 | This article may be confusing or unclear to readers.(May 2017) |
Ghost forests are areas of dead trees in former forests, typically in coastal regions where rising sea levels or tectonic shifts have altered the height of a land mass. [1] Forests located near the coast or estuaries may also be at risk of dying through saltwater poisoning, if invading seawater reduces the amount of freshwater that deciduous trees receive for sustenance. [2]
When there is a change in sea level, coastal regions may become inundated with sea water. This can alter coastal areas and kill large areas of trees, leaving behind what is called a “ghost forest.” [3] This type of ghost forest may develop in a variety of environments and in many different places. In the southern US, coastal marshes are expanding into dry wooded areas, killing trees and leaving behind areas of dead trees called snags. Regions of the US at or below sea level are more susceptible to tides. Coastal features affected by changing sea levels are indirectly affected by climate change. With global sea-level rise, the coastlines in the southern US are being altered and leaving behind salt marshes filled with dead and dying trees in some areas. [4]
Ghost forests can also result from tectonic activity. In the Pacific Northwest, there is a large, active subduction zone called the Cascadia Subduction Zone. Here, there is a convergent plate boundary where the Gorda plate, the Juan de Fuca plate, and the Explorer plate are being subducted underneath the North American plate. [5] As these plates attempt to slide past one another, they often become stuck. For several hundred years, the plates will be locked in place and the tension builds. As a result of this tension, there is an orogenic uplift. This is where the tension building between two converging plates gets translated into the vertical uplift of the mountains on the coast. Orogenic uplift is usually associated with earthquakes and mountain buildings. [6] But then, every 500+ years, there is a large earthquake in the Cascadia Subduction Zone and all that built-up tension is released. The release of this tension results in what is called subsidence. [7] And with subsidence the once elevated coastline drops down several meters to below sea level. Here, sea level has not changed, but the coastline has been deformed, making it susceptible to tides. Areas of the coastline can be inundated with sea water, creating marshes and leaving behind ghost forests. The Cascadia event was documented by geologist Brian Atwater in his book, The Orphan Tsunami. Gathering evidence from both the trees and the ground, he determined that the earthquake and tsunami had occurred sometime between 1680 and 1720, but he could not pinpoint the exact date. Japanese scientists, who had extensive records of tsunamis dating back to 684 AD, read the report, and told Atwater that they knew the date and even the precise time: January 26, 1700 at 9:00 p.m. Several hours after the earthquake, tsunami waves had crossed the ocean and wiped out a fishing village. The Japanese were baffled because there was no earthquake anywhere near Japan to account for the tsunami. The ghost forest in Washington thus provided the evidence for its origin. [8]
In addition to subsidence, large earthquakes can also cause tsunamis. It is possible to determine that ghost forests in the Pacific Northwest were created by earthquakes and subsidence by looking at the stratigraphic record. Digging down into the earth, adjacent to a ghost forest, different layers of sediment can reveal the stratigraphy in a ghost forest. Layers of material filled with organic material can indicate where the old forest floor was located prior to subsidence. On top of the layer, there will often be a large sandy deposit. This layer represents the tsunami event, where the coast was flooded with sea water that is filled with sandy sediment. Superimposed on top of the tsunami deposit will be a muddy deposit, representative of an area subjected to ocean tides. [7]
The mountain pine beetle, Dendroctonus ponderosae Hopkins, is a significant ecological force at the landscape level. The majority of the life cycle is spent as larvae feeding in the phloem tissue (inner bark) of host pine trees. This feeding activity eventually girdles and kills successfully attacked trees. Mismanaged forests have resulted in increased mountain pine beetle activity. These direct and indirect effects potentially have devastating consequences for whitebark and other high-elevation pines. [9]
Orogeny is a mountain-building process that takes place at a convergent plate margin when plate motion compresses the margin. An orogenic belt or orogen develops as the compressed plate crumples and is uplifted to form one or more mountain ranges. This involves a series of geological processes collectively called orogenesis. These include both structural deformation of existing continental crust and the creation of new continental crust through volcanism. Magma rising in the orogen carries less dense material upwards while leaving more dense material behind, resulting in compositional differentiation of Earth's lithosphere. A synorogenic process or event is one that occurs during an orogeny.
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 1700 Cascadia earthquake occurred along the Cascadia subduction zone on January 26, 1700, with an estimated moment magnitude of 8.7–9.2. The megathrust earthquake involved the Juan de Fuca Plate from mid-Vancouver Island, south along the Pacific Northwest coast as far as northern California. The plate slipped an average of 20 meters (66 ft) along a fault rupture about 1,000 kilometers long.
The Cascadia subduction zone is a 960 km (600 mi) fault at a convergent plate boundary, about 110–160 km (70–100 mi) off the Pacific coast, that stretches from northern Vancouver Island in Canada to Northern California in the United States. It is capable of producing 9.0+ magnitude earthquakes and tsunamis that could reach 30 m (98 ft). The Oregon Department of Emergency Management estimates shaking would last 5–7 minutes along the coast, with strength and intensity decreasing further from the epicenter. It is a very long, sloping subduction zone where the Explorer, Juan de Fuca, and Gorda plates move to the east and slide below the much larger mostly continental North American Plate. The zone varies in width and lies offshore beginning near Cape Mendocino, Northern California, passing through Oregon and Washington, and terminating at about Vancouver Island in British Columbia.
Megathrust earthquakes occur at convergent plate boundaries, where one tectonic plate is forced underneath another. The earthquakes are caused by slip along the thrust fault that forms the contact between the two plates. These interplate earthquakes are the planet's most powerful, with moment magnitudes (Mw) that can exceed 9.0. Since 1900, all earthquakes of magnitude 9.0 or greater have been megathrust earthquakes.
The Burma Plate is a minor tectonic plate or microplate located in Southeast Asia, sometimes considered a part of the larger Eurasian Plate. The Andaman Islands, Nicobar Islands, and northwestern Sumatra are located on the plate. This island arc separates the Andaman Sea from the main Indian Ocean to the west.
In tectonics, vertical displacement refers to the shifting of land in a vertical direction, resulting in uplift and subsidence. The displacement of rock layers can provide information on how and why Earth's lithosphere changes throughout geologic time. There are different mechanisms which lead to vertical displacement such as tectonic activity, and isostatic adjustments. Tectonic activity leads to vertical displacement when crust is rearranged during a seismic event. Isostatic adjustments result in vertical displacement through sinking due to an increased load or isostatic rebound due to load removal.
Tectonic uplift is the geologic uplift of Earth's surface that is attributed to plate tectonics. While isostatic response is important, an increase in the mean elevation of a region can only occur in response to tectonic processes of crustal thickening, changes in the density distribution of the crust and underlying mantle, and flexural support due to the bending of rigid lithosphere.
The islands of Japan are primarily the result of several large ocean movements occurring over hundreds of millions of years from the mid-Silurian to the Pleistocene, as a result of the subduction of the Philippine Sea Plate beneath the continental Amurian Plate and Okinawa Plate to the south, and subduction of the Pacific Plate under the Okhotsk Plate to the north.
An orogenic belt, orogen, or mobile belt, is a zone of Earth's crust affected by orogeny. An orogenic belt develops when a continental plate crumples and is uplifted to form one or more mountain ranges; this involves a series of geological processes collectively called orogenesis.
Humboldt Lagoons State Park is a California State Park on the Redwood Coast, in Humboldt County, California. It is located along U.S. Route 101 between Trinidad and Orick. The park protects three lagoons with estuaries and wetlands.
The Alpide belt or Alpine-Himalayan orogenic belt, or more recently and rarely the Tethyan orogenic belt, is a seismic and orogenic belt that includes an array of mountain ranges extending for more than 15,000 kilometres (9,300 mi) along the southern margin of Eurasia, stretching from Java and Sumatra, through the Indochinese Peninsula, the Himalayas and Transhimalayas, the mountains of Iran, Caucasus, Anatolia, the Mediterranean, and out into the Atlantic.
A submarine, undersea, or underwater earthquake is an earthquake that occurs underwater at the bottom of a body of water, especially an ocean. They are the leading cause of tsunamis. The magnitude can be measured scientifically by the use of the moment magnitude scale and the intensity can be assigned using the Mercalli intensity scale.
The geology of the Pacific Northwest includes the composition, structure, physical properties and the processes that shape the Pacific Northwest region of North America. The region is part of the Ring of Fire: the subduction of the Pacific and Farallon Plates under the North American Plate is responsible for many of the area's scenic features as well as some of its hazards, such as volcanoes, earthquakes, and landslides.
The geology of Chile is a characterized by processes linked to subduction, such as volcanism, earthquakes, and orogeny. The building blocks of Chile's geology were assembled during the Paleozoic Era when Chile was the southwestern margin of the supercontinent Gondwana. In the Jurassic, Gondwana began to split, and the ongoing period of crustal deformation and mountain building known as the Andean orogeny began. In the Late Cenozoic, Chile definitely separated from Antarctica, and the Andes experienced a significant rise accompanied by a cooling climate and the onset of glaciations.
Tolowa Dunes State Park is a 4,000-acre (16 km2) California State Park located in Del Norte County, on the North Coast of California.
The 1992 Cape Mendocino earthquakes occurred along the Lost Coast of Northern California on April 25 and 26. The three largest events were the M7.2 thrust mainshock that struck near the unincorporated community of Petrolia midday on April 25 and two primary strike-slip aftershocks measuring 6.5 and 6.6 that followed early the next morning. The sequence encompassed both interplate and intraplate activity that was associated with the Mendocino Triple Junction, a complex system of three major faults that converge near Cape Mendocino. The total number of aftershocks that followed the events exceeded 2,000.
The Junggar Basin, also known as the Dzungarian Basin or Zungarian Basin, is one of the largest sedimentary basins in Northwest China. It is located in Dzungaria in northern Xinjiang, and enclosed by the Tarbagatai Mountains of Kazakhstan in the northwest, the Altai Mountains of Mongolia in the northeast, and the Heavenly Mountains in the south. The geology of Junggar Basin mainly consists of sedimentary rocks underlain by igneous and metamorphic basement rocks. The basement of the basin was largely formed during the development of the Pangea supercontinent during complex tectonic events from Precambrian to late Paleozoic time. The basin developed as a series of foreland basins – in other words, basins developing immediately in front of growing mountain ranges – from Permian time to the Quaternary period. The basin's preserved sedimentary records show that the climate during the Mesozoic era was marked by a transition from humid to arid conditions as monsoonal climatic effects waned. The Junggar basin is rich in geological resources due to effects of volcanism and sedimentary deposition. According to Guinness World Records it is a land location remotest from open sea with great-circle distance of 2,648 km from the nearest open sea at 46°16′8″N86°40′2″E.
Pachena Bay is located 13 km (8.1 mi) south of Bamfield in Pacific Rim National Park at the southern end of Vancouver Island, British Columbia, Canada. It was the location of a First Nation's village that was destroyed by a tsunami in 1700.