Lake Tere-Khol (also spelled Tere-Khol' or Terekhol) is a shallow freshwater lake located in the remote Sengelen Mountains of southern Siberia, within the Republic of Tuva (Tyva), Russia. Situated near the border with Mongolia, it is best known for hosting the enigmatic ruins of Por-Bazhyn (meaning "clay house" in Tuvan), an ancient fortress on a small island in the lake. The lake occupies a tectonic depression in a highland basin, characterized by permafrost landscapes, and has undergone significant environmental changes over the Holocene period. It exemplifies the ultra-continental, subarid conditions of southern Siberia, with a history intertwined with ancient human settlements, particularly the Uyghur Khaganate. The site draws interest for its archaeological mysteries, natural beauty, and cultural heritage, though its inaccessibility limits tourism.
Lake Tere-Khol is positioned at coordinates approximately 50°36'54"N
97°23'05"E, in the Tere-Khol Basin of southeastern Sayan-Tuva Highland,
about 8 km west of the village of Kungurtuk and roughly 50 km from the
Mongolian border. It lies at an elevation of about 1,300 meters (4,265
feet) above sea level, in a mountainous intermountain depression that
forms part of the upper catchment of the Yenisei River. The surrounding
landscape is dominated by permafrost-affected terrains, with rolling
hills, taiga forests, and steppe elements. The lake's basin is a
pull-apart structure from late Neogene tectonic activity, filled with
fluviolacustrine (river-lake) deposits up to 100 meters thick. Streams
such as Bajirgarnak, Ayuil, Muil-Tuk, and Kungur-Tuk feed the lake,
contributing terrigenous sediments estimated at 3.5 km³ from the Ayuil
stream alone. The island hosting Por-Bazhyn, once possibly a peninsula,
is a permafrost plug that rose centuries before human occupation,
altering the lake's configuration.
The area is remote and hard to
access, requiring helicopter or off-road travel from the Tuva capital,
Kyzyl (about 300 km away). This isolation has preserved the site's
natural and archaeological integrity but poses challenges for research
and visitors.
Lake Tere-Khol is elongated from southwest to northeast, with dimensions that reflect its shallow, expansive nature. Bathymetric surveys using continuous aquatic soundings (CAS) have mapped its bottom topography, revealing a highly indented southern shoreline with straits, bays, and islands during historical periods. The lake's water resistivity is 45-50 ohm.m, and its bottom sediments include various lithotypes like sandy loams, clay-bonded sands, and well-sorted sands, classified by electrical resistivity.
Hydrologically, Lake Tere-Khol is a closed-basin lake with
fluctuating water levels influenced by tectonic, climatic, and
sedimentary processes. Its water area has expanded and contracted over
time; during the 8th century AD (when Por-Bazhyn was built), the open
water was limited to the western part, with the fortress on a peninsula
connected by an isthmus to what is now Promezhutochnij Island. Shoreline
movements have been observed in recent decades, driven by permafrost
dynamics and inflow from surrounding streams. The basin's late
Pleistocene-Holocene evolution involves peat overlapping lake loams,
indicating alternating dry-wet and cold-warm epochs over the last 2,800
years.
Ecologically, the lake is in an ultra-continental subarid
permafrost zone, supporting limited biodiversity adapted to shallow,
cold waters. Vegetation records from nearby sites show
Lateglacial-Holocene shifts, with peat bogs and lake sediments
preserving pollen evidence of environmental changes. The area features
steppe and taiga elements, but specific aquatic ecology (e.g., fish
species or water quality) is understudied due to remoteness. Permafrost
thaw, exacerbated by climate change, affects sediment stability and lake
levels.
The Tere-Khol Basin experiences an ultra-continental climate with extreme temperature variations, cold winters, and short summers. Annual precipitation is low (subarid), with harsh Siberian conditions including permafrost that influences hydrology. Multicentennial records indicate climatic oscillations, such as warmer-wetter periods alternating with cooler-drier ones during the Holocene.
Lake Tere-Khol's history spans geological epochs, but human interest
centers on Por-Bazhyn, built around 777 AD by the Uyghur Khaganate under
Tengri Bögü Khan (also Bögü Qaghan). Initially a palace, it may have
been converted to a Manichaean monastery after Bögü's conversion in 763
AD. Abandoned by 780 AD following Bögü's death in an anti-Manichaean
rebellion, the site suffered earthquakes and fires, with seismic events
during construction and later in the Middle Ages causing collapses. The
fortress was rediscovered in the 18th century, with major excavations in
the 2000s revealing no signs of prolonged occupation (e.g., no pottery
or tools). Geophysical studies (2020) confirmed it was on a peninsula
during construction, with the lake expanding later.
The lake itself
evolved from a late Neogene depression, with Holocene dynamics showing
environmental shifts that affected human settlement.
Por-Bazhyn spans 215 m × 162 m, with rammed-earth walls (hangtu technique) up to 11 m high originally, enclosing courtyards, pavilions, and 30 buildings. It features Tang Chinese influences like dougong brackets and dragon-motif tiles, but with Uyghur typology. The layout mimics an "ideal Buddhist monastery" or "ideal town," with axial planning and ceremonial structures. Traces of fire and earthquake damage are evident, and the site yields artifacts like eave tiles but no daily-use items.
Por-Bazhyn holds cultural importance for Uyghurs as a remnant of their khaganate, featured in modern Uyghur media and on Tuva's district flag. It symbolizes ancient Siberian architecture and mysteries, often called "Siberian Atlantis." Tourism is limited by remoteness, but the site attracted high-profile visits, like Russian President Vladimir Putin and Prince Albert II of Monaco in 2007. Eco-tourism and archaeological tours are possible via helicopter, focusing on the fortress's enigmas and the lake's scenic views.
Ongoing research includes 2020 studies solving construction dates and abandonment via radiocarbon and dendrochronology, attributing ruin to earthquakes. Bathymetric surveys (2007) reconstructed palaeogeography, showing lake expansion. No major recent events (as of 2025) are noted, but climate change impacts on permafrost are a concern. Mysteries persist: Why build in such isolation? Was it stormed or naturally destroyed?