First, when:
The formation of tides is mainly influenced by the rotation of the earth and the gravity of the sun and the moon. The greater the gravity, the greater the tide. Therefore, on the first and fifteenth day of each month, the gravity increases, and the tide will also increase. On the eighteenth day of the eighth lunar month, the sun, the moon and the earth are almost in a straight line. At this time, the influence of tidal force reached its peak, and the tide was the largest on this day.
Secondly, geographical location:
The mouth of Qiantang River is shaped like a trumpet, like a bottle with a big belly and a small mouth. When the tide flows into the mouth of Qiantang River, the channel suddenly narrows and the huge waves suddenly narrow, which is bound to form a rough spring tide. When the tide entering the Qiantang estuary wants to go back, it is stopped by the huge sandbar at the estuary, and it can't get in or out. Then the front waves are blocked and the back waves keep up, which produces a spectacular scene of wave after wave.
Finally, talk about the strong wind:
On August 18, a strong wind came, and the strong wind circled the big waves. The big waves are moving forward with the wind, how can they not be rough?
The above three points have created the spectacular tide of Qiantang River, and people have to sigh the magic of nature's creation.
Extended data:
Every year on the 15th day of the eighth lunar month, the tidal bore of Qiantang River is the largest, and the tidal head can reach several meters. On August 18 of the lunar calendar, the water army inspected the Qiantang River and then observed it as a festival. In addition to the tide-watching festival around August 18 of the lunar calendar, there are quite large tides at the beginning and middle of each month in the lunar calendar, which can be used as a "tide-chasing tour". Around the Mid-Autumn Festival, guests from all directions flocked to watch the wonders of Qian Jiangchao with unprecedented pomp.
Or rush to the river bank at the high tide at the beginning of the year, hurting the tide watchers. The literature contains the poem "Poem Collection of Shi Jing Jiangnan Jingtang Qiantang Guankong": "At first, it began to rain, and suddenly I saw the sea and wanted to float the mountain. Ten thousand people retreat like soldiers, and the turbid waves are higher than the reading altar. " Haining Yan Guan Scenic Area, 50 kilometers away from Hangzhou, is the best place to watch the tide.
Watching autumn tide in Qiantang has become a custom as early as the Han, Wei and Six Dynasties, especially in the Tang and Song Dynasties. According to legend, August 18 of the lunar calendar is the birthday of the tide god, so the tide peak is the highest. In the Southern Song Dynasty, the imperial court stipulated that the navy division should be inspected on the Qiantang River on this day. Later, they became accustomed to each other, and August 18 gradually became a tide-watching festival. Pan Lang, a poet in the Northern Song Dynasty, wrote in Jiuquanzi:
Long memories of watching the tide, full of people vying to see the river. I suspect that the sea is empty and drums are beating all around. Xiang Tao, the frolic in the frolic, stands upright and keeps the red flag wet. I don't see the dream a few times, but I am still chilling.
This poem is a true portrayal of the activities of "making waves" and "watching the tide" in those years.
In ancient Hangzhou, the Phoenix Mountain and Jianggan area were the best places to watch the tide. Due to the change of geographical location, Yan Guan in Haining has been the first scenic spot to watch the tide since the Ming Dynasty, so it is also called "Watching the Tide in Haining".
"Qianjiang Tao Qiu" is famous at home and abroad, and it was popular as early as the Tang and Song Dynasties. On the day of tide-watching, especially in the days around August 18 of the lunar calendar, there were cars and people on the road. Overlooking the bell mouth of Qiantang River, the tide forms turbulent waves, just as Malik is rushing. When the sandbar of the riverbed near Ganpu is blocked, the tidal wave rises by three to five meters, and the tidal range is as high as nine to ten meters. There is indeed a trend of "the sky is full of turbid waves and the rivers and mountains are destroyed". Different places can enjoy different tidal scenes: the tower sees the "first-line tide", the babao sees the "confluence tide", and the old salt warehouse can enjoy the "ebb tide".
References:
Baidu encyclopedia-Qiantang chamber