MISMEASURE OF A MOUNTAIN

Earthquakes in the Aravallis provide a cautionary tale

- PRANAY LAL

ABOUT 200 kilometres south of Delhi lies Bayana, a largely forgotten town in Rajasthan. Once famed for producing perhaps the world’s first and finest clear crystalline sugar, Bayana rivalled Agra and Delhi in wealth and grandeur. Its sugar owed its reputation to the town’s wells and their water. Then Bayana’s prestige waned. And eventually vanished altogether.

Environmental historians trace the town’s decline to a distant earthquake in 1505 and a gradual depletion of water. Bayana sits in the Bayana Basin, in the eastern part of the North Delhi Fold Belt, within an ancient chunk of the earth's crust known as the Aravalli Craton. The town rests atop undeformed sedimentary rocks formed from river-borne sand deposited in a shallow sea over millions of years. Over time, under high pressure and aided by pulses of immense heat from below, these sediments hardened into rocks between one to two billion years ago. What set in Bayana’s decline is perhaps one, or even two, earthquakes. Neither occurred beneath the town. The first one most likely struck Afghanistan. The Baburnama, the memoirs of the first Mughal emperor, records an earthquake that ruptured the ground at Paghman and Bektut, west of Kabul. It caused the river Kabul to swerve tens of metres away from its old course. Another earthquake, possibly a discrete one, occurred in Kumaon and the western Himalaya of Nepal. Paghman lies nearly 2,000 km away to the northwest and Kumaon-West Nepal's epicentre is at least 400 km north of Bayana, as the crow flies. Perched atop heat- and pressure-tempered sandstone-and-quartzite shoulders of the Aravallis, Bayana perished not because a quake struck below it, but because one struck far away.