Earth Snapshot RSS Feed Twitter

Posts tagged Tidal Bore

Sediments in the Gironde Estuary, France – February 7th, 2012

44.8N 0.5W

February 7th, 2012 Category: Rivers, Sediments

France - January 4th, 2012

The Gironde Estuary, formed by the confluence of the Garonne and Dordogne rivers, is the largest estuary in Europe at almost 50 miles (80 km) long and up to 7 miles (11 km) wide. The estuary’s average discharge rate into the Atlantic is 265,000 gallons (1 million liters) per second.

It has a large tidal range, of up to 16 ft (5 m) during periods of spring tide, and the strong tidal currents in the estuary, as well as numerous sand banks, tend to hamper navigation. One of the Gironde’s most impressive features is its tidal bore—a large, wall-like wave at the leading edge of the incoming tide—known locally as the Mascaret. Occurring with each flood tide at the time of spring tides (that is, twice daily for a few days every two weeks), the bore surges from the Gironde upstream into its narrower tributaries. On the Garonne, the Mascaret sometimes forms a barreling wave, which can reach a height of 5 ft (1.5 m) and tends to break and reform.

Sediments Expelled by the Amazon River, Brazil

1.6N 49.9W

January 4th, 2010 Category: Rivers

Brazil - November 17th, 2009

Brazil - November 17th, 2009

Thick brown sediments flow forth from the mouth of the Amazon River in northern Brazil. The land west of the river belongs to the state of Amapá, while that east of the river is part of the state of Pará. The habitat of both states is mostly tropical rainforest.

The rivermouth itself, usually measured from Cabo do Norte in Amapá to Punto Patijoca in Pará, is some 330 kilometres (210 mi) wide. As one can observe here, the Amazon does not have a protruding delta. This is due to an intense tidal bore that rapidly whisks away the vast volume of sediments carried by the Amazon before a delta can form beyond the shoreline.

Mouth of the Amazon River, Brazil

1.6N 49.9W

October 8th, 2009 Category: Rivers

Brazil - July 28th, 2009

Brazil - July 28th, 2009

The Amazon River of South America is the largest river in the world by volume and has the world’s largest drainage basin. Here, it can be seen flowing through the Brazilian rainforest to its mouth, carrying an immense load of sediments into the ocean.

The Amazon estuary is some 330 kilometres (210 mi) wide. The width of the mouth of the river is usually measured from Cabo do Norte to Punto Patijoca. This means that the Amazon is wider at its mouth than the entire length of the Thames in England.

Following the coast, a little to the north of Cabo do Norte, and for 160 kilometres (99 mi) along its Guiana margin up the Amazon, is a belt of half-submerged islands and shallow sandbanks.

Here the tidal phenomenon called the bore, or pororoca, occurs, where the depths are not over 7 metres (23 ft). The tidal bore starts with a roar, constantly increasing, and advances at the rate of from 15–25 km/h (9–16 mph), with a breaking wall of water from 1.5–4.0-metres (5–13 ft) high.

The bore is the reason the Amazon does not have a protruding delta; the ocean rapidly carries away the vast volume of silt carried by the Amazon, making it impossible for a delta to grow past the shoreline.