La Ventana Arch
What created the natural features at La Ventana Natural Arch?
Rather than being formed from uplifted sandstone as most arches are, the Ventana Arch formed within a magma intrusion called a volcanic dike. Lava from the Summer Coon volcanic complex intruded into cracks in the surrounding alluvial and volcanic deposits about 30 million years ago.
Although the arch area is surrounded by extensive black lava fields, the arch itself is composed of Zuni sandstone. Compressed sand dunes were eventually hardened enough to become a soft rock, easily eroded by wind, water and frost wedging. Deep cracks found in the rock allow water to penetrate. When water expands by freezing temperatures, rock fragments are forced out. Constant freeze and thaw cycles eventually form an opening in the arch face. The talus slope below the arch reminds us that the size of the arch window will continue to grow as it weathers, and some day in the distant future it will return to being sand.
La Ventana Arch
What created the natural features at La Ventana Natural Arch?
Rather than being formed from uplifted sandstone as most arches are, the Ventana Arch formed within a magma intrusion called a volcanic dike. Lava from the Summer Coon volcanic complex intruded into cracks in the surrounding alluvial and volcanic deposits about 30 million years ago.
Although the arch area is surrounded by extensive black lava fields, the arch itself is composed of Zuni sandstone. Compressed sand dunes were eventually hardened enough to become a soft rock, easily eroded by wind, water and frost wedging. Deep cracks found in the rock allow water to penetrate. When water expands by freezing temperatures, rock fragments are forced out. Constant freeze and thaw cycles eventually form an opening in the arch face. The talus slope below the arch reminds us that the size of the arch window will continue to grow as it weathers, and some day in the distant future it will return to being sand.