Seemorerocks: Methane hydrates and seismic activity

Thursday, 26 September 2013

Methane hydrates and seismic activity

Methane Release caused by Earthquakes

15 September, 2013

Methane hydrates can become destabilized due to changes in temperature or pressure, as a result of earthquakes and shockwaves accompanying them, severe storms, volcanic activity, coastal collapse and landslides. Such events can be both primed and triggered by global warming, as follows:

As more ice melts away on Greenland and more water runs off into the sea, there is less weight on the Earth’s crust under Greenland. The crust and mantle can bounce back during a large melt, an effect that is called 'isostatic rebound'. This rebound can not only trigger earthquakes and landslides, it can also suck up the magma in the Earth’s crust and trigger volcanic eruptions.

The added weight of water from melting glaciers stresses the Earth’s crust underneath the sea, which can cause earthquakes. This is especially the case for coastal waters, where the impact of the water that flows into the sea is huge, not only in terms of weight, but also in terms of the currents they cause.

As the permafrost melts, mountain ranges, soil and submarine sediments all become less robust. Where the permafrost previously held things together, we can now expect more coastal collapse, avalanches and landslides, which can send shockwaves through the sea that in turn trigger earthquakes and hydrate destabilization.

Methane hydrates that are on the edge of stabilization can be disturbed by global warming in two additional ways, temperature and pressure: Warming of the Earth's crust as heat penetrates sediments on the seafloor. Thermal expansion of the Earth's crust means that the crust will expand slightly in volume, resulting in expansion of the cavity that holds the hydrates.

Finally, there's the additional impact of methane itself. Permafrost previously kept methane stable in sediments. Methane converting from hydrates into free gas will expand some 160 times in volume; this explosive process can trigger further destabilization. Once released into the atmosphere, the methane has a huge local warming potential, adding to the threat that further methane releases will occur locally.

Back in 2006, Bill McGuire said: "A particular worry is that this in turn will contribute to large-scale releases of methane gas from the solid gas hydrate deposits that are trapped in marine sediments. Gas hydrates have been identified around the margins of all the ocean basins, and outbursts of gas may occur as sea temperatures climb or as rising sea levels trigger underwater quakes in the vicinity."

For more than a decade, Malcolm Light, contributor to the Arctic-news blog, has been warning about the danger of methane hydrate destabilization due to earthquakes (see the poster at the bottom of the page on seismic activity).

With this in mind, let's take a look at the most recent picture of Earth.

September 13, 2013, 3am - Sep 14, 2013 1am [ click on image to enlarge ]

The large number of yellow spots in the top left corner are related to the flooding in the Basin of the Amur River (Heilong Jiang). Such extreme weather events are becoming ever more prominent, due to global warming and the feedbacks such as methane releases. Similarly, extreme weather events such as droughts and heatwaves lead to wildfires that also produce large amounts of methane.

The image only shows the Northern Hemisphere, but on the Southern Hemisphere, high levels of methane have been recorded for a long time on Antarctica. While huge amounts of snow fall on Antartica, the amount of snow and ice that melts each year is even larger, widening the difference between the weight the snow and ice exercize between periods. This difference in weight could similarly cause rebounds of the Earth's crust, sucking up the magma and causing methane hydrates to be destabilized, as described in the earlier post Antarctic methane peaks at 2249 ppb.

The image also shows fault lines. Several yellow spots are present on the fault line over the Arctic, including some that point at the coast of Norway; they appear to be caused by seismic activity along the fault line, as discussed in the recent post Methane reaches 2571 ppb.

Meanwhile, methane readings peaked at 2416 ppb on September 14, 2013. Very worrying are also the high methane readings close to the Gakkel Ridge, the fault line at the center of the Arctic Ocean, and the spots closer to the Laptev Sea.

Finally, there are high readings along the Aleutian Islands, Alaska. The islands, with their 57 volcanoes, are in the northern part of the Pacific Ring of Fire and they have experienced a lot of seismic activity lately, including an earthquake with a magnitude of 7 on the Richter scale on August 30, 2013, and several more recent earthquakes with a higher magnitude than 6 on the Richter scale.

[Editor: The images below, added September 24 and 26, 2013, show high methane releases at a spot just north of Greenland that was hit by an earthquake with a magnitude of 4.5 on the Richter scale on September 1, 2013, as also discussed in the post Methane reaches 2571 ppb. The two bottom images also show the magnitude 5 earthquake that hit Russia on September 24, 2013.]