Tuesday, June 24, 2014

Klyuchevskaya Sopka

Hell yeah, that’s a volcanic eruption as seen from space.

To be more precise, it is the eruption of Klyuchevskaya Sopka taken by the Space Shuttle Endeavour on the 30th of September 1994.

Impressive, isn’t it eh?

This particular eruption expelled ash and gases upwards of 18,300 metres above sea level and the winds carried the ash as far as 1,030 km. Looking at this image and reading just how enormous the eruption was, it is easy to understand why some people link current climate change with events like volcanic eruptions. But, what role do volcanoes actually play?

As we can see, during major volcanic eruptions huge amounts of volcanic gas, aerosols and ash are injected into the stratosphere. The ash tends to fall fairly rapidly from the stratosphere; a matter of days or weeks and has little implication on the climate. However, volcanic gases like sulphur dioxide can cause global cooling and volcanic carbon dioxide, the infamous greenhouse gas, has the potential to promote global warming.

Perhaps contrary to belief, the most significant climate impacts of volcanic activity are as a result of sulphur dioxide. Sulphur dioxide gas is converted to droplets of sulphuric acid in the stratosphere over the course of a week to several months after the eruption. Winds in the stratosphere spread the aerosols until they practically cover the globe. As the droplets have a high albedo, they reflect sunlight reducing the amount of energy reaching the lower atmosphere and the Earth's surface; cooling them. (NASA,1996)

Once formed, these aerosols stay in the stratosphere for around 2 years, although data from NASA’s stratospheric Aerosol and Gas Experiment (SAGE II) showed the effects of the eruption of Mt. Pinatubo in 1991 lingered for up to 10 years.

As mentioned previously, carbon dioxide is also emitted during volcanic eruption and a question that has commonly been asked is “Don’t volcanoes contribute much more CO2 emissions than human activities?

Unfortunately the answer to that question is a clear and unequivocal “No”.

Published reviews of the scientific literature by Kerrick et al (2001) report a minimum-maximum range of emission of 65 to 319 million tonnes of CO2 per year from subaerial and submarine volcanoes.

This seems like a huge amount, and it is. That is, until we compare it to anthropogenic emissions.

According to an International Energy Agency some 30. 6 billion tonnes of carbon dioxide were released into the atmosphere as a result of human activity in 2010.To say that another way, assuming the highest estimates of volcanic CO2 emissions (319 million tonnes), human-emitted carbon dioxide levels were more than 95 times higher.

The Mount Pinatubo eruption in 1991 emitted 42 million tonnes of CO2 (Gerlach et al 1996). Now, compare this to human emissions in 1991 which were a total of 23 billion tonnes of CO2 (CDIAC). The strongest eruption over the last half-century amounted to 0.2% of human CO2 emissions in that year. 0.2%.

Image courtesy of NASA


Carbon Dioxide Information Analysis Centre:http://cdiac.ornl.gov/trends/emis/overview_2006.html

Kerrick, D. M. (2001). "Present and past nonanthropogenic CO2 degassing from the solid earth." Rev. Geophys. 39(4): 565-585.

NASA,1996; “Atmospheric Aerosols: What Are They, and Why Are They So Important?”

Terrence M. Gerlach(1996) Pre-Eruption Vapor in Magma of the Climactic Mount Pinatubo Eruption: Source of the Giant Stratospheric Sulfur Dioxide Cloud . http://vulcan.wr.usgs.gov/Projects/Emissions/Reports/Pinatubo/pinatubo.html

Annular Eclipse

Almost 14 days ago, there was a lunar eclipse visible in the Western Hemisphere. A lunar eclipse takes place when the Earth is directly between the Moon and the Sun. It takes the Moon 28 days to orbit around the Earth, so 14 days after a lunar eclipse, the Moon is on the opposite side of the Earth, between the Earth and the sun.

If the angles line up correctly, that’s the day when a solar eclipse is possible, and on April 29th, there will be an annular eclipse of the sun. Unfortunately the eclipse will be best viewed from remote areas in Western Australia, the southern Indian Ocean, and Antarctica, but populated areas in Eastern Australia may be able to see up to about 60% coverage just before sunset on Tuesday.

An annular eclipse occurs when the Moon blocks out most, but not all, of the sun’s disk. The moon’s orbit around the Earth is not circular, so at some times it’s closer to the planet and other times it’s farther away. An annular eclipse happens when the moon is at a point in its orbit far from earth, making the moon’s disk small enough to allow this “ring of fire” around the edge.

As with most eclipses, it is not safe to view this eclipse with the naked eye; you will cause eye damage if you look. Standard sunglasses also do not provide enough protection. Instead, eclipse-viewing glasses, welding shields, cameras, or other viewing devices will be required for save viewing.

Image credit: t-mizo (creative commons license): previous annular eclipse viewed from Japan

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Nohkalikai Falls

During the monsoon season, this area of the north eastern Indian state of Meghalaya near Cherrapunji has been named the wettest place on Earth. All that water has to go somewhere, and several of the Subcontinent's tallest falls are located in the area. The monsoon gathers during the spring as the land bakes, causing a column of rising air that pulls moist sea air behind it, bringing the annual rains on which Indian civilisation has depended since pre Vedic times.

Nohkalikai is supposedly the tallest plummet in India, at around 340 metres, and at the right time of year one of the most powerful. The crashing waters have carved out a deep rock pool at the bottom of the plateau that changes colour from blue to green depending on the season. The rocks are a Cretaceous-Paleogene sedimentary stack made of limestone and sandstone.

The name (jump of Ka Lilai) is associated with a tragic legend of a woman who went mad after a family tragedy and threw herself off the cliff. During the dry season thee falls slow to a trickle. They sadly often hide in cloud during the monsoon season when at their most spectacular.

Image credit: Sunanda

Fire Whirls

While I prefer the traditional name to the hyped one currently doing the rounds of the internet, these relatively short lived flaming twisters are an interesting phenomenon, and they may become more common as wildfires get more frequent and intense due to global warming. They usually only last a few minutes, though during the 2003 wildfires near Canberra in Australia, one is known to have left a 25km swath of burnt snapped trees and overturned cars after a 250kph fiery twister formed in oil rich eucalypt forest.

They form, like all vortices in whatever medium, when two masses in different states meet at speed. With tornadoes, warm moist air is meeting cold dry air in the turbulent conditions of a supercell thunderstorm. During wildfires, the intense heat and turbulent contrast with the surrounding air can be enough to create these twisters, and sometimes sustain them for quite awhile. The vortex also sucks up combustible gases from the fire (such as evaporated tree resin), which ignites in the oxygen rich centre of the vortex, giving the twister another dose of energetic fuel. They can also spread the fire by whirling burning debris far and wide.

A similar phenomenon was responsible for the Hamburg firestorm in 1943, when several days of incendiary bombing ignited a self sustaining enormous conflagration that took weeks to burn itself out fully.

Should any of our readers ever see one of these, do NOT go closer in order to get a photo, they behave unpredictably, and discretion being the better part of valour, please run away as fast as is safe. Bushfires in general are best avoided at all times, unless you're a dedicated fire fighter.

Image credit, taken in Missouri: Janae Copelin/Barcroft USA


The geology of Carnac

Its summer solstice today, and as is my wont I present one of the prehistoric wonders of the world, the 10,000+ aligned standing stones of Karnac In Brittany (France, though some of them don't agree). These are the prototypical menhirs, as carved by Obelix, one of my heroes since childhood.

They were carved from the tough granites and gneisses of the Armorican Massif, the roots of once tall mountains that have been remobilised (ie grew and were eroded again) a full three times. The first was the Cadomian half a billion years ago followed by a complex series of tectonic events as the supercontinent Pangaea assembled during the Devonian and Carboniferous between 400 and 280 million years ago. Armorica started off life as the northern shore of Gondwana, before rifting off and colliding with Laurussia during the Hercynian event. The assembly of Pangaea when Euramerica collided with Gondwana in the Variscan orogeny completes this continental dance of mountain creation.

Each event was accompanied by extensive metamorphism, melting of both sedimentary and volcanic rocks into granite as they were buried under the pressure and heat of rising mountains and subduction related volcanism as ancient oceans closed. Since then of course Pangaea has split up, and the once proud peaks have been ground down by erosion, so that the tallest rise in the region is a mere 480 metros.

Legend states that they are a Roman legion, transformed into stone by the wizard Merlin, though they date from the Neolithic period around 4,500-2,000 BCE, long before the Celtic peoples moved west from their probable heartland in the Danube. Dating their erection is difficult, since little organic matter was buried under them for C14 data but the peak is thought to have been around 3,300 BCE. They are the largest assemblage of menhirs in the world, spread out over a wide area.

There are three main alignments related to the solstice sunrise and sunsets at both ends of the year, known as Menec, Kermario and Kerlescan in the local Breton language, though they may have formed as single grouping as stones have been removed over the millennia for building and other purposes. All of them have taller stones to the west (the traditional direction of death) and shorter ones to the east (that of birth).

Previous posts in this series:
The geology of newgrange: http://tinyurl.com/qhj3e4v
The geology of Stonehenge 1&2:http://tinyurl.com/kec8tu3 andhttp://tinyurl.com/nbaq8v5

Image credit: Jim Brandenburg via wallpaper downloader