Shashan

Shashan "borrows the green leaves from the south of the Yangtze River to decorate the jadeite of the peninsula, and moves to the yellow sand in the north of the Great Wall to achieve the desert scenery." Who can solve the mystery of nature? When you enter the feicui Island Scenic Area, you can see the rolling yellow sand dunes in the distance, which makes you feel like you are in the Gobi desert. The desert of feicui Island stretches from the East, and then turns to the southwest sea at an angle of 30 degrees. Golden sand dunes, soft like silk, round like an egg, curve like a fish ridge, quiet like a virgin.

Shashan

Sand Mountain refers to giant sand dune or sand dune chain with relative height above 100 meters. Hills, sand mounds, sand ridges or other loose materials formed by the action of wind are called sand dunes. The existence of sand dunes is caused by wind moving unconsolidated material. Sand dunes are usually associated with large areas of desert occupied by wind blown sand. In the Sahara desert, for example, sand deposits account for about 7 million square kilometers. The types of sand dunes can be classified according to the structure of sand laden airflow, wind direction and sand content, and also according to the relationship between wind direction and sand dune morphology.

move

There are two ways of sand movement.

First, through the process of jumping, the wind blows the sand up, moves it for a short distance, and then falls. When the sand is scraping over a rocky surface, it may bounce several meters high, otherwise it will move only a few centimeters above the surface.

Second, the jumping sand particles collide with the ground again and push other sand particles forward with the help of impact force. This movement is called surface creep. The simplest way to form a sand dune is: an obstacle, such as stones and plants, blocks the airflow and makes the sand pile up on the windward side. As the sand dunes gradually increase, the blocking effect on the sand carried by the wind is greater, and the jumping sand particles are intercepted in the leeward shelter. After the dune increases, it begins to move slowly along the wind, showing a more asymmetric shape. The disturbance of sand dunes to air flow is more and more serious. At this time, on the windward side of the sand dune, the wind speed increases, and the jumping sand particles are blown upward, and then cross the peak and fall to the upper part of the downwind slope, resulting in a steep sliding surface. The diameter of sand grains in sand dunes is usually less than 1 mm, and the angle of repose at which sand grains can stop is about 35 degrees. When the steeper upper part of the sliding surface reaches or exceeds this angle, the slope becomes unstable. The sand eventually slides down the slide, and the dunes move forward. That's why the dunes move. The view that obstacles lead to the formation of sand dunes cannot explain how sand dunes form on a smooth, horizontal surface and form a sand sea composed of many sand piles of equal size and shape. There is a view that this kind of sand dune is caused by the friction between the air and the ground, and the formation of this kind of sand dune is very similar to that of sand ripple on the riverbed or beach. Crescent dune is a typical desert terrain. The crescent shaped dunes may be connected to the sea of transverse dunes in the area where there is a lot of sand. Parabolic dunes are formed where plants are damaged and blown out of a depression by the wind. Although they are slightly crescent shaped in plan, the tip of the crescent extends upwind and the sliding surface is outside the crescent dune. They move along the wind, forming a U-shape). The height of crescent dunes can exceed 27 meters. Long strip dunes are long ridges. Generally speaking, they form a line along the direction of prevailing wind. The sliding surface of such dunes is likely to be formed by vortices. The sand in the hollow between the ridges of the strip dunes has been blown away by the wind. Sand ridges extend for a long distance, sometimes several kilometers. Sand dunes are mainly crescent shaped and strip shaped. In some places, there is a kind of star or pyramid dune, which is polygonal star on the plan. The dunes are thought to be immobile, so they become landmarks for desert travelers.

type

The types of sand dunes can be classified according to the structure of sand laden airflow, wind direction and sand content, and also according to the relationship between wind direction and sand dune morphology.

There are three main types of sand dunes

① Crescent dunes, also known as transverse dunes. The plane is like a crescent moon, and its strike is perpendicular to or greater than 60 ° to the wind direction. On both sides of the sand dune, there are two sharp angles extending forward along the wind, with a height of several meters to more than ten meters. The windward slope is convex and gentle, with a slope of about 5 ° to 20 ° and the leeward slope is concave and steep, with a slope of about 28 ° to 34 °. The formation process can be divided into three stages: cake shaped sand pile stage, shield shaped sand dune stage, rudimentary crescent shaped sand dune stage and crescent shaped sand dune formation stage. The wind sand flow through the sand pile produces different wind speed changes and different air pressure distribution characteristics. The wind speed at the top of the sand pile is high and the air pressure at the leeward slope is low and the air pressure at the leeward slope is high. The leeward slope of the sand pile forms eddy currents and piles the sand on both sides of the leeward slope, forming a horseshoe shaped small depression between the two sharp corners of the leeward slope. The depression continues to expand and the rudimentary crescent shaped sand dunes form. The sand grains on leeward slope slide down due to gravity, the eddy current blows to both sides and develops two wings. Crescent dunes are connected to form crescent dune chain, compound crescent dune and compound dune chain. When the surface of the horizontal dune is obstructed by the plant shrub, the parabolic dune can be formed, and the plane shape is just opposite to the crescent shape. It continued to develop and form parallel low twin sand ridges.

② Longitudinal sand ridges. The trend of sand dune morphology is basically consistent with the direction of sand wind (generally less than 30 °). It is a long strip, up to tens of kilometers long, about ten meters high and hundreds of meters wide. When the sand source is abundant, a compound longitudinal sand ridge is formed.

③ Under the action of long-term windy sand flow, pyramid dunes and honeycomb dunes can be formed in the Piedmont or in the area with complex terrain.

Address: south coast of gold coast, Changli County, Qinhuangdao City, Hebei Province

Longitude: 119.286804

Latitude: 39.571028

Chinese PinYin : Sha Shan