The Chui Valley is located on the northern edge of the Kyrgyz Republic. The Kyrgyz part of the valley covers the relatively extensive left bank of the Chu River from the meridian of the Boom Gorge in the east to the upper and middle reaches of the river (Aspara) Ashmara, a right tributary of the Kuragaty River in the west. The valley stretches in a latitudinal direction from west to east over a distance of 200 km, and 100 km from north to south at its widest point. To the west and northwest, the valley is open and gradually transitions into the vast sandy desert of Moyun-Kum. The lowest elevations (570-590 m) are observed in the north and northwest near the Tashatkyl Reservoir. To the south and southeast, the elevation increases near the village of Dzhiel-Aryk and reaches 1250 m. Thus, there is a general slope of the plain from east to west, which, along with the slope to the north and northwest flow of the Chu River, has determined its shape.
The Chu River divides the valley into two unequal parts, causing the asymmetry of its cross-section, with a wide left bank (up to 100 km) and a narrow right bank (up to 10 km).
The bottom of the Chui Valley is composed of loose sedimentary deposits, predominantly represented by gravel, sometimes with layers of sand and gravel. Closer to the mountains of the Kyrgyz Ridge, in the foothill zone, the surface formations are represented by powerful coarse-grained debris flows from mountain rivers and temporary watercourses.
Orography
To the south, the Chui Valley is framed by the Kyrgyz Ridge (Fig. 1). In the extreme east, its spurs, known as the Kyzyl-Ompol Mountain, reach a height of 3180 m and do not reach the shores of Lake Issyk-Kul. From this spur, the Kyrgyz Ala-Too extends westward to the Kara-Balta Pass in a latitudinal direction. Then, the axial ridge of the ridge in the western part of the Chu River basin sharply changes its direction from latitudinal to meridional and forms an oval-shaped protrusion directed northward. West of the basin of the Zharly-Kaindy River, the axial ridge aligns again, but acquires a sublatitudinal direction and ends near the city of Taraz (Jambyl region).
In a straight line, the total length of the Kyrgyz Ridge within the specified limits is 360 km, and taking into account the main bends, it is 410 km. Rising near the city of Taraz only 50 m above the river Talas and 640 m above sea level at the Tekturmasa Mountains, the Kyrgyz Ridge gradually increases in height to the east. Between the sources of the Chonor and Makmal-Chal rivers, it rises above the snow line, reaching heights of 3750-3850 m. Further, the ridge again decreases to 2700-2800 m. South of the village of Merke, starting from the basin of the river of the same name in the area of the Kok-Kiya Pass, the heights again increase to 4100-4200 m at the junction of the basins of the Zharly-Kaindy, Chon-Kaindy, and Karakol rivers of the Talas region. Further, the ridge again decreases in the middle part of the Kara-Balta River basin to elevations of 3500-3600 m. But at the sources of the Kara-Balta River (from the Tyo-Ashuu Pass), the heights immediately increase, and the ridge again rises above the snow line. At the meridian of Bishkek, the heights reach 4500-4800 m. A similarly high part of the ridge, but slightly lower at 4200-4400 m, extends eastward to the Shamsy Pass. East of this pass, the axial ridge of the ridge reaches 4000-3800 m, steeply descending to the east towards the Kerke Pass and further to the basin of the Tunduk River.
An important feature of the orography of the Kyrgyz Ridge is that its axial ridge is somewhat shifted to the south of the highest peaks, which are located on the lateral spurs that extend northward.
On the northern slope of the Kyrgyz Ridge, numerous lateral spurs of meridional and closely related orientations extend from the axial ridge. These include the Ala-Archinsky, Alamudunsky, Sokuluksky, Issyk-Ata, and other spurs. The highest elevations of the Kyrgyz Ala-Too are associated with the first of these - the western Alamudun Peak (4895 m). At least 10 peaks of this massif have heights of 4700-4800 m. In the Alamudun spur, the Kyrgyzstan massif rises (4840 m). The continuation of the Alamudun spur is the Ken-Tor spur (4200 m), while the Issyk-Ata spur has a height of 4550 m, and others. On the watershed ridge between the basins of the Noryuz and Issyk-Ata rivers is the peak of the Communist Party of Kyrgyzstan (4483 m).
To the west of the axial ridge of the ridge, several fan-shaped diverging mountain spurs extend, forming private watersheds between river basins. The largest of these are the Ak-Suisky with heights of 4454 m, the Kara-Baltinsky, which rises in the middle part to elevations of 4100-4200 m, the hard-to-reach Chon-Kaindy (4410 m), the Zharly-Kaindy (4260 m), the Ashmirinsky with a height of 4243 m, and the Merken (4150 m).
To the east of the axial ridge of the Kyrgyz Ridge, the following lateral spurs diverge: the Kegetin (Keltorsky) with a height of 4244 m, the Shamsy with 4124 m, the Kyzyl-Suy with 3525 m, and in the far eastern part, the Konorchok spur.
In the extreme northeast of the Kyrgyz Ridge, between the rivers Kychyl-Suu and Kok-Zhar, are the Oktorkoy Mountains. The average height ranges from 2600 to 2800 m, while the maximum is 3125 m (the peak of Kara-Maka).
To the northeast of Oktorkoy is the mountain Baybichenin - Soorus, with an average height of 1800 to 2000 m, and a maximum of 2254 m. The slopes are asymmetrically built. The surface of the leveling is well preserved.
Among the passes of the Kyrgyz Ridge, it is worth noting the Tyo-Ashuu Pass (3580 m), through which the Bishkek-Osh highway runs. Here, at an altitude of 3120 m above sea level, a tunnel 2.8 km long was built in 1960. Other passes, from west to east, include: Makbal (2908 m), Merke, Kara-Balta (3658 m), Ak-Suu (3774 m), Sokuluk, Ala-Archa, Alamudun, Issyk-Ata (3964 m), Kegety (3789 m), Shamsy (3611 m), and others.
The slopes of the Kyrgyz Ridge are asymmetrically built. For most of the Kyrgyz Ridge, the width of the northern slope significantly exceeds the width of the southern slope. Thus, at the meridian of Bishkek, the width of the northern slope is at least 25-30 km, while the southern slope is only 5-10 km. This ratio changes to the opposite at the extreme western end of the ridge, where the width of the southern slope slightly exceeds that of the northern.
The entire surface of the northern slope of the Kyrgyz Ridge is cut by transverse, predominantly gorge-like valleys of the rivers Shamsy, Kegety, Issyk-Ata, Ala-Archa, Ak-Suu, Kara-Balta, and others. The depth of their incision reaches 500-700 m. A significant part of the river valleys has a glacial character in their upper reaches, and downstream they change to gorges. In general, all river valleys have a Y-shaped profile in cross-section.
Along the northern slope of the central part of the Kyrgyz Ridge, two chains of foothills extend in places. They represent step-like rising elevations, so-called shelves. These foothills were described by B.A. Fedorovich (1931), and geologically examined by S.S. Shultz (1948) in their eastern part, in the area between the meridians of the villages of Orlovka and Serafimovsk. The northern edge of the principles adjoins the elevated edge of the foothill plain of the Chui Valley, representing the foothill apron. South of the first shelves extends the Baytyk-Toguz-Bulak depression in a latitudinal direction. Its width in the east is 3-4 km, in the west 8-10 km, with an absolute height of 1050-1450 m. Against the general plain background, the relief of the depression is beautifully expressed by ancient cones of the rivers Noryuz, Alamudun, and Ala-Archa. In the east, the relief of the depression is complicated by the Uch-Emchek anticlinal fold.
Beyond the Baytyk-Toguz-Bulak depression begins a sharp rocky rise of the second, higher shelves, reaching an absolute height of 2201 m at the Shakule Mountain.
On the northern slope of the Kyrgyz Ridge, there are also intermountain basins - Dzhilkildek, Dzhil-Argy, Oktorkoy, Borubai, Kokzhar-Suu, Belsaz, Tatyr, Chunkurchak, Ak-Bashat, and others, lying at various absolute heights (1500-2500 m). The largest of them is the Chunkurchak Basin, which stretches between the Alamudun and Ala-Archin valleys. Its length is 26 km, and its area is 87 km². The river of the same name flows along the bottom of the basin - a left tributary of the Alamudun River. 2-3 km southwest of the village of Tatyr is the picturesque Koguchkon-Sugat waterfall.
The Kyndyktas Mountains, framing the Chui depression in the northeast, are elongated from the southeast to the northwest. Their absolute heights in the east are about 3000 m, decreasing in the west to 1000 m, ending with the Kyndyktas ridge as a plateau-like massif (1000-1100 m).
The watershed plateaus of the Kyndyktas ridge are densely dissected by a network of river valleys, resembling deep, winding canyons. On the steep northern slopes of the massif, these canyons reach depths of 150-160 m, and in the Ak-Tash ridge up to 250-300 m. However, the entire hydrological network of the Kyndyktas ridge is represented only by short and low-water rivers fed by fissure springs, often with intermittent flow due to water loss in the loose deposits of the riverbed. All these rivers, directing their flow into the Chui and Kopin depressions (to the north), are lost before reaching both of the mentioned rivers.
Overall, the peripheral position of the Chui Valley in the north of the republic, its semi-closed nature, and the presence of a huge mountain barrier in the form of the Kyrgyz Ala-Too in the south, as well as the significant elevation fluctuations from 570 to 4895 m above sea level, have a significant impact on the formation of its natural features. The landscapes here develop under conditions of a continental climate with frequent invasions of northern and northwestern air masses, facilitated by the valley's great openness to the northwest. Due to the powerful orographic barriers rising in the south and east, tropical continental air rarely enters the Chui Valley. The mountain barriers cause weak air mass exchange, and the peripheral position on the periphery of the mountain systems of the Tien Shan leads to an unstable winter weather regime with frequently recurring thaws. As a result, a vertical landscape zonality has formed here, reflecting northern boreal features and distinguished as a special northern Tien Shan type.