how was devils postpile formed


The range began tilting westward, uplifting peaks along the eastern edge to elevations comparable with those seen today. The lava that n… One such terrane, the Smartville complex, contained the gold veins that would bring wealth and people to the state, some 160 million years later. Because of these traits, basaltic lava tends to have a lower viscosity and will flow more quickly than other lava types. Some breached the surface creating volcanoes and fissures, spewing lava of varying types onto land. A north-south subduction zone was born, and for millions of years oceanic crust continued to slam into the westward moving North American continent. As the mountains rose and great pressures metamorphosed California’s rocks, the subducted crust melted below due to pressure and contact with the Earth’s molten mantle layer. The columns of the Devils Postpile formation .

Current studies suggest that the Postpile was formed less than 100,000 years ago when a cooling lava flow cracked into multi-sided columns. The subducted crust slowly melted from hard rock into magma. This super-continent was the land mass from which all of today’s continents were born.About 200 million years ago, Pangaea began to split and North America began moving to the West while Europe and Asia moved to the East. The lava began filling the valley behind this dam, creating a lava lake 400 ft. deep in some areas. Eventually, a glacier later came over this hidden rock formation, polishing the top of the Postpile and exposing one side of it. The Devils Postpile used to be much taller than what we see today. Devils Postpile National Monument was established in 1911 to preserve these volcanic remains, as well as 101-foot-high Rainbow Falls. Both of these examples have been highly metamorphosed during the millions of years since their original creation. Though the ancestral Sierra Nevada was rising, it was not nearly as high as the mountains we see today. Basalt columns are a common volcanic feature, and they occur on many scales (faster cooling produces smaller columns). Contraction stresses developed because the cool solid form of basalt has a lesser volume than the hot liquid form. The natural landmark is typically open from mid-June through mid-October (weather permitting) and attracts view-seekers, hikers, fisherman and wildlife-watchers. Together they look like tall posts stacked in a pile, hence the feature's name. These cracks expanded to form long post-line columns. In some cases, the magma rose upwards into the continental crust forming large underground magma chambers. Cracks, also called joints by geologists, began to form.

Jointing releases internal stress created by the cooling and associated contraction. Encompassing the Devils Postpile formation, Rainbow Falls and acres of stunning mountain scenery, Devils Postpile National Monument is a Mammoth Lakes must-see. NPS photo. Jointing would have begun at the top, bottom and all around the edges of the lava lake where the lava made direct contact with a cooler surface. The climate became cooler and wetter during these times and as the Sierra Nevada rose higher and higher into the colder elevations, precipitation fell as snow instead of rain. During the intermittent ice ages, so much snow would accumulate that large glaciers formed. Intermittently, North America would get a big chunk of land added to its western margin as volcanic islands, similar to those of Hawaii or Indonesia, were scraped onto the coast, a process called accretion. In this fashion the western edge of North America expanded further and further to the west, and the land we know to be California arrived, piece by piece, like waves from the sea.About 140 million years ago, the friction and pressure between the two plates was so great that the land began to crumple and mountains began to rise east of the subduction zone, the ancestral Sierra Nevada was born. Hornfels near the Minaret Summit and San Joaquin Ridge are likely from this time period as well. For instance, the dark green rocks of the Minarets and the Ritter Range were created by a caldera that formed during this time. The park's main feature, the columnar basalt columns, were formed from a plug of cooling lava nearly 100,000 years ago. The cracks would have extended inwards over time as the more insulated locations within the lava lake finally released enough thermal energy to change from a liquid to a solid state. Several distinct glacial periods have occurred since the Postpile was formed and each has dug deeper and deeper into the dense, heavy rock known officially as basaltic Such depth is uncommon among lava flows and plays a crucial role in the formation of the long columns we see today. The river slowly eats away at pieces that fall into the water. Beginning high up in the Ritter Range, glaciers flowed down the Reds Meadow Valley repeatedly throughout these centuries, shaping the valley to near its present form. Most of the crust slid beneath North America, but occasionally a slice of this sedimentary crust would be thrust onto the continent’s edge. Earthquakes knock columns down into the talus slope below. Some 100,000 years ago, basalt lava flowed from a volcanic vent in the valley of the Middle Fork of the San Joaquin River, filling the valley near the postpile to … Until relatively recently, it was thought to have formed about one million years ago. These rocks can be seen from the bridge near Devils Postpile, a ¼ mile walk from the Ranger Station.By about 2 million years ago, the Sierra Nevada began rising quite rapidly.

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