Photo Gallery El Hierro Rumbles

Massive craters on the Canary Islands show evidence of past volcanic eruptions, and another may be on the way. For weeks, the island of El Hierro has experienced thousands of tiny tremors. As the earthquakes intensify, officials worry its volcano could erupt.
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For weeks, the island of El Hierro has experienced thousands of tiny tremors. El Hierro is the youngest of the Canary Islands, having risen out of the ocean about 1 million years ago. The El Golfo Valley, pictured here, was formed when a third of the island fell back into the sea after an earthquake some 10,000 years ago.

Foto: Manuel Meyer/ dpa
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Every dot on this image from Sept. 18 shows the location of a tremor since mid-July of this year. The red dots show the quakes that happened in the two days before the graphic was made, the green dots represent those occurring more than four days prior, and the blue dots for those in the time in between. Most of the tremors occurred near the volcanic island's magma source.

Foto: Instituto Geografico Nacional
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This image of the earth's surface shows the Canary Islands (Islas Canarias) rising off of the sea floor. All of the volcanic islands except for one have been active in the last million years.

Foto: Instituto Geográfico Nacional
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This graph from Sept. 18 shows a steady increase in earthquakes since July 19 on El Hierro. There have been some 8,000 tremors on the island since then, though until recently most were too weak to be felt.

Foto: Instituto Geografico Nacional
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This graph from Sept. 18 shows the number of earthquakes per day. Red indicates those that were stronger than a 2.0 magnitude.

Foto: Instituto Geografico Nacional
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These volcanic rocks on El Hierro show evidence of earlier eruptions on the island.

Foto: JMN/ Cover/Getty Images
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The points on this map show the locations of GPS systems that measure the earth's movements. In the last few weeks, El Hierro's surface has risen by some 3 millimeters -- indicating that magma below is on the move.

Foto: Instituto Geografico Nacional