What if there were no earthquakes? by: Mohi Kumar

This might sound like a good thing, after all earthquakes kill thousands of people a year. Just a few weeks ago, more than 1000 people were killed after a magnitude 7.6 earthquake rocked Sumatra near Padang, Indonesia.

But, if there were no earthquakes, there would also be no movements of Earth's crust known as plate tectonics .

Tectonic plates, formed of the Earth's crust and uppermost mantle, cover the surface of the Earth like interlocking puzzle pieces. These pieces are in motion--they collide, separate, break apart, and slide against each other, creating mountains, volcanoes, rift valleys, and deep seafloor trenches. But what if plate tectonics were to stop?

• Colliding plates would cease to uplift mountains. Without any force building mountains, erosion from storms would eventually wear down physical features. This lack of elevation would also alter the flow of rivers, which would turn sluggish. Without the scouring force of steeply falling rivers, erosion would also decrease, leaving behind gently rounded terrain.
• Weather patterns would dramatically change. High mountains trap clouds and create weather patterns--without high mountains, some patterns, like the monsoons, would cease. Tectonics also influences the shape of structures on the ocean floor. These structures influence the flow of ocean currents--without tectonics uplifting continents and channeling currents, the pattern of oceanic circulation might change. Because wind circulation and ocean circulation are strongly coupled, weather and climate would dramatically change in favor of less extremes without tectonics.
• The transfer of heat through the Earth's mantle would likely change. Plate tectonics is thought to be the surface manifestation of a convecting mantle--hot material at the core mantle boundary rises at mid-ocean ridges, cools to form the oceanic crust, and sinks under the more buoyant continental crust through a process called subduction. Thus, stopping the release of heat from the mantle through stopping plate tectonics might mean that more mantle plumes (e.g., hotspots like Hawaii) would spring up as the Earth seeks to cool off.
• Nonetheless, the global climate would likely cool dramatically. Plate tectonics plays a key role in the global cycling of carbon dioxide, an important greenhouse gas that regulates temperature. When mountains erode into sediments, carbon dioxide is pulled from the atmosphere to form soils and limestones. These are transported by rivers to the ocean floor, where they are subducted under the continents. Sinking with the ocean floor are the carbon-rich sediments derived from eroded mountains, along with microscopic skeletons of ocean creatures and water. However, without plate tectonics, the erosion of mountains into sediments would continue to pull out carbon dioxide from the atmosphere, but only volcanoes fed by mantle plumes (e.g. hotspots like Hawaii) would emit carbon dioxide. Even though the number of hotspots might increase and despite fact that the forces driving erosion would diminish without tectonics, more carbon would be trapped than would be emitted, causing climate to cool.
• If the climate cools, biological diversity would likely reduce. Cooler climates would put stress on tropical ecosystems, and wildlife may die out as a result of ecosystem loss.

So a world without earthquakes would be a strange and alien place--earthquakes are central to landscapes, weather, climate, and even life on our planet. Imagine that!

Thanks to Dr. Kelin Whipple, a professor at Arizona State University's School of Earth & Space Exploration, and Lee Kump, a professor at Penn State's Department of Geosciences, for their help in this thought experiment.