Neenach Volcano is an extinct Miocene volcano in the Coastal Ranges of California. After formation, the volcanic field was split by a fault in the San Andreas Fault Zone, and over the last 23 million years, the two halves of the volcano have moved about 195 miles (314 kilometers) apart.
The correlation of the two portions, now called the Pinnacles and Neenach volcanic formations, is significant; this correlation has become a "classic example" of plate tectonics for the scientific community. Ten rock types with nearly identical field, petrographic, and chemical characteristics are present in each formation in essentially the same stratigraphic order. [1] This provides ample evidence for the correlation and interpreted movement along the San Andreas Fault.
The volcano formed 23 million years ago [2] during tectonic subduction of the oceanic Juan de Fuca Plate beneath the continental North American Plate, a process often associated with volcanic eruptions near the plate boundaries. Subsequent complex geophysical mechanisms caused a segment of the Juan de Fuca Plate to fuse to the eastern edge of the adjoining Pacific Plate, ending subduction and initiating horizontal shear movement between the plates, with the Pacific Plate moving northwesterly and the North American Plate moving in the opposite southeast direction. [3] This transform movement began approximately 20 million years ago and the resultant shear lineation is the San Andreas Fault Zone. [4] The Neenach Volcano was situated directly over the primary San Andreas fault, causing it to be split in two once the transform fault movement began. [5] The average relative motion along the fault is about 1.5 cm per year, equivalent to six inches per decade. Over the course of this movement, the two halves of the volcano drifted about 195 miles (314 kilometers) apart and eroded down into the minor rock formations visible today.
The remnants of the western portion of the volcano lie in Pinnacles National Park ( 36°29′55.44″N121°12′9.02″W / 36.4987333°N 121.2025056°W ). [6] The most prominent outcrops in the park (High Peaks, Balconies, Machete Ridge and other prominent but unnamed megaliths) consist primarily of eroded pyroclastic flows or air falls, including volcanic breccia, rhyolitic lava flows and volcanic tuff. Remnant andesite lava flows or dikes are also present at a few locations in the park, including the Tourist Trap climbing area and along the West Fork Chalone Creek. [7] The park encompasses approximately 42 square miles and the Neenach Volcanics represent about 20 square miles of the total.
The remnants of the eastern portion of the volcano, called the Neenach Formation, lie about 195 miles (314 kilometers) south of the western portion near Neenach, California. ( 34°44′58.30″N118°35′51.62″W / 34.7495278°N 118.5976722°W ). [6] The formation covers about 10 square miles and is notable for the distinct and strongly linear boundary along its southerly side, where the San Andreas Fault split the original volcano. This entire southern boundary is accessible by Pine Canyon Road (Los Angeles County Route N2) between Sandberg and Three Points. Surface rock exposures in the formation appear to consist primarily of dacite and andesite flows, which have weathered into nondescript low hills with few outcrops, unlike the dramatic megaliths in the northern portion. [8] Satellite imagery reveals several areas of exposed rhyolitic tuff and lapilli tuff, a light green pyroclastic rock that also occurs in Pinnacles National Park and was used to construct the visitor center and other structures there. Although the entire formation appears to be on private property, a segment of the Pacific Crest Trail transects the Neenach from southwest to northeast, with trailheads at the intersection of Lancaster Road (County Road 138) and 269th Street West and along Pine Canyon Road about 0.9 mile east of Horse Trail Campground, which is also on the PCT.
Pinnacles National Park is a national park of the United States protecting a mountainous area located east of the Salinas Valley in Central California, about five miles (8 km) east of Soledad and 80 miles (130 km) southeast of San Jose. The park's namesakes are the eroded leftovers of the western half of an extinct volcano that has moved 200 miles (320 km) from its original location on the San Andreas Fault, embedded in a portion of the California Pacific Coast Ranges. Pinnacles is managed by the National Park Service and the majority of the park is protected as wilderness.
The Mono–Inyo Craters are a volcanic chain of craters, domes and lava flows in Mono County, Eastern California. The chain stretches 25 miles (40 km) from the northwest shore of Mono Lake to the south of Mammoth Mountain. The Mono Lake Volcanic Field forms the northernmost part of the chain and consists of two volcanic islands in the lake and one cinder cone volcano on its northwest shore. Most of the Mono Craters, which make up the bulk of the northern part of the Mono–Inyo chain, are phreatic volcanoes that have since been either plugged or over-topped by rhyolite domes and lava flows. The Inyo volcanic chain form much of the southern part of the chain and consist of phreatic explosion pits, and rhyolitic lava flows and domes. The southernmost part of the chain consists of fumaroles and explosion pits on Mammoth Mountain and a set of cinder cones south of the mountain; the latter are called the Red Cones.
Lassen Volcanic National Park is a national park of the United States in northeastern California. The dominant feature of the park is Lassen Peak, the largest plug dome volcano in the world and the southernmost volcano in the Cascade Range. Lassen Volcanic National Park is one of the few areas in the world where all four types of volcanoes can be found: plug dome, shield, cinder cone, and stratovolcano.
The Lassen volcanic area presents a geological record of sedimentation and volcanic activity in and around Lassen Volcanic National Park in Northern California, U.S. The park is located in the southernmost part of the Cascade Mountain Range in the Pacific Northwest region of the United States. Pacific Oceanic tectonic plates have plunged below the North American Plate in this part of North America for hundreds of millions of years. Heat and molten rock from these subducting plates has fed scores of volcanoes in California, Oregon, Washington and British Columbia over at least the past 30 million years, including these in the Lassen volcanic areas.
Yellowstone Caldera, also known as the Yellowstone Plateau Volcanic Field, is a Quaternary caldera complex and volcanic plateau spanning parts of Wyoming, Idaho, and Montana. It is driven by the Yellowstone hotspot and is largely within Yellowstone National Park. The field comprises four overlapping calderas, multiple lava domes, resurgent domes, crater lakes, and numerous bimodal lava flows and tuff layers of basaltic and rhyolitic composition, originally covering about 17,000 km2 (6,600 sq mi).
The North American plate is a tectonic plate containing most of North America, Cuba, the Bahamas, extreme northeastern Asia, and parts of Iceland and the Azores. With an area of 76 million km2 (29 million sq mi), it is the Earth's second largest tectonic plate, behind the Pacific plate.
The Juan de Fuca plate is a small tectonic plate (microplate) generated from the Juan de Fuca Ridge that is subducting beneath the northerly portion of the western side of the North American plate at the Cascadia subduction zone. It is named after the explorer of the same name. One of the smallest of Earth's tectonic plates, the Juan de Fuca plate is a remnant part of the once-vast Farallon plate, which is now largely subducted underneath the North American plate.
The richly textured landscape of the United States is a product of the dueling forces of plate tectonics, weathering and erosion. Over the 4.5 billion-year history of the Earth, tectonic upheavals and colliding plates have raised great mountain ranges while the forces of erosion and weathering worked to tear them down. Even after many millions of years, records of Earth's great upheavals remain imprinted as textural variations and surface patterns that define distinctive landscapes or provinces.
The Los Angeles Basin is a sedimentary basin located in Southern California, in a region known as the Peninsular Ranges. The basin is also connected to an anomalous group of east–west trending chains of mountains collectively known as the Transverse Ranges. The present basin is a coastal lowland area, whose floor is marked by elongate low ridges and groups of hills that is located on the edge of the Pacific plate. The Los Angeles Basin, along with the Santa Barbara Channel, the Ventura Basin, the San Fernando Valley, and the San Gabriel Basin, lies within the greater Southern California region. The majority of the jurisdictional land area of the city of Los Angeles physically lies within this basin.
The Anahim Volcanic Belt (AVB) is a west–east trending chain of volcanoes and related magmatic features in British Columbia, Canada. It extends from Athlone Island on the Central Coast, running eastward through the strongly uplifted and deeply dissected Coast Mountains to near the community of Nazko on the Interior Plateau. The AVB is delineated as three west-to-east segments that differ in age and structure. A wide variety of igneous rocks with differing compositions occur throughout these segments, comprising landforms such as volcanic cones, volcanic plugs, lava domes, shield volcanoes and intrusions.
Goat Rocks is an extinct stratovolcano in the Cascade Range, located between Mount Rainier and Mount Adams in southern Washington, in the United States. Part of the Cascade Volcanoes, it was formed by the subduction of the Juan de Fuca Plate under the western edge of the North American Plate. The volcano was active from 3.2 million years ago until eruptions ceased between 1 and 0.5 million years ago. Throughout its complex eruptive history, volcanism shifted from silicic explosive eruptions to voluminous, mafic activity.
La Garita Caldera is a large caldera and extinct supervolcano in the San Juan volcanic field in the San Juan Mountains around the town of Creede in southwestern Colorado, United States. It is west of La Garita, Colorado. The eruption that created the La Garita Caldera is among the largest known volcanic eruptions in Earth's history, as well as being one of the most powerful known supervolcanic events.
The Northern Cordilleran Volcanic Province (NCVP), formerly known as the Stikine Volcanic Belt, is a geologic province defined by the occurrence of Miocene to Holocene volcanoes in the Pacific Northwest of North America. This belt of volcanoes extends roughly north-northwest from northwestern British Columbia and the Alaska Panhandle through Yukon to the Southeast Fairbanks Census Area of far eastern Alaska, in a corridor hundreds of kilometres wide. It is the most recently defined volcanic province in the Western Cordillera. It has formed due to extensional cracking of the North American continent—similar to other on-land extensional volcanic zones, including the Basin and Range Province and the East African Rift. Although taking its name from the Western Cordillera, this term is a geologic grouping rather than a geographic one. The southmost part of the NCVP has more, and larger, volcanoes than does the rest of the NCVP; further north it is less clearly delineated, describing a large arch that sways westward through central Yukon.
Quetrupillán is a stratovolcano located in Los Ríos Region of Chile. It is situated between Villarrica and Lanín volcanoes, within Villarrica National Park. Geologically, Quetrupillán is located in a tectonic basement block between the main traces of Liquiñe-Ofqui Fault and Reigolil-Pirihueico Fault.
The Anahim hotspot is a hypothesized hotspot in the Central Interior of British Columbia, Canada. It has been proposed as the candidate source for volcanism in the Anahim Volcanic Belt, a 300 kilometres long chain of volcanoes and other magmatic features that have undergone erosion. This chain extends from the community of Bella Bella in the west to near the small city of Quesnel in the east. While most volcanoes are created by geological activity at tectonic plate boundaries, the Anahim hotspot is located hundreds of kilometres away from the nearest plate boundary.
The Canadian Cascade Arc, also called the Canadian Cascades, is the Canadian segment of the North American Cascade Volcanic Arc. Located entirely within the Canadian province of British Columbia, it extends from the Cascade Mountains in the south to the Coast Mountains in the north. Specifically, the southern end of the Canadian Cascades begin at the Canada–United States border. However, the specific boundaries of the northern end are not precisely known and the geology in this part of the volcanic arc is poorly understood. It is widely accepted by geologists that the Canadian Cascade Arc extends through the Pacific Ranges of the Coast Mountains. However, others have expressed concern that the volcanic arc possibly extends further north into the Kitimat Ranges, another subdivision of the Coast Mountains, and even as far north as Haida Gwaii.
The Geologic history of the Chiricahua Mountains concerns the Chiricahua Mountains, an inactive volcanic range located in Coronado National Forest of southeastern Arizona, in the United States. They are part of an "archipelago" of mountain ranges known as the sky islands that connect the Sierra Madre Occidental in Mexico with the Rocky Mountains. The Chiricahua Mountains are home to a number of unusual geologic features associated with the Turkey Creek Caldera, some of which are protected by Chiricahua National Monument. The landscape has been dominantly shaped by faulting due to Basin and Range extension during the Miocene, volcanic activity, and erosion.
La Reforma is a Plio-Pleistocene caldera on the Baja California Peninsula in Mexico. It is part of eleven volcanoes in Baja California, which formed with the Gulf of California during the Miocene, about ten million years ago. Previously, a volcanic arc had existed on the peninsula. The caldera's basement consists of granites and monzonites, formed between the Cretaceous and the Middle Miocene.
Tocomar is a Pleistocene volcano in the Jujuy Province, Argentina. It is part of the Andean Volcanic Belt, more specifically to its sub-belt the Central Volcanic Zone. The Central Volcanic Zone consists of about 44 active volcanoes and large calderas of the Altiplano-Puna volcanic complex. Volcanism there is caused by the subduction of the Nazca Plate beneath the South America Plate in the Peru-Chile Trench. At Tocomar, volcanism is further influenced by a large fault zone, the Calama-Olacapato-El Toro fault, which runs diagonally across the volcanic arc.
South Island, or Hohnel Island, is a fissure-formed volcanic island and the largest one out of 3 other major islands in Lake Turkana, Kenya. This volcano was discovered in 1888 while it was erupting by Count Teleki, a Hungarian explorer who led the first expedition into the region. It is a part of the Lake Turkana National Parks, which is a UNESCO World Heritage Site.