This history of Iceland will not make for comforting reading for thousands of would-be air travelers stranded across northern Europe and beyond.

The last time Eyjafjallajökull erupted, it continued belching the Earth's unsettled insides for 14 months, from December 1821 to January 1823.

Scientists do not expect Eyjafjallajökull to keep northern Europe's airports closed for 14 months, but they suggest that Eyjafjallajökull's impact on world travel might not end with the end of this current eruption.

IN PICTURES: Iceland volcano

Moreover, Iceland's "Angry Sister" hasn't even awoken yet. The three times in recorded history when Eyjafjallajökull has erupted, its neighbor, the much larger Katla, has followed suit.

Data do not yet suggest that a Katla eruption is imminent. Yet, in some respects, it is the far greater concern, both in Iceland and beyond.

Katla: the sleeping sister

Katla has erupted 16 times since 930, in 1755 exploding so violently that its ash settled on parts of Scotland. In 1918, Katla tore chunks of ice the size of houses from the Myrdalsjökull glacier atop it, sending them careening down its slopes and into the Atlantic on floods of melted glacier water.

While Eyjafjallavökull is virtually anonymous in Icelandic lore, Katla is one of the "Angry Sisters" along its even-more active twin, Hekla.

The 1918 eruption was the last major eruption of Katla – a volcano that has erupted twice a century, on average – which is why scientists have paid particularly close attention to it in recent days.

But while earth beneath Eyjafjallajökull trembled with thousands of small earthquakes in the months before the eruption – signaling that magma was welling up beneath the volcano – scientists have not seen the same activity at Katla yet.

Even as some scientists suggest that the current Eyjnafjallajökull eruption is abating, the past few days have been only a taste of what Icelanders have known for generations: Their island is one of the most restless places on the planet.

In 1973, an eruption near the nation's primary fishing port split the island of Heimaey in two and required its entire population to be evacuated to the Icelandic mainland by fishing boat.

On 1783, one-quarter of Iceland's population was killed when Laki erupted – an eruption so massive that it changed global weather patterns, bringing record snow to New Jersey and drought to Egypt.

And in the 1755 Katla eruption, the volume of floodwaters from the Myrdalsjökull glacier were estimated to be equal to or greater than the discharge of water from the Amazon, Nile, and Mississippi Rivers combined.

Iceland: an Arctic thread of fire

Much like lands atop the Pacific Ring of Fire, Iceland sits atop a seam in earth's crust, straddling two of the planet's tectonic puzzle pieces.

In other such places, such as Chile, one piece of crust is sliding beneath the other, pushing up the Andes mountains. But in Iceland, new earth is being born with every eruption.

Along the tectonic border marked by Iceland's volcanoes, the world is spreading, gradually pushing Iceland's halves – and the plates they sit on – farther apart. The volcanoes are making new crust, their liquid rock cooling into new landscapes, eruption by eruption, foot by foot.

In this way, Eyjafjallajökull is merely part of the ancient tectonic dance of the continents. But some scientists suggest that the changing global climate could make Icelandic eruptions more common.

As Iceland's glaciers thin, their weight upon the island's volcanoes will lighten, making it easier for magma to rise from the earth's depths, they say.