Links between earthquakes and other geologic activity

Nature Geoscience (August volume 6(8), pp. 585-672) has a fairly long section ("a Web Focus") and a number of papers on geologic activity associated with or triggered by earthquakes. The introductory editorial reflects that in 1835 Charles Darwin voyaging on the Beagle experienced a large earthquake near Concepcion, Chile, and noted that within the hour a train of volcanoes in the Andes spouted out a dark column of smoke (though it would take a journey into Darwin's notes to determine whether he thought this was volcanic gas or perhaps debris from landslides. The implication in the editorial is that it was the former).
   

Illustration of the elastic rebound part of volcanic arc
subsidence after a megathrust earthquake

The first paper in this section (by Sigurjon Jonsson) summarizes the deflation of volcanic areas in response to the 2011 Tohoku and 2010 Maule (Chile) earthquakes. Both settings are at subduction zones (see figure), and the volcanoes that subsided were on the overriding plate. Prior to the earthquake, strain accumulates and compresses the overriding plate. During and after the earthquake, the overriding plate extends and subsides. However, subsidence beyond that which can be explained by this process is observed.
     In the case of the Tohoku earthquake, Takada and Fukushima documented 5-15 cm of subsidence at a distance of 150-200 km from the rupture earthquake, but no volcanic eruptions. They suggest that subsidence is caused by sinking of magma reservoirs and their warm host rocks through the colder surrounding crust. Prichard and colleagues noted that two earthquakes (1906, 1960) were followed by eruptions in the Andes within a year, but that no eruptions have been clearly associated with the 2010 earthquake. They were, however, able to document the 15 cm of subsidence, and suggest that hydrothermal fluids were released from hydrothermal systems surrounding the volcanoes in Chile during the 2010 quake, and that the escape of these fluids caused the volcanic areas to deflate.
     A second example of a proposed connection between earthquakes and geologic activity is more controversial: the Lusi mud volcano eruption. In 2006, mud erupted through and around a drill hole, flooding towns and displacing thousands of people.  Paul Davis summarizes a paper by Lupi et al. that proposes that the 2006 Lusi mud eruption in Indonesia (still continuing) was triggered by a M6.3 earthquake two days prior to the eruption and 275 km away.  Lupi et al. argue that strains, which are unarguably small at such a distance in homogeneous media,  were amplified by a downward concave layer of shale that acted as a parabolic reflector. Their simulations suggest that the stresses could have been about 100 kPa, five times higher than original estimates of 21 kPa. Such pressures, the assert, could have liquified the mud that resides at depth, resulting in the eruption of mud through the drill hole. This conclusion remains controversial (see discussion by R.J. Davies, et al., Earth and Planetary Science Letters, 272, 627-638, 2008).
     For a third example, Fischer et al. examine subduction zone earthquakes as triggers of submarine hydrocarbon seepage.  Offshore of Pakistan, the Arabian Plate subducts beneath the Eurasian plate. This is a region of intense seismicity, in particular a major earthquake (M8.1) occurred there in 1945. It occurred in an area where gas hydrates (methane clathrates) are present, and leakage of hydrocarbon gas is known to occur here. Methane and sulfates both occur in the ocean with sulfate being stable above about 5 mbsf, and methane at greater depths. The concentration of both goes to nearly zero at a depth known as the sulfate-methane transition (SMT). In a complicated chemical reaction, sulphate is consumed through anaerobic oxidation of methane (CH4 + SO24􏰀 ! HCO􏰀3 + HS􏰀 + H2O). Barium, being present in sea water, is precipitated at the SMT in so-called "barite fronts" and the abundance of barite can be used to reconstruct changes in upward methane flux.  The authors calculated that it would take approximately 38-91 years to produce the observed barite enrichments. This leads them to conclude that the barite production could have been initiated by the 1945 earthquake and an accompanying increase in methane flux due to release from the hydrates. If confirmed, submarine gas release triggered by earthquakes needs to be added to the list of processes that can add methane to the hydrosphere, and possibly to the atmosphere, in the carbon budget.




References: Takada, Y., and Fukushima, Y., Nature Geoscience, 6, 637-641, 2013.
Pritchard, M.E., Jay, J.A., Aron, F., Henderson, S.T., and Lara, L.E., Subsidence at southern Andes volcanoes induced by the 2010 Maule, Chile earthquake, Nature Geoscience, 6, 632-626, 2013.
Lupi, M., Saenger, E.H., Fuchs, F., and Miller, S.A., Lusi mud eruption triggered by geometric focusing of seismic waves, Nature Geoscience, 6, 642-646, 2013.
Fischer, D., et al., Subduction zone earthquake as potential trigger of submarine hydrocarbon seepage, Nature Geoscience, 6, 647-651, 2013.

Beautiful, beautiful volcanic picture!

Klyuchevskaya Volcano, December 4, 2010 as observed by the Advanced Land Imager (ALI) aboard Earth Observing-1 (EO-1) satellite. You can link to a high resolution image that covers a larger area here.

This is one of those "worth a thousand word" pictures.  Rarely have I seen a photo in which the atmosphere is so clear around a volcano, the winds are so calm, the lighting is so perfect, and the eruption so striking.  No scale is given for this particular photo, but it is one of a series that have been rising to nearly 8 km (26,000 feet) from Klyuchevskaya.  Perhaps even more striking than the plume is the beautiful collar of pileus clouds surrounding the higher flanks of the mountain. Pileus is the Latin word for "cap". They form when updrafts push up moist air from lower altitudes.  In rising, the air cools to its dew point, causing droplets to form and create the cloud. Pileus clouds often form over cumulus clouds, and over rising plumes themselves as shown in this post about the eruption of Sarychev Peak volcano.

Volcanic plumes have two parts. Near the vent from which they emerge, the ascent of the plume is driven by momentum.  Further away from the vent, the plume rises buoyantly, and at high elevations (not shown here), some plumes form an umbrella. My guess is that this one did not. Plumes transport volcanic ash.  Near the plume, the primary control on ash dispersal is the plume itself--it's momentum and buoyancy characteristics and, to some extent, its interaction with the atmosphere as air is entrained into the eruption column.  Further away from the plume, atmospheric structure and winds control the dispersal of ejecta.  An excellent reference on volcanic plume dynamics is "Physics of Explosive Volcanic Eruptions", Special Publication 145 of the Geological Society of London, edited by R.S.J. Sparks and J.S. Gilbert, 2002.

Santorini volcano

Santorini calder in the Aegean, Greece
Photo by Aster aboard the Terra spacecraft, NASA

Santorini Volcano erupted about 30 cubic kilometers of magma in ~1650 B.C. The ash column is estimated to have risen to ~36 kilometers (~22 miles).  The eruption of such a large volume left a large caldera (the whole image is 18 x 18 km). There has been much speculation that this eruption is the source of the myth of the lost land of Atlantis.  The largest island is There, the next largest is Therasia, and the small islands in the center of the caldera are the Kameni Islands, which are the site of ongoing mild activity.  The most recent eruption was phreatomagmatic eruption in 1950, in which phreatic activity preceded the effusion of lavas.  There may have been a precursor to this island as early as 197 BC, but the current island appears to have started in 46 AD.  Interestingly, it was described by a number of the Roman historians, including Pliny the Elder, who would die 33 years later in the eruption of Vesuvius.

Volcanoes and atom bombs

Photo of Matua volcano, Siberia, taken by NASA astronauts

Detonation of a thermobaric (fuel-air) bomb by the Russians.
Believed to be the largest of its kind ever detonated.

The New York times recently had a photo documentary of development of the atomic bomb. The photo below is of a "fuel-air bomb", often called a "vacuum bomb". This type of explosive uses oxygen from the surrounding air to increase the duration, and destructiveness, of the shock waves/fireball. They were first developed by the Germans during WWII, and are in use by modern military and in guerilla warfare (1993 World Trade Center bombing, 2002 Bali bombings).

Some volcanoes have eruptions that are "explosive" enough to produce shock waves.  These were first recognized by Perret during explosive eruptions of Vesuvius in 1906, and were later observed and analyzed quantitatively at Ngauruhoe, New Zealand (Nairn, I.A., Nature 259 (5540, pp. 190-192, 1976). On June 12, 2010, NASA astronauts were able to capture the photo at the left of an eruption of Matua volcano, Siberia.  You can't see the shock wave directly, but can see the hole that it punched through the cloud deck.  The rising ash plume has also pushed up a layer of moist air forming a pileus "cap cloud".  A pyroclastic flow is visible at the base of the column, descending toward 5 o'clock on the flank of the volcano.  Volcanologists use some of the same basic concepts about shock waves that were developed to analyze shocks from atomic bombs, and although we talk about the energy released in eruptions in terms of "kilotons" or "megatons". For example, I analyzed the energetics of the lateral blast at Mount St. Helens in 1980, and concluded that about 24 megatons of energy was released during the blast (Kieffer, S.W., Nature, 291, 568-570, 1981).

Pacaya Volcano, Guatemala, is erupting

This photo is from Wiki on May 28, 2010, attributed to the USGS from the site http://www.ngdc.noaa.gov/hazard/slideset/28/28_576_slide.shtml


According to CNN, Pacaya Volcano, 15 miles south of Guatemala City, began erupting at 9:00 p.m. ET on Thursday, May 27. Two villagers and a reporter from a CNN affiliate were killed in the initial eruption, crushed by rocks spewed from the volcano. 1800 people have been evacuated, and the airport in Guatemala City is closed as of Friday. Pacaya was dormant for a century until 1965, and has been active since then. The government has declared a 15 day state of emergency.

Pacaya is a young volcano, dated back to 23,000 years. It lies on the edge of an older larger caldera formed at least 300,000 years ago. It has erupted at least 23 times since the Spanish colonization in the 15th century. It is one of the many Central American volcanoes associated with the subduction of the Cocos Plate beneath the Caribbean Plate.

Volcanic Mesocyclones and Lightning

Mount Pinatubo erupted in 1991. Nearly 20 years later, scientists made careful measurements of the position of the top of the eruption column, the "umbrella", and noted that it rotated (see Chakraborty, P., Gioia, G., and Kieffer, S., Volcanic Mesocyclones, Nature, 458, 497-500, 2010). The rotation induced an instability manifested as waves or lobes on the edge of the umbrella, as shown in the attached figure (from the Nature paper). The image shows a satellite view of the umbrella of Pinatubo. The graph shows rotation rate and growth rate of the umbrella.

The two sketches above show the outline of the edge at different times as documented by satellite photos, and the graphs in the lower left show measured rotation rates. Details are in the Nature paper.

By analogy with meteorologic cyclones, Chakraborty et al. called the eruption plume a "volcanic mesocyclone". Three key elements interact to produce tornadic structures such as dust devils and waterspouts: updraft in the center, downdraughts, and the rotating mesocyclone. Chakraborty et al. proposed that the mesocyclone pulls the ash radially outwards from the core of the updraught, gathering it in an outer sheath where it discharges to produce the spectacular lightning displays that can accompany volcanic eruptions. The color image shows such lightning in the current eruption of Eyjafjallajokull in Iceland. It was taken by Marco Fulle. The other image shows (a) waterspouts spawned during the eruption of Surtsey volcano on November 14, 1963, and (b) the lightning sheath from Mount Chaiten on May 3, 2008.

Contact me at s1kieffer@gmail.com if you would like a PDF of the Nature paper.