Fill This Form to Contact Me
Total Visitors Till Now
Top Posts & Pages
- Pros and Cons of Urbanization
- List of Metropolitan Cities in India
- Natural Resources: Definition and Classification
- Global Warming: Definitions,Causes,Trends, Effects and Climate Change
- The Structure of the Ocean Floor(Ocean Topography)
- Noise Pollution: Sources and Types
- Geography Study Material for UGC-NET & IAS Exams
- Concept of Region in Geography
- Acid Rain : Causes, Effects and Solutions
- India's Green Revolution:Successes, Failures and Second Green Revolution
- Article Submission
- Geography Study Material for UGC-NET & IAS Exams
- Geomorphology Class Black Board
- Hindi Posts
- Human Geography
- My Projects
- Physical Geography
- Regional Studies
- UGC NET Geography Syllabus
- Useful Links
- Water Resources
- About Me and This Site
The road ahead is inherently unknown
Fear is a faulty navigator
An alluvial fan is a triangle-shaped deposit of gravel, sand, and even smaller pieces of sediment, such as silt. This sediment is called alluvium.
Alluvial fans are usually created as flowing water interacts with mountains, hills, or the steep walls of canyons. Streams carrying alluvium can be trickles of rainwater, a fast-moving creek, a powerful river, or even runoff from agriculture or industry. As a stream flows down a hill, it picks up sand and other particles—alluvium.
The rushing water carries alluvium to a flat plain, where the stream leaves its channel to spread out. Alluvium is deposited as the stream fans out, creating the familiar triangle-shaped feature.
The narrow point of the alluvial fan is called its apex, while the wide triangle is the fan’s apron. Alluvial fans can be tiny, with an apron of just a few centimeters spreading out from the trickle of a drainpipe. They can also be enormous. Over time, water flowing down the Koshi River in Nepal, for example, has built up an alluvial fan more than 15,000 square kilometers (almost 5,800 square miles) wide. This “megafan” carries alluvium from the Himalaya Mountains.
Types of Alluvial Fans
A bajada is the convergence, or of many alluvial fans. Bajadas are common in dry climates, such as the canyons of the American Southwest. Bajadas can be narrow, from the flow of two or three streams of water, or they can be wide, where dozens of alluvial fans converge.
Alluvial fans and bajadas are often found in deserts, where flash floods wash alluvium down from nearby hills. They can also be found in wetter climates, where streams are more common.
Alluvial fans are even found underwater. An underwater fan is created as an underwater current deposits alluvium from a submarine hill or glacier.
Formed Without Water
Sometimes, fans are formed without the aid of water. These are called colluvial fans. Colluvial fans are created by mass wasting. Mass Wasting is is the downward movement of rock, soil, or other material. Alluvium is material transported by water, while colluvium is material transported by mass wasting. Landslides are an instance of mass wasting that often create colluvial fans.
A debris cone is a type of alluvial fan with a steep slope, closer to the shape of a half-cone than a flat fan. Debris cones can be created by the slow accumulation of alluvium over many centuries. They can also form as boulders and other large materials gather during landslides, floods, or other instances of mass wasting.
Alluvial fans can be very diverse habitats. Shrubs such as rabbitbrush and greasewood, or even trees such as ash or willow, are common in the area of alluvial fans. These plants have very deep roots, which can access the water that helped create the alluvial fan, but has now sunken far below it.
Creating a settlement on an alluvial fan can be dangerous. Alluvial fans are prone to flooding. Rushing water, mud, and debris can threaten communities many kilometers away from the apex of the alluvial fan.
Alluvial fans exist on other planets. The presence of alluvial fans on Mars gives evidence for the existence of liquid water on the planet billions of years ago.
national Geographic Society Site
This video says about itself:
How a Team of Female Astronomers Revolutionized Our Understanding of Stars
24 February 2016
At the turn of the 19th century, male astronomers mainly studied galaxies, leaving female scientists wide latitude to research and innovate. Indeed they accomplished truly stellar work. Frebel’s book is “Searching for the Oldest Stars: Ancient Relics from the Early Universe“.
From Science News in the USA:
‘The Glass Universe’ celebrates astronomy’s unsung heroines
Women in the 19th century played underappreciated role in mapping and understanding the stars
By Macon Morehouse
8:00am, November 27, 2016
In the early 1880s, Harvard Observatory director Edward Pickering put out a call for volunteers to help observe flickering stars. He welcomed women, in particular — and not just because he couldn’t afford to pay anything.
At the time, women’s colleges were producing graduates with “abundant…
View original post 686 more words
California enjoys a subtropical and middle latitude location. The climate is much influenced by the state’s latitudinal extent which is a prime determinant of temperatures, wind and humidity. Within the state further climatic variation is influenced by controls that reflect the state’s west coast position and its attitudinal variation.
if the altitude of the entire state is could be reduced to the sea level subtropical environment would be more widespread. Because of latitude temperatures tend to decrease northward from Mexico to Oregon and the growing season becomes shorter. Mountain ranges and maritime influences modify such progression.
California lies between two major worldwide atmospheric circulations – the westerlies and the subtropical high. most of the precipitation comes from westerlies that originate in the North Pacific Ocean and move eastward across North America.California lies to the south of the track followed by many storms: hence precipitation tends to decrease southward. In summer, the subtropical high shifts northwards and consequently western depression move eastward across North America to far north of the state. The entire state tends to be dry in summer.
A large number of people come to California in order to enjoy the benefits of the celebrated climate. It comes as a surprise, therefore, to many newcomers to learn that within the State are to be found a variety of climates, ranging from one extreme to the other. Temperatures have been recorded from minus 45° to 134° F. Annual precipitation at one measuring station has exceeded 161 inches, while other points have gone for more than a year with no measurable rain. A Californian, if he is free to select his living site, may choose almost any kind of climate. This variation in climate results from a number of causes.
The climate of California varies from hot desert to subarctic’. The variation mainly depends on latitude, elevation, and proximity to the coast. California’s coastal regions, the Sierra Nevada foothills, and much of the Central Valley have a Mediterranean climate, with warm to hot, dry summers and mild, moderately wet winters. The influence of the ocean generally moderates temperature extremes, creating warmer winters and substantially cooler summers in coastal areas.
The cool California Current enhanced by upwelling of cold sub-surface waters, often creates summer fog near the coast, creating a warm-summer Mediterranean climate (Köppen climate classification Csb). Further inland, the climate becomes more continental, with some areas turning semi-arid(Köppen BSk), with colder winters and markedly hotter summers. Low-lying inland valleys, especially the Central Valley, have a hot-summer Mediterranean climate (Köppen Csa), with subtropical temperatures but a well-defined summer dry season and a foggy, rainy season in winter.
The temperature gradient between immediate coast and low-lying inland valleys in the south is about 7 °F (4 °C) in winter, the coast being warmer, and in summer roughly 25 °F (14 °C), the interior being warmer. For example, the average daily high in San Francisco in July and August is between 62 and 68 °F (17 and 20 °C),and in Walnut Creek, some 20 miles (32 km) inland, the average daily high in July and August is 90 °F (32 °C): a temperature gain of more than one degree (Fahrenheit) per mile. In the south, the figures are approximately 4 °F and 23 °F (2 °C and 13 °C), respectively. At the coast in Santa Monica, the average high in August is 75 °F (24 °C), while in Burbank, approximately 10 miles (16 km) inland, the average high in August is 95 °F (35 °C): a temperature gain of about two degrees Fahrenheit per mile.
During the cooler winter months (October–March), the Coachella Valley regularly has the warmest winter temperatures out of any place west of the Rocky Mountains. East Los Angeles, the Gateway Cities, and parts of the San Gabriel Valley average the warmest winter high temps (72 °F, 22 °C) in all of the western U.S., and Santa Monica averages the warmest winter lows (52 °F, 11 °C) in all of the western U.S. Palm Springs, a city in the Coachella Valley, averages high/low/mean temperatures of 75 °F/50 °F/63 °F, (24 °C/10 °C/17 °C) respectively during the period of cooler weather from November to April.
The extreme southwest, around San Diego, has a subtropical semi-arid or steppe climate (Koppen BSh) as winters are drier there.
The southeastern regions have a hot arid climate (Koppen BWh), similar to that of the Sahara Desert. In the northern portion of the Mojave Desert on the east side of the state is Death Valley, which has recorded temperatures among the highest in the world. It is common in the summer for temperatures in the valley to reach 120 °F (49 °C). The highest reliably recorded temperature in the world,134 °F (56.7 °C), was recorded in Death Valley on July 10, 1913. Temperatures of 130 °F (54°C) or higher have been recorded as recently as 2005. The 24-hour average July temperature in Death Valley is 101.8 °F (38.8 °C) (1981–2010 NCDC Normals).