Des Experts Ont Expliqué Comment Un Fleuve A Abandonné Son Propre Pont

Sympa

Les experts ont expliqué comment une rivière a laissé derrière elle son propre pont, et l'histoire est plus incroyable que vous ne le pensez. Au fil du temps, de puissants courants d'eau ont lentement changé de direction, creusant un nouveau chemin et laissant l'ancien lit de la rivière — et son pont — à sec. Ce qui était autrefois un passage vital au-dessus des eaux tumultueuses est désormais échoué sur des terres vides. Les scientifiques disent que cela peut se produire lorsque l'érosion, l'accumulation de sédiments et les changements naturels du paysage forcent une rivière à changer de cours. Dans certains cas, l'activité humaine, comme la construction ou la déforestation, accélère le processus. Ainsi, ce pont abandonné se dresse maintenant comme un étrange rappel que même les rivières ne suivent pas toujours le plan !  Animation créée par Sympa. ---------------------------------------------------------------------------------------- Musique par Epidemic Sound https://www.epidemicsound.com   Pour ne rien perdre de Sympa, abonnez-vous!: https://goo.gl/6E4Xna​ ---------------------------------------------------------------------------------------- Nos réseaux sociaux : Facebook: https://www.facebook.com/sympasympacom/ Instagram: https://www.instagram.com/sympa.officiel/  Stock de fichiers (photos, vidéos et autres): https://www.depositphotos.com https://www.shutterstock.com https://www.eastnews.ru ----------------------------------------------------------------------------------------  Si tu en veux encore plus, fais un tour ici:  http://sympa-sympa.com

Transcript

00:00Imagine that you crossed a bridge by car to visit a friend.

00:04The next day, you get back in your car to go home,

00:07but there is no longer a river under the bridge you crossed the day before.

00:11Believe it or not, that's exactly what happened to the inhabitants of southern Honduras

00:15when Hurricane Mitch, of Category 5, hit the region in October 1998.

00:22The Choluteca Bridge, which the local authorities had rebuilt earlier that year,

00:26found itself dry in a way, because the river had shifted and no longer passed under it.

00:31The structure quickly became famous on the internet under the name of Bridge to Nowhere.

00:36The course of this waterway changed overnight.

00:38In general, it takes a little longer.

00:42A river will stop flowing in a straight line at any change in the landscape around it.

00:47Even such a tiny thing as a mouse can weaken the banks of a river.

00:51Imagine that a family of mice decide to settle somewhere on the riverbank

00:55and dig a comfortable hole.

00:57Over time, the water enters this hole and begins to carry the furniture floor.

01:03After a few centuries, the river will make an end to this place.

01:07And if you are worried about the family of mice, do not worry,

01:11because it will have moved long before the water floods its house.

01:16Things happen even faster for small streams of water,

01:19because their bed is also small.

01:22The current breaks the stones.

01:24The ground absorbs them.

01:26And this is how a riverbed is formed.

01:29It is in the middle of the watercourse that the current is the strongest,

01:32and its power shapes its bed directly.

01:35The water that flows in rivers and rivers is loaded with earth and other particles.

01:40All these materials go from the source to the mouth,

01:42then throw themselves into the oceans.

01:45In some cases, these particles can also accumulate.

01:48And so new beaches,

01:51among which probably your favorite beach,

01:53are born.

01:55On the other side of the watercourse,

01:57the current is much faster and comes to hit the nearby bank.

02:01So, the erosion process starts again.

02:08Fluvial erosion occurs when the water that flows carries the ground.

02:11And I must tell you that things go very fast in this case.

02:15The water is so powerful that it can even dig into the rock and create gorges.

02:20If the banks of a river are made up of furniture materials,

02:23like humus,

02:24i.e. the earth in which flowers grow,

02:27it is easier for the water in motion to erode them.

02:30In the plains, the rivers are often wide and slow,

02:32because the ground around them offers little resistance.

02:35So you don't have to worry about the waves rocking your boat on a plain river.

02:40In the mountains, the watercourses quickly carry everything that is on their way,

02:45thus revealing the rocky substratum.

02:48Mountain watercourses are generally frozen in the stone.

02:51This rock at the bottom does not move an inch.

02:54Erosion is therefore responsible for the modifications of the watercourse,

02:58but there are also mountains and hills.

03:00When a watercourse reaches a mountain or simply a rock,

03:04it has two possibilities,

03:05bypass it or cross it.

03:08In the plains, the rivers have no natural obstacles

03:11and therefore choose a winding path.

03:13All these turns and detours increase the length of the river,

03:16from the source to the mouth.

03:20The powerful Mississippi River in the United States is an example of this.

03:24It presents many turns and curves,

03:26which are called meanders.

03:28Only in the last century and a half

03:30has the Mississippi changed course several times.

03:33The last major case dates back to 1876,

03:37when it left the historic city of Vicksburg dry.

03:40Two years later,

03:41a team of American engineers came to the region

03:44to build the Yasu Derivation Canal,

03:46which took 25 years to complete.

03:48Thanks to him, the boats could sail again to Vicksburg,

03:52which relaunched the city's economy.

03:55What happened in this city in the south of the United States in the 19th century

03:59is a natural consequence of river erosion.

04:02The curves of a watercourse are accentuated over time,

04:05which accelerates the flow.

04:07The erosion is increased

04:09and the meanders slowly approach each other,

04:11until they merge.

04:13When this happens,

04:15the river becomes straight again the next day,

04:17leaving a lake in the shape of an iron horse

04:19at the place where the elbow was.

04:21This new watercourse is called a dead arm.

04:23These stagnant lakes dry up,

04:26because they are no longer fed by a source,

04:28or turn into swamps.

04:30In some cases,

04:32man uses them as wet meadows for agriculture.

04:38Lake Chico in Arkansas

04:39is the largest dead arm in North America,

04:42formed by the Mississippi several centuries ago.

04:46The Mississippi takes its source in a Minnesota lake.

04:49But a river can also be born from the merger of two other watercourses,

04:53or from the simple rise of underground water.

04:56Even the melting of the snow can feed a river,

04:59like the Amazon that draws its water into the Andes.

05:02Determining the source of a watercourse can be difficult,

05:04which is why the debate on whether the Amazon is longer than the Nile is still open.

05:10What scientists know for sure

05:12is that the Amazon carries more water than any other river.

05:16A fifth of all the fresh water that penetrates the oceans of the earth

05:20comes from this river in South America.

05:22When you look at the Amazon River on a map,

05:25you notice that it flows from Peru to Brazil,

05:28that is, from the west to the east.

05:30This direction may seem strange

05:32if we compare it to that of the Mississippi,

05:34which flows south on the map.

05:36It's confusing because you probably know that rivers flow down,

05:41under the effect of gravity,

05:43but the bottom is not necessarily synonymous with the south.

05:45The water that flows tries to find the easiest way,

05:48so there are no rules in terms of cardinal direction.

05:53The Nile is the best example,

05:55since it flows north, into the Mediterranean Sea.

05:59The north of Egypt, where all the pyramids are located,

06:02is on a land lower than Sudan.

06:04This is where the Nile is formed,

06:06at the meeting point of the Blue Nile and the White Nile.

06:10The Nile, in northern Asia,

06:11and the Mackenzie River, in Canada,

06:14both flow north-west,

06:15while the Yellow River, in eastern Asia,

06:18flows in the same direction as the Amazon,

06:20to the east, to the Pacific Ocean.

06:23These great rivers are among the best proofs

06:25that a stream of water does not necessarily have to flow from north to south.

06:29Gravity is the only important factor

06:31that determines the direction of a stream of water,

06:34because running water is always pulled down.

06:37The flow of water is faster on steep slopes.

06:40When there is a sudden break in the flow,

06:43waterfalls form.

06:45The Salto Angel, in Venezuela,

06:47is the highest waterfall on the planet.

06:50The water falls from a height of 800 meters,

06:52so be careful where you put your feet.

06:55In a waterfall, the water that falls

06:57can easily reach the speed of a Thomson gazelle,

07:00but when a river approaches the end of its course,

07:03it slows down considerably.

07:06The stream of water does not have enough energy

07:07to start the neighboring lands.

07:09All the sediments it has collected along the way,

07:11such as the sandstone, slow it down.

07:15Where a river meets the ocean or a lake,

07:18it gets rid of its sediments

07:19and a delta is created,

07:21a rich and fertile land.

07:23The Ganges, in India,

07:25has the largest delta in the world,

07:27several hundred kilometers wide

07:30and visible from space.

07:32The Amazon, on the other hand,

07:33does not have a real delta

07:34because the strong currents of the Atlantic Ocean

07:36carry everything that the torrent brings it.

07:40The deepest part of the bed of a river,

07:42which is in its middle,

07:43is called a chenal.

07:45This is where the current is strongest,

07:47and it is therefore on these channels

07:49that the ships circulate.

07:51When engineers want to enlarge a navigable route,

07:54they just need to dig a deeper chenal.

07:57And there you go,

07:58the big ships can pass.

08:00This is one of the ways

08:01that man modifies watercourses.

08:03We also often reinforce the banks of a river

08:05to prevent erosion,

08:06or we build dams

08:08that stop or divert the flow of water.

08:10The oldest operational dam on the planet

08:13dates back to the time of the Pharaohs of Egypt.

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