Nevado del Ruiz is part of the Andean Arc volcanoes on the west coast of South America. The coasts of North and South America form part of the Pacific Ring of Fire which also includes the east coast of Asia and many islands.
Nevado del Ruiz is situated in Los Nevados National Park which is located 80 miles west of Bogota, Colombia. It is one of five volcanoes in the Ruiz-Tolima volcano massif. The other volcanoes are Nevado del Cisne, Quindio, Santa Isabel and Nevado del Tolima. All of these mountains are ice-capped stratovolcanoes and are vulnerable to seismic activity due to lying at the intersection of four fault lines.
Events Leading up to the Eruption of Nevado del Ruiz
The first sign of volcanic activity started in November, 1984. Small earthquakes occurred and fumaroles, which spew gas and steam, were detected at the summit along with small magma eruptions.
This activity continued for ten months and on September 11, 1985, there was a large ejection of ash from the peak of Nevado del Ruiz. This was a signal that an eruption was imminent.
On November 10, 1985, tremors became more constant. This was a sign of magma movement within the mountain.
Eruption of Nevado del Ruiz
- In the mid-afternoon of November 13, 1985, a phreatic eruption occurred. This is where magma makes contact with surface water and creates steam. As a result, there was an explosion of rock, ash and water.
- Six hours later, at approximately 9:00pm, a series of strong earthquakes occurred along with pyroclastic eruptions. These eruptions are swift-moving currents of hot gas and rock which can travel away from the volcano at speeds up to 450 mph. These eruptions continued for over an hour.
- At 10:4pm, a lahar flowed down the northwest side of Nevado del Ruiz and wiped out the village of Chinchina.
- At 11:35pm, the first lahar cascaded down the east side of the mountain at the speed of 24 feet per second and struck the city of Armero.
- At 11:50pm, additional lahars flowed down Nevado del Ruiz and struck Armero again.
In a fact sheet published by the Geology Department at the University of Wisconsin, “One lahar flowed 70 km from volcano, destroying the town of Armero. The lahar had a depth of 40 m, and traveled at 30-40 km/hr. In addition to the more than 22,000 people killed, 10,000 people were left homeless”.
Geologists and scientists were monitoring the volcano and had mapped out the predicted damage from lahars, which are flows of volcanic debris. The map was not finalized in time for the government to issue evacuation orders.
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