Qualla: Romeral fault system

Romeral fault system: Introduction

Thu, 23 Apr 2026 00:00:00 GMT

Photo credit Carlos A Arango, Public domain. Run a pen down the map of western Colombia and the cities line up along it like beads on a thread: Sincelejo, Medellín, Manizales, Pereira, Armenia, Cali, Popayán, Pasto. That line is the Romeral fault system - a 200-million-year-old scar where oceanic crust welded onto the ancient western edge of South America. The Cauca River fills the valley the fault carved. The Andes' Western and Central ranges rose on either side of it. And on March 31, 1983, and again on January 25, 1999, the fault briefly remembered it was still alive.

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Image: Carlos A Arango | Public domain

Romeral fault system: An Ancient Suture

Thu, 23 Apr 2026 00:00:00 GMT

Photo credit Grundkarte Milenioscuro, Relief Alexrk2, CC BY-SA 3.0. The Romeral fault system has been moving since the Triassic - more than 200 million years. During the Cretaceous it was the western margin of northwestern South America, the literal edge of the continent before later mountain-building stitched additional crust onto it from the Pa...

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Image: Grundkarte Milenioscuro, Relief Alexrk2 | CC BY-SA 3.0

Romeral fault system: Five Plates Meet Here

Thu, 23 Apr 2026 00:00:00 GMT

Photo credit Carlos A Arango, Public domain. Colombia sits where five tectonic plates crowd one another: the Caribbean, the Panama, the Coiba, and the Malpelo (the last three formerly lumped into the Nazca plate), plus the North Andes plate that carries most of the country. The Romeral fault system tracks the seam where the...

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Image: Carlos A Arango | Public domain

Romeral fault system: Volcanoes Overhead

Thu, 23 Apr 2026 00:00:00 GMT

Photo credit Bernardo Andrade Tapia, CC BY-SA 3.0. The active volcanoes of Colombia trace the fault zone. Galeras, which smokes above Pasto and has killed scientists at its crater, is underlain by the Romeral system. So is the Romeral volcano itself, which gave the system its name. So are the volcanoes of the southwestern chain r...

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Image: Bernardo Andrade Tapia | CC BY-SA 3.0

Romeral fault system: Popayán, 18 Seconds

Thu, 23 Apr 2026 00:00:00 GMT

Photo credit Carlos A Arango, Public domain. On Maundy Thursday morning, March 31, 1983, the Rosas-Julumito fault (or the nearby Julumito Fault, less than 2 kilometers west) slipped for eighteen seconds beneath Popayán. The magnitude was only Mw 5.5 - modest by global standards - but the quake struck a 400-year-old colonial...

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Image: Carlos A Arango | Public domain

Romeral fault system: A System Still Moving

Thu, 23 Apr 2026 00:00:00 GMT

Photo credit Carlos A Arango, Public domain. Individual segments slip at rates from 0.2 to a few millimeters per year. That seems slow - and it is, by human measure. But the fault has been moving for 200 million years, and the slippage accumulates. Strike-slip along Romeral has had at least three phases since the Miocene: r...

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Image: Carlos A Arango | Public domain