Hike Cerro la Jara Trail, Valles Caldera National Preserve, New Mexico

Add to My List Check Off

You are walking in a volcanic caldera – a depression formed during a volcanic eruption. This caldera was formed as the result of a very large volcanic eruption about 1.2 million years ago. It is somewhat circular in shape and 12 to 15 miles across. Alluvial fans get their name from their shape and what they are made of. Rocks, sand, and silt moved and deposited by running water is called alluvium. Alluvial fans are fan shaped deposits of alluvium. Water flowing downhill out of the mountains moves the sediment downhill and deposits it in the valley. Volcanic domes are formed by the extrusion of lava that piles up in a dome shape. Cerro la Jara and South Mountain were formed about 700,000 years after the eruption that formed Valles Caldera. They are both made of a rock called rhyolite. A resurgent dome is different than a volcanic dome; it wasn’t extruded as lava. The resurgent dome was created as magma pushed part of the newly formed valley up from underneath. To understand this better, think of how the upper crust of an apple pie is lifted by the bubbling apples underneath it – the magma pushed the valley floor up, like the hot apples push up the upper pie crust. The volcanic dome, Cerro La Jara is still to your right. This is a good place to see flow banding in the rocks. The banding looks like layers in the rock and indicates that either different lava flows or different lava composition, or both, made the rocks break down and weather differently. Cerro del Medio is a volcanic dome that was formed a few tens of thousands of years after the caldera collapse, when a large lake partly filled Valle Grande. It was the first volcanic dome to erupt after formation of the caldera. The lava that formed the volcanic dome was very hot and contained a lot of silica. It cooled quickly, possibly because it was erupted underwater, and formed rocks called rhyolite and obsidian. So, will the volcano erupt again? When might it erupt? Good questions – what we do know is that there would be plenty of warning signs first. There would be lots of small earthquakes, and the ground temperature and the temperature of water in the springs would increase. This trail is about 1.5 miles (2.4 km) long and will likely take 1 to 2 hours to complete.

Write a Review

No Ratings Yet

Flag as inappropriate ›