The strangest thing is happening. We're getting closer and closer to Earth's equator, where the sun is strongest, but the temperature is getting cooler. Indeed, the night air is downright chilly.

At the same time, we've watched the water temperature drop from 85.8°F (29.8°C) to 79°F (26.1°C). What's going on? We're experiencing the effects of the Humboldt Current, which has traveled north from Antarctica up the Chilean coastline. This current is famous because it brings up deep, cold, nutrient-filled waters off the coast of Peru and Ecuador. The current creates ideal conditions for life on the Galápagos Islands and in the ocean around them.

Because we are traveling southwest from Costa Rica the first Galápagos island to appear on the horizon is Genovesa. Tonight we will test out the MR1 side-scan sonar, a car-sized sonar system that will be towed behind the ship like a fish. This is lucky for Karen Harpp, who is doing her research on Genovesa's strange volcanic history.

Unlike multibeam sonar, the MR1 is towed behind the ship on 600-meter long cable attached to a 2,000-pound weight that keeps the MR1 at about 100 meters below the surface. The cable transmits power to the sonar fish and receives the acoustic returns from the bottom. The detailed side-scan sonar maps made using the MR1 will provide us with the details of the seafloor structure around Genovesa.

"What we're doing here is a huge bonus," Karen says. Unlike the Hawaiian Islands, which follow a neat line away from a hot spot, the Galápagos Islands spread out boxlike from a hot spot, just south of the Galápagos Spreading Center, a mid-oceanic ridge defining the boundary between the Nazca and Cocos plate. But Genovesa, Marchena, Pinta, Wolf and Darwin are different from the rest of the Galápagos Islands.

"I want to figure out how these little guys are related to the hot spot or if in fact they are more related to the mid-ocean ridge," Karen says. It might be, she wonders, that both the hot spot and the spreading center are needed for these islands to exist. "They're sitting between two fires," she says. "They don't follow the rules perfectly."

Deeper Discovery

Multibeam Sonar

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