For the Geo Quiz we are looking for the world's third largest island that is shared by three countries. Most of this island is in Indonesian territory.
The answer is Borneo, which is divided into Indonesia, Brunei and Malaysia.
The Batang Lupar river in Malaysian Borneo is known for its tidal bores. The tidal bore is a force of nature like no other. One of around sixty known to occur in rivers worldwide, the tidal bore in the Batang Lupar River in Sarawak, Malaysian Borneo, is one of the largest. Maria Bakkalapulo jumped onboard a small boat and braved the tidal bore. She sent this report.
A tidal bore requires a precise mix of topography, geography and tides. Simply put, it's when tidewater — funneled into a river's mouth — crashes against the river's outflow. That can cause one huge wave, or set of waves, to travel back upstream — sometimes as much as 50 miles. The height of the waves vary, but the really good ones for surfers are about 10 feet high.
Four French surfers were there to ride the wave — even after spotting three Salt Water crocodiles earlier that day. Bruno Andre is one of them.
"It is exciting because the phenomenon is amazing," Andre said. "The water goes out of the river and when it comes back it makes a huge mass of water coming through and breaking and making a long, long wave. You can surf for many, many miles."
The surfers use fast boats to chase and overtake the waves, jumping on and off, sometimes surfing continuously for five to ten minutes at a time.
Alex Wong is a world champion jet skier. He said it's an amazing ride.
"When I was waiting for the wave to appear, it was just a little white line in the distance. But once it started to roll in, it rolls in on very shallow water, it is more like froth coming at you," Wong said.
He said it is all bubbly, but when it enters the river mouth, it starts to build and it starts to get smooth.
"It is just beautiful, I think that is the right word," he said.
Antony Colas is author of The World Stormrider Guide. He has surfed six of the largest tidal bores in the world.
Colas said that looking at the head of the bore before actually launching into it is very important.
"That is the game. It is like you are catching a train that is moving," he said.
He said the tide never waits or stops for anyone and that riding the actual wave is a feeling of flying.
There's a festive atmosphere whenever there's a tidal bore — or Benak as it's called on the Batang Lupar River. The locals appreciate the tourists, but also find the Benak beneficial in other ways.
Deckson Bundak knows the river well.
"During the Benak time, it is time for us to catch shrimp or fish, for us, for food, for our meals," Bundak said.
He said that when the Benak come they go to the river bank just between the river and the bank and put their fish baskets. The water current pushes the shrimp and fish inside the baskets.
But the easy fishing is not without its dangers. Saltwater crocodiles are common and reach frightening proportions. They kill about half-a-dozen people each year in the area. But despite the risks, the Batang Lupar Benak is becoming more and more popular.