Krafla has erupted 29 times in recorded history, most recently in 1984.
Nobody knows when the undersea volcano might next erupt, but Höskuldsson thinks it is only a matter of time.
Still, the people of Iceland are in no danger, he said, because the volcano is so deep under water.
"We wouldn't expect much to happen on the surface."
Mostly, the find indicates how little is known about the seafloor, Höskuldsson said.
"We are getting better techniques, but the oceans of the world are huge."
In the United States, for example, ocean scientists studying a swarm of earthquakes off the Oregon coast are having a hard time pinning down the temblors' source, because much of the seabed is poorly mapped.
"There are all kinds of things on the seafloor we don't know about," said Robert Embley, a National Oceanic and Atmospheric Administration scientist involved in the Oregon project.
Embley, who was not part of Höskuldsson's team, noted that satellite maps of Earth's gravitational field can be used to map out undersea structures.
But these maps don't provide the type of detail found by Höskuldsson. "Even though you can see big features, you can't really tell what they are. All you can say is its a big feature," Embley said.
Höskuldsson will present his results this summer at the annual conference of the International Association of Volcanologists, to be held in Iceland.
Next year, he told the Icelandic press, his team plans to dive to the mountain with a small submarine to gather more clues as to why such a large volcano exists along the ridge.
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