The 1797 Riobamba earthquake occurred at 12:30 UTC on 4 February. It devastated the city of Riobamba and many other cities in the Interandean valley, causing between 6,000–40,000 casualties. It is estimated that seismic intensities in the epicentral area reached at least XI (Extreme) on the Mercalli intensity scale, and that the earthquake had a magnitude of 7.6–8.3, the most powerful historical event known in Ecuador. The earthquake was studied by Prussian geographer Alexander von Humboldt, when he visited the area in 1801–1802.