NB: now corrected with images of the site.

Over the weekend there has been a number of news stories about a peculiar event in Brazil on Thursday night. This news story from the BBC is typical:

A mining company in Brazil says an inquiry has begun into the cause of the collapse and sinking of a floating port on the Amazon river, in Amapa state.  Rescue operations are under way to locate six workers who went missing.  An official blamed a big wave that allegedly washed over the banks of the Amazon, dragging with it cranes, lorries and people … “There was a wave that washed over the banks of Santana, even reaching the island of Santana. This wave also hit the company’s port,” Paulo Oliveira, a spokesman for Anglo Ferrous told the local channel TV Amapa. Other witnesses, however, told reporters that the quick and powerful water surge was a consequence of the landslide and the sinking of the floating port facilities, which were used for loading ships with iron ore.

In a statement, Anglo-American said the causes of the collapse were being investigated. “An iron ore vessel was docked at the pier for loading at the time and was hit by flood waters. Flood waters also dragged vehicles and shipping equipment into the river,” the company said. Authorities avoided pointing fingers before the experts complete their tasks. “Right now, it would be inappropriate to try and find a culprit, but after a detailed survey, we will get to understand the causes and be able to attribute responsibilities,” the state governor of Amapa, Camilo Capiberibe, said.

The same report also has this image of the site:

http://www.bbc.co.uk/news/world-latin-america-21971513

Other reports suggest that a landslide occurred.  For example, Fox News report:

Details on the exact cause of the accident, which occurred shortly after midnight at the port of Santana and is being investigated, weren’t immediately known. Firefighters from Brazil’s northern Amapa state said a stretch of riverbank roughly 200 meters long collapsed, causing a pier to sink into the water …  “The water is very murky and about 25 meters deep, which is making the search difficult,” a firefighter said. He added that heavy rains in recent days suggest a possible landslide. On the other hand, Anglo-American said in a statement that “initial information attributes the accident to an unusually large mass of water moving along the river, as other ports located in the region were also affected.”  A ship captain present at the port initially described the incident as a tsunami, a theory that was later discarded. One vessel loading iron ore at the pier was damaged, a shipping source said.

http://pedlowski.blogspot.co.uk/

http://www.alcinea.com/geral/anglo-suspende-atividades-em-santana

All of the evidence suggests to me a failure of the land on the river bank, which then generated the wave that was observed by the ship’s captain.  Interesting, if so his observation of a tsunami is correct, albeit a very localised one.  These sort of collapse events can be very dramatic, as an earlier (and rather larger) event on a Brazil dockside (in Manaus in 2010) demonstrated: