Why Earth-centrics are always going to be surprised

Posted on March 13, 2007 by Chris Rowan

Planetary geology is going through a really fertile period at the moment, with numerous probes and rovers sending back mouthwatering images and data from many different parts of the solar system. However, as well as being extremely interesting in its own right, the information being sent back also highlights an important general point for all us geologists: the dominant processes which shape the Earth are not necessarily the same, or as important, or even present, on other planetary bodies.

An example: what do you need for a planet or moon to be volcanically active? Just from looking at how volcanoes work on Earth, you’d say that it needs to be above a certain size, so that it retains enough internal heat (left over from its formation, and from radioactive decay) to sustain mantle convection.

Earth with a diameter of 12,800 km, is large enough to still be volcanically active: Mars (diameter 6800 km) and our Moon (diameter 3400 km) are too small. They were once, but have now lost too much heat and are volcanically dead. However, as this fabulous picture from the New Horizons probe shows, Io (diameter 3600 km) breaks the rules, and not in a small way either: Io is the most volcanically active body in the solar system.

Io_volc.jpg

Continue reading →

Categories: planets

The five stages of peer review grief

Posted on March 12, 2007 by Chris Rowan

In the midst of all the good things that have happened to me recently, I also got some rather less cheerful news: a couple of papers I submitted way back in the middle of last year finally arrived back in my in-box covered with a large dollop of the peer review equivalent of red ink attached. Even in my nascent academic career, this isn’t the first time I’ve got a negative review – indeed, by sending something out to peer review you’re inviting criticism, in a way – but it’s never a particularly pleasant experience, especially when you’re talking about the end product of four years of struggle and head-scratching.

Despite the numerous distractions of the last three or four weeks, the reviews, and what I can or want to do in response to them, have been fairly continuously in the back of my mind, and my attitude has gone through a number of distinct phases:

  • Shock and Denial.
    (Skim numbly through the decision letters. Words like ‘reject’ and ‘major revisions’ stand out in burning characters on the page)

    They can’t be that bad, can they? I can’t have patiently waited for 8 months just to get told to get lost, can I? Perhaps it’s just one particularly negative reviewer, or there’s just one or two points of contention which I can defend robustly and win the editor over.
    (Looks at length of attached commentary. Notes that Associate Editor is someone quite prominent in the area I’ve been working on)

    Oh dear, maybe not…

    • Continue reading →

Categories: academic life, publication

Lusi Latest

Posted on March 12, 2007 by Chris Rowan

The latest from Lusi

After dropping 220 chains of concrete balls down the throat of Lusi, the man-made mud volcano, what dramatic results do the people who dreamed up this madcap venture have to report?

“If you ask me, it appears calmer, but that is a subjective view,” said Satria Bijaksana from Indonesia’s Bandung Institute of Technology, which devised the plan to slow the disastrous mudflow.

So in place of objective measures like, I don’t know, changes in the eruption rate, we get a mood assessment. They’ll be trying aromatherapy next…

Source

Categories: geohazards, Lusi

Seismic triggering of volcanic eruptions: from Darwin to today

Posted on March 9, 2007 by Chris Rowan

My last post on possible triggers for volcanic eruptions left a hanging question: why do seasonal variations in crustal loading seem to have an effect, when those resulting from tides do not? It’s not like the forces and strains involved are any larger – if anything they’re generally smaller. The key seems to be the timescale over which they are applied. Modern views of magma chambers are moving away from the idea that they are a large, homogenous blob of molten rock; instead the magma is “mushy”, with small, interconnected pockets of melt within a more solid matrix. This structure means that the molten parts are insulated from the effects of a short, sharp force, which is absorbed by elastic deformation in the solid parts; only a force consistently applied over a substantial length of time will cause the pockets of melt to be squeezed and moved around. See here for more discussion of these ideas, with reference to an Alaskan volcano.

Based on that, you’d expect the effect of earthquakes on the timing of volcanic eruptions to be negligible too – the passage of seismic waves through a magma chamber is a short, sharp shock rather than the longer term change which seems to be required. Evidence that this might not be the case came to my attention from an unusual source -from reading This Thing of Darkness by Harry Thompson, which is based around the voyages of the Beagle, including but not restricted to the one which Darwin sailed on. When I’m reading (or watching) fiction my scientific interest is usually only piqued when I notice a stupid error, or am confronted with a lame misunderstanding of an entire field (I am then forced to stop reading and engage in breathing exercises to control my blood pressure). In this case, however, I was fascinated by a passage in Chapter 22 (pages 366-67 of my edition) which describes how, as the Beagle sails up the west coast of Chile on the evening of the 20th February 1835, the crew observe the eruption of the Andean volcano Osorno. Further in the distance, two more volcanoes also start erupting, and later the Beagle is shaken by the passage of a tsunami, which we later find out was caused by a massive earthquake which flattened Concepcion. The clear implication that multiple volcanic eruptions along the Andean chain had been triggered by this earthquake
Continue reading →

Categories: earthquakes, geohazards, geology, paper reviews, volcanoes

External triggering of volcanic eruptions

Posted on March 8, 2007 by Chris Rowan

From ye olde blog: in August last year, the BBC website published a rather silly story story discussing the possibility that an imminent full moon would trigger an eruption of Mount Mayon in the Phillipines. It didn’t, and Phil Plait at Bad Astronomy was suitably mocking about the rather poor science behind this claim, but I felt a bit more could be added from a geological perspective: are there external factors which can predictably influence when a volcano erupts?

We need to be careful about what this story is and isn’t about. What it’s not about is the notion that a completely inactive volcano is suddenly going to be woken up; it’s more about the potential of tidal forces to act as a trigger for a volcano which is already predisposed to erupt (e.g. has a full magma chamber under pressure). As the earth rotates beneath the Moon, its gravity not only pulls on the water directly beneath it, but also stretches the underlying crust. The effect is small, but it could be enough to destabilise a finely balanced system and cause an eruption.
Continue reading →

Categories: geohazards, geology, paper reviews, volcanoes