Continental Rift Valleys. Very few active rift valleys are found on continental lithosphere. The Baikal Rift Valley is formed by a divergent plate boundary, where the Amur plate is slowly tearing itself away from the Eurasian plate, and has been doing so for about 25 million years. The Amur plate is moving eastward at a rate of about 4 to 5 millimeters. The West Antarctic Rift is one of the most difficult rift valleys to study, because it lies beneath the massive Antarctic Ice Sheet , which can be more than 2 kilometers 1.
The Rio Grande Rift separates the Colorado Plateau , which is generally moving in a clockwise direction, from the older part craton of the North American plate. The most well-known rift valley on Earth is probably the so-called " Great Rift Valley System " which stretches from the Middle East in the north to Mozambique in the south. Today, however, the Great Rift Valley exists as a cultural concept, not a scientific one.
The northern part of the system is the Jordan Rift Valley. Millions of years ago, the Arabian Peninsula was connected to Africa. Seafloor spreading caused the Arabian and African plates to rift apart.
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The Indian Ocean flooded the rift valley between the continents, creating the Red Sea. Today, Africa and Asia are connected by the triangle of the Sinai Peninsula. East African Rift. Throughout the East African Rift, the continent of Africa is splitting in two. Two arms of the Afar Triple Junction continue to widen in the process of seafloor spreading—the arm extending into the Red Sea and the arm extending into the Gulf of Aden. As these rifts continue, the narrow valley created by the Gregory Rift the arm of the Afar Triple Junction located above sea level may sink low enough that the Arabian Sea will flood it.
The Western Rift is one of the most biodiverse regions in Africa, featuring a narrow corridor of highland forest s, snow-capped mountains, savanna s, and chains of lake s and wetland s. Rift lake s, formed as freshwater floods rift valleys, often mark rift valley systems.
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More than a billion years ago, for instance, the North American plate began a rifting process. A triple junction formed in the middle of the young continent, and deep rift valley developed. Freshwater drained and collected in this rift valley, creating a lake.
After millions of years, however, the rift failed. Today, the remains of that ancient rift lake, Lake Superior, rest atop one of the oldest and deepest rift valleys in the world. In addition, over the past 25 million years, layers of soft sediment have accumulate d on the lakebed.
The actual floor of the rift valley is more than 5 kilometers 3 miles deep. Lake Baikal also has the largest volume of liquid freshwater in the world—a staggering 23, cubic kilometers 5, cubic miles. Unlike Lake Baikal, however, the Dead Sea is not a true rift lake as it was not formed entirely by the rift beneath it. The so-called Dead Sea Transform is a geologically complex area, where tectonic plates interact in many ways. The most famous rift lakes in the world may be the series of narrow, deep rift valleys in the East African Rift known simply as the Rift Valley lakes. The Rift Valley lakes, stretching from Ethiopia to Malawi, are sites of amazing biodiversity.
Only Lake Baikal is deeper and holds more water. Like many freshwater Rift Valley lakes, Lake Tanganyika is home to hundreds of endemic species of cichlid fish. Rift valleys are typically deep and narrow. Photograph by Emory Kristof, National Geographic. African Great Lakes. Antarctic Ice Sheet. Also called a collision zone. Great Rift Valley system. Horn of Africa. Also called the geosphere. Middle East. Also called an alkaline lake.
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Several different species of mosquito are able to act as vectors for transmission of the RVF virus. The dominant vector species varies between different regions and different species can play different roles in sustaining the transmission of the virus. Among animals, the RVF virus is spread primarily by the bite of infected mosquitoes, mainly the Aedes species, which can acquire the virus from feeding on infected animals. The female mosquito is also capable of transmitting the virus directly to her offspring via eggs leading to new generations of infected mosquitoes hatching from eggs.
However, when analysing RVF major outbreaks, 2 ecologically distinct situations should be considered. At primary foci areas, RVF virus persists through transmission between vectors and hosts and maintains through vertical transmission in Aedes mosquitoes. Irrigation schemes, where populations of mosquitoes are abundant during long periods of the year, are highly favourable places for secondary disease transmission.
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Outbreaks of RVF in animals can be prevented by a sustained programme of animal vaccination. Both modified live attenuated virus and inactivated virus vaccines have been developed for veterinary use. Only 1 dose of the live vaccine is required to provide long-term immunity but this vaccine may result in spontaneous abortion if given to pregnant animals. The inactivated virus vaccine does not have this side effect, but multiple doses are required in order to provide protection which may prove problematic in endemic areas.
Animal immunization must be implemented prior to an outbreak if an epizootic is to be prevented. Once an outbreak has occurred animal vaccination should NOT be implemented because there is a high risk of intensifying the outbreak. During mass animal vaccination campaigns, animal health workers may, inadvertently, transmit the virus through the use of multi-dose vials and the re-use of needles and syringes.
If some of the animals in the herd are already infected and viraemic although not yet displaying obvious signs of illness , the virus will be transmitted among the herd, and the outbreak will be amplified. Restricting or banning the movement of livestock may be effective in slowing the expansion of the virus from infected to uninfected areas. As outbreaks of RVF in animals precede human cases, the establishment of an active animal health surveillance system to detect new cases is essential in providing early warning for veterinary and human public health authorities.
During an outbreak of RVF, close contact with animals, particularly with their body fluids, either directly or via aerosols, has been identified as the most significant risk factor for RVF virus infection. Raising awareness of the risk factors of RVF infection as well as the protective measures individuals can take to prevent mosquito bites is the only way to reduce human infection and deaths. Although no human-to-human transmission of RVF has been demonstrated, there is still a theoretical risk of transmission of the virus from infected patients to healthcare workers through contact with infected blood or tissues.
Healthcare workers caring for patients with suspected or confirmed RVF should implement Standard Precautions when handling specimens from patients. Standard Precautions define the work practices that are required to ensure a basic level of infection control. Standard Precautions are recommended in the care and treatment of all patients regardless of their perceived or confirmed infectious status.
They cover the handling of blood including dried blood , all other body fluids, secretions and excretions excluding sweat , regardless of whether they contain visible blood, and contact with non-intact skin and mucous membranes. As noted above, laboratory workers are also at risk.
Samples taken from suspected human and animal cases of RVF for diagnosis should be handled by trained staff and processed in suitably equipped laboratories. Other ways in which to control the spread of RVF involve control of the vector and protection against their bites. Larviciding measures at mosquito breeding sites are the most effective form of vector control if breeding sites can be clearly identified and are limited in size and extent.
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During periods of flooding, however, the number and extent of breeding sites is usually too high for larviciding measures to be feasible. Forecasting can predict climatic conditions that are frequently associated with an increased risk of outbreaks, and may improve disease control. The response of vegetation to increased levels of rainfall can be easily measured and monitored by Remote Sensing Satellite Imagery. Early warning systems, such as these, could be used to trigger detection of animal cases at an early stage of an outbreak, enabling authorities to implement measures to avert impending epidemics.
Within the framework of the new International Health Regulations , the forecasting and early detection of RVF outbreaks, together with a comprehensive assessment of the risk of diffusion to new areas, are essential to enabling the implementation of effective and timely control measures. The unit was deployed for field investigation on 31 August In Niger, the WHO Country Office provides technical and financial support for surveillance, outbreak investigation, technical guidelines regarding case definition, case management, shipment of samples, and risk communication.
Rift Valley fever 19 February Key facts Rift Valley fever RVF is a viral zoonosis that primarily affects animals but can also infect humans. The majority of human infections result from contact with the blood or organs of infected animals.