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, also spelled Tere-Khol', is a shallow freshwater lake
situated in the Tere-Khol Basin within the Sengelen Mountains of the
Republic of Tuva, southern Siberia, Russia. It lies approximately 1,300
meters (4,300 feet) above sea level, about 8 kilometers west of the
Kungurtuk settlement and roughly 50 kilometers from the Mongolian
border, at the headwaters of the Greater Yenisei River. The lake spans
an area that has varied over time due to natural fluctuations, but it is
generally shallow, with average depths of 0.5-0.6 meters in many areas,
though deeper in its western sections. It is fed primarily by the
Balyktyg-Khem River and is part of a unique intermountain depression
filled with fluviolacustrine deposits up to 100 meters deep.
The
lake's origins trace back to the late Pleistocene and early Holocene
epochs, around 11,000 to 10,000 years ago, when the transition from the
last Ice Age led to significant geological changes in the region. It
formed naturally through the damming of the conical inner delta of the
Balyktyg-Khem River, creating a basin in what was already a Neogene-era
depression. This process was driven by glacial melt, sediment
accumulation, and tectonic activity in the seismically active
Altai-Sayan region. Comparative analysis of satellite imagery and
topographic maps from the last few decades reveals that the lake's
shoreline has expanded and contracted periodically, influenced by
climatic variations, precipitation, and evaporation rates. These
short-term oscillations—sometimes observable within a human
lifetime—have led to features like floodplains dotted with bushes and
small ponds, indicating recent inundations.
Prehistorically, the
Tere-Khol Basin was part of a broader landscape inhabited by nomadic
tribes and early Siberian peoples. Archaeological evidence from the
surrounding areas suggests human activity dating back to the Paleolithic
era, with hunter-gatherer communities exploiting the region's rivers,
mountains, and wildlife. However, specific prehistoric sites directly
associated with the lake are sparse, as much of the focus has been on
later historical periods. Local Tuvan folklore often portrays the lake
as mystical, with legends claiming it emerged suddenly from underground
springs, transforming dry land into water. Geological studies, including
continuous aquatic soundings conducted in 2007, have debunked ideas of
an artificial origin (such as damming by humans), confirming its natural
formation.
The Uyghur Period and the Construction of Por-Bazhyn
(8th Century AD)
The most prominent chapter in Lake Tere-Khol's
history revolves around the 8th century AD, during the era of the Uyghur
Khaganate (742–848 AD), a tribal confederation that dominated much of
Central Asia. At this time, the lake was significantly smaller than its
current extent; paleogeographical reconstructions from sub-bottom
sediment analysis indicate that open water existed primarily in the
western part of the basin, west of what is now the island hosting the
Por-Bazhyn ruins. This suggests the "island" may have been connected to
the mainland or part of a drier landscape, allowing easier construction
access.
In approximately AD 777, during the reign of Tengri Bögü Khan
(also known as Bögü Khan, the third khagan of the Uyghurs, ruling
759–779 AD), a large rectangular fortress-like structure known as
Por-Bazhyn ("clay house" in the Tuvan language) was erected on what
became a small island (about 6 hectares) in the lake. Radiocarbon
dating, dendrochronology, and analysis of a carbon-14 spike from AD
774–775 confirm the construction date, pinpointing it to the summer of
777, with building likely spanning two summer seasons. The structure,
covering 3.5 hectares, featured 30-foot (9-meter) clay walls, inner
courtyards, a central palace on an elevated platform, and architectural
elements inspired by Tang Dynasty Chinese styles, including lime plaster
with red stripes and tiled roofs. It was built using adobe bricks and
rammed earth, requiring tens of thousands of tons of material, likely
transported from nearby sources.
Bögü Khan had converted to
Manichaeism—a dualistic religion originating in 3rd-century Persia that
emphasized a cosmic struggle between light and darkness—in AD 763,
declaring it the state religion of the khaganate. Recent studies from
2020 by the Lomonosov Moscow State University and the Institute of
Geography of the Russian Academy of Sciences propose that Por-Bazhyn
served as a seasonal Manichaean monastery rather than a palace or
fortress, explaining its remote location and lack of defensive features
like moats or battlements. This aligns with the khagan's religious
reforms amid internal power struggles, including alliances with China
(he married a Chinese princess) and conflicts with local tribes. The
site's layout mirrors that of Karabalgasun, the Uyghur capital in
Mongolia, further linking it to Uyghur royal architecture.
However,
Por-Bazhyn's occupation was brief. By AD 779, an anti-Manichaean coup
overthrew and killed Bögü Khan, reversing his reforms. The site was
abandoned shortly after, possibly destroyed by an earthquake and
subsequent fire, as evidenced by charred remains and structural damage.
Few artifacts have been found, suggesting it was never fully inhabited
or was evacuated quickly. Local legends attribute the lake's expansion
to water bursting from a well inside the fortress, submerging the
structure and creating the current island—though this is metaphorical,
as water levels rose naturally over centuries due to climatic shifts.
Post-Uyghur Era and Medieval to Early Modern Periods
After the
Uyghur Khaganate's decline in the 9th century, the region fell under
various nomadic groups, including the Kyrgyz and later Mongol influences
during the 13th-century Mongol Empire. Lake Tere-Khol likely served as a
seasonal resource for herders and hunters, but no major settlements are
recorded on its shores until modern times. The lake's isolation
preserved Por-Bazhyn's ruins, which gradually eroded into the water as
levels fluctuated. By the medieval period, the site was largely
forgotten, though Tuvan oral traditions kept alive stories of a "sunken
city" or fortress swallowed by the lake.
Modern Discovery,
Exploration, and Research
The lake and its ruins entered written
history in the 18th century through Russian explorers, but systematic
study began in 1891 when ethnographer Dmitry A. Klements visited
Por-Bazhyn under the auspices of the Russian Geographic Society. He
noted similarities to Karabalgasun and dated it to the Uyghur period.
Initial excavations in 1957–1963 by Sevyan I. Vainshtein proposed it as
a defensive fortress built by Khagan Moyanchur (Bayanchur Khan) in AD
750, based on a runic inscription, though this was later revised.
Large-scale investigations resumed in 2007–2008 by the Por-Bajin
Cultural Foundation, involving geophysicists, archaeologists, and
divers. These efforts, including electrical soundings and sediment
coring, clarified the lake's ancient origins and the fortress's monastic
purpose. Today, rising water levels—exacerbated by climate
change—threaten the ruins, which are partially submerging. The site is a
UNESCO-recognized cultural heritage area, attracting researchers and
eco-tourists, though its remoteness limits access. Ongoing studies
explore seismic history, climate impacts, and potential links to broader
Silk Road networks, underscoring Lake Tere-Khol's role as a window into
Siberia's layered past.
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?