Broken Top

The cluster of glaciated stratovolcanoes called the Three Sisters extends for 20 km (12 mi) along the crest of the Cascade Range in Oregon, 35 km (20 mi) west of the city of Bend and 100 km (60 mi) east of Eugene.

South, Middle, and North Sister, as well as Broken Top are high, steep-sided peaks that could produce debris avalanches.

Broken Top is a long extinct volcano that was active in the middle Pleistocene between about 300 and 150 ka.

In 2001, scientists discovered a broad area of uplift west of South Sister that had been rising a few cm (inches) per year since the 1990s. Uplift rates have varied, with a new pulse starting in 2020–2021. Geochemistry data indicate that magmatic activity in the region predates the past few decades.