Cerro La Jara Stop 5

Redondo Peak from the Cerro La Jara Trail.

NPS

The large mountain in the distance directly ahead of you is Redondo Peak. The smaller peak just to the right is Redondito. These mountains are part of a resurgent dome in the center of Valles Caldera. 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. In some areas of Redondo Peak, small amounts of magma did break through, but in general the valley floor was lifted to create the topography. Remember that the valley floor was filled with the material the volcano erupted, so Redondo Peak is made of the valley floor material - the Bandelier Tuff. It took about 30,000 years for Redondo Peak to rise, very fast in a geologic time frame.

Remember the circular ring fracture that caused surface rocks to fall into an empty magma chamber, forming the caldera? A small section of the Valles ring fracture zone is right under you here. You can’t actually see it, but geologists and geophysicists discovered that it is there beneath the surface because of small changes in gravity and the way seismic waves travel through the rocks. There is another ring fracture under you as well – the Toledo ring fracture. The Toledo eruption was similar to the Valles eruption except that it occurred earlier – about 1.6 million years ago. We don’t know as much about the Toledo eruption because Toledo geology was partly destroyed by the Valles eruption.

Continue along the path to Stop 6, which is beyond the sign for the Missing Cabin.