You won’t find this on the front page of the New York Times or anywhere on CNN.com, but if you have your ear to the tracks you might’ve heard rumblings from far off in the North Atlantic Ocean where, near the Canary Islands, there have been an incredible number of earthquakes recorded in the past week — 620 and counting, 400 in just four days! Fortunately the quakes have been minor in magnitude (1.0-3.0) and of such a depth (5-15km) that they are nearly inconsequential. Except that there have been 620 of them since July 17! This is a sure sign that magma is flowing underneath and pushing toward the surface, but since the earthquakes are located so deep a volcanic eruption is not likely.
Not much about volcanoes is heard in the southern North Atlantic, as it seems their northern neighbors in Iceland are taking most of the headlines. Even YourWeatherBlog has devoted quite a bit of our server space to Katla, Hekla, Grímsvötn and of course, the unpronounceable Eyjafjallajökull. While over in the Pacific Ocean, the Pacific Ring of Fire keeps attention focused from Australia to the Aleutians. Yet the Canary Islands, like the Hawaiian Islands, have been formed from numerous past volcanic eruptions. And, like earthquakes in the Pacific region, the swarm of Canary quakes are resulting from two tectonic plates colliding — this time the African plate and the Eurasian plate. In fact, this region is not far from the triple point of the African, the Eurasian and the North American plates.
El Hierro, one of the western and southernmost islands of the Canary chain, last reported an eruption more than 200 years ago. Yet it’s easy to judge the scale of unrest in this area — 500 open volcano cones can be counted on this single island, and there are approximately 300 more cones that have been covered by lava from previous eruptions.
When considering earthquakes and volcanoes, there is one last feature that goes hand-in-hand with the other two: tsunamis. But a tsunami in the North Atlantic? Yes, indeed. Portugal, Ireland and Scotland have all been hit with tsunamis, both major and minor. Ireland, for instance, has been hit by at least three tsunamis in the past 250 years, while experts predict a large tsunami (10-15 feet) is possible from a quake centered along the Mid-Atlantic ridge separating the North American and Eurasian plates. Portugal was slammed with a massive earthquake (9.0 magnitude centered along the ridge between the African and Eurasian plates) in 1755, followed 40 minutes later by a massive tsunami. Up the road a piece, Scotland was host to a massive tsunami in 6100BC resulting from a massive under-ocean landslide. Not only did this landslide trigger a tsunami that is estimated to have a wall of water 70 feet high, archeologists estimate that it put the final nail in the coffin of Doggerland — the land bridge that once connected Great Britain with Norway.
What comes next? The current earthquake swarm, despite the minor-magnitude quakes, is being monitored closely. A BBC Horizon program from almost 11 years ago featured two geologists hypothesizing that during a future eruption, the western flank of the active Canary Islands volcano Cumbre Vieja could slide into the ocean. This could then generate a giant wave which they termed a mega-tsunami almost 3,000 feet high in the region of the islands. The wave would radiate out across the Atlantic and inundate the eastern seaboard of North America including the American, Caribbean and northern coasts of South America some six to eight hours later. They estimate that the tsunami would have waves possibly 160 feet high causing massive devastation along the coastlines. Modelling suggests that the tsunami could inundate land up to 16 miles inland, depending upon topography.
With that in mind, we now return you to Tropical Storm Don.