The Lake an Earthquake Made: Chandubi and the 1897 Assam Earthquake That Changed Science

About 64 km from Guwahati, at the foot of the Garo Hills, lies a lake that didn’t exist before the evening of 12 June 1897. Visitors to Chandubi come for the boat rides, the winter birds and the Chandubi festival in January. Few of them know that the lake is a scar from one of the most powerful earthquakes ever recorded in India.

That same earthquake also had a place in the history of science. A geologist studying its records found the first clear evidence that an earthquake sends out separate kinds of waves. That discovery later helped scientists show that Earth has a core. Assam’s earthquake contributed to our basic understanding of the planet’s inner structure.

12 June 1897: the day the ground moved

The earthquake struck in the late afternoon, local time, on 12 June 1897. Modern estimates put its magnitude at about 8.2–8.3, among the largest earthquakes known in the Indian subcontinent.

Its effects were enormous:

• Masonry buildings were reduced to ruins over more than 400,000 km².
• It was felt across more than 650,000 km², from Burma to Delhi, and as far away as Ahmedabad and Peshawar.
• About 1,500 people died. Around 600 of them were killed by a landslide at Sohra (Cherrapunjee).
• At Guwahati the Brahmaputra rose by about 7.6 feet. At Goalpara, waves from the river destroyed the market.

The death toll was relatively low for such a powerful earthquake. The region was thinly populated at the time, and the main shock struck in the afternoon, when many people were outdoors rather than inside heavy buildings.

How Chandubi was born

Chandubi Lake lies in southern Kamrup district, inside the Rabha Hasong Autonomous Council area, close to the Meghalaya border. Barduar Reserved Forest lies to its north and Mayang Hill Reserved Forest to the south.

According to local accounts and the reports that followed, the 1897 earthquake made the land here sink. A patch of forest dropped below its surroundings, and water filled the depression. A forest became a lake.

This kind of change is common after very large earthquakes in soft ground. Strong shaking can compact loose sediment, make waterlogged soil behave like a liquid (liquefaction), and shift the ground surface up or down. The earthquake also reshaped other land and rivers across the region.

The lake isn’t completely cut off. It is linked to the Kulsi river by a channel known locally as the lokeiyadar, along which fish move between the lake and the river.

The lake is shrinking

Chandubi is changing again, and faster. Satellite and map records studied by the Assam Remote Sensing Application Centre (ARSAC), and reported by Mongabay India in 2021, show the water area falling sharply:

Year	Water spread
1954	481.19 ha
1967–68	392.61 ha
1997	203.20 ha
2007	186.52 ha

Over the same period the depth reportedly fell from about 8 m to about 3 m. Parts of the former lakebed are now used for grazing.

People interviewed in the report gave several causes:

• Sand mining in the Kulsi river. Heavy mining has deepened the riverbed. The lake’s water now drains out into the river through the connecting channel, instead of the river feeding the lake.
• Sediment. Soil washed in from the surrounding catchment is filling the lake bed, and some underground feeder streams have been blocked.
• Weed and vegetation growth, which makes the lake shallower still.

Fishing communities report smaller catches. Some have turned to sand mining themselves, which makes the problem worse. Residents have called for a dam on the connecting channel. Biologists, including a scientist from the Wildlife Institute of India, warn that cutting the link between river and lake could harm fish migration and the Kulsi’s river dolphins. Some researchers suggest community management of the catchment and sediment traps instead.

Chandubi was created suddenly by an earthquake. It may be lost slowly to human activity.

The geologist who read the earthquake

In 1897, the Geological Survey of India was headed by Richard Dixon Oldham. He led a detailed investigation of the Assam earthquake and published it in 1899 as the Report of the Great Earthquake of 12th June 1897.

The report recorded several things that were surprising for the time.

The ground was thrown upwards. Witnesses described stones and objects being tossed into the air. Oldham concluded that near the centre, the ground’s acceleration exceeded the pull of gravity. Modern research agrees that vertical acceleration near the epicentre probably exceeded 1 g.

A fault broke the surface. Oldham mapped the Chedrang fault, where one side of the ground rose by up to about 35 feet (around 10 m) compared with the other. Later survey work found ground displacements of up to about 12 feet.

Different waves arrived at different times. Earthquake recording stations were few in 1897. Oldham studied records from distant instruments, mainly in Italy. He saw that the waves did not arrive as one continuous shaking. They came in separate groups:

• P waves (primary): compression waves, the fastest, arriving first
• S waves (secondary): shearing waves, slower, arriving next
• Surface waves: slower waves travelling along the outer surface of Earth, often causing the most damage

This was the first clear identification of the separate arrivals of these wave groups. It became a foundation of modern seismology.

From Assam to Earth’s core

Once scientists knew that P and S waves travel at different speeds and along different paths, they could use them to probe the inside of the planet. Oldham did exactly that. In a paper published in 1906, he compared records from many earthquakes. He found that S waves arrived later than expected at stations far from an earthquake, at more than about 120° around the globe. He explained it with a dense core at the centre of Earth that the waves could not pass through in the usual way.

To be accurate, the core discovery itself came from later earthquakes, not from Assam’s data alone. But the identification of P and S waves, the step that made it possible, came out of Oldham’s study of the 1897 Assam earthquake. Every modern image of Earth’s layered interior depends on that step.

The plateau that “popped up”

For a century, one question remained: what fault caused the 1897 earthquake? No known surface fault seemed big enough.

In 2001, geophysicists Roger Bilham and Philip England published an answer in Nature. They reanalysed old survey measurements from before and after the earthquake. Their conclusion was that a hidden, buried fault beneath the northern edge of the Shillong Plateau had slipped by about 16 metres. They named it the Oldham fault, after the geologist.

Their model showed:

• The fault is about 110 km long and dips steeply beneath the plateau.
• It slipped at depths of roughly 9 to 45 km, possibly down to the base of Earth’s crust.
• The northern edge of the Shillong Plateau was pushed upwards by more than 11 m in seconds.

They described the plateau as a “pop-up”: a block of crust squeezed upwards between faults on its north and south sides. The force comes from the Indian plate pressing north against Asia.

What it means for Assam today

The Bilham and England study also warned of what could come next. The Dauki fault, which runs along the southern edge of the Shillong Plateau, is more than 300 km long and has not slipped in recent times. A future earthquake there could reach about magnitude 8 and seriously affect densely populated areas, including parts of Bangladesh. The interval between such giant earthquakes was estimated at more than 3,000 years. That is very long in human terms, but it says nothing about when the next one will happen.

All of Assam lies in Seismic Zone V, the highest earthquake hazard zone in India’s seismic code. The region has also had another great earthquake since 1897: the 1950 Assam–Tibet earthquake. The lessons are practical ones: earthquake-resistant construction, safe school buildings, and teaching people what to do when the ground starts shaking.

Visiting Chandubi

Chandubi is a day trip from Guwahati. Winter brings migratory birds and better weather. The Chandubi festival, held in the first week of January, features traditional dances by local communities and stalls selling local food. When you visit, choose community-run services where available, and respect the lake’s fragile edges. The fishing channel and the river link both need protection.

Conclusion

The 1897 earthquake killed about 1,500 people, raised the Shillong Plateau by more than 11 m, and created Chandubi Lake. Oldham’s study of its records gave the first clear evidence of separate P, S and surface waves, the step that later made it possible to detect Earth’s core. Today, sand mining, sediment and changing water flows are draining the lake. ARSAC data show its water area more than halved between 1954 and 2007.