The 1797 Riobamba earthquake, which occurs at 12:30 UTC on February 4, devastates the city of Riobamba and many other cities in the Interandean valley, causing up to forty thousand casualties.

It is estimated that seismic intensities in the epicentral area reach at least XI (Extreme) on the Mercalli intensity scale, and that the earthquake has a magnitude of 8.3, the most powerful historical event known in Ecuador.
The area of significant damage (Intensity ≥VII) extends from Quito in the north to more than sixty kilometers south of Riobamba, including the cities of Guaranda, Ambato, Latacunga and the towns of Saquisilí and Baños.

Riobamba and the town of Quero are both destroyed by landslides.

At the foot of the Tungurahua volcano, the Pastaza River will be dammed by landslides for up to eighty days.

The earthquake will be studied by Alexander von Humboldt, when he visits the area in 1801/2.

Humboldt's analysis of this earthquake will reliy on anecdotal accounts that he gathers during his visit.

Some of the observations such as "the bodies of many of the inhabitants were found to have been hurled to Cullca, a hill several hundred feet in height and on the opposite side of the river Lican", are not credible.

He will a figure of thirty to forty thousand for the number of casualties, while some more recent estimates give figures as low as six thousand.