clasts below 10 cm are mostly light grey and vescular when broken open, while most larger clasts are dark grey to black.Mallar deposite is whiter than Ryneh pumice most of mallar pumices are fall but most of reyenah pumices are flow. .volume of lahar is more in reyenah.