Spot the planetary difference

There are many differences between Titan’s atmosphere and Earth’s, in terms of temperature (a couple of hundred degrees lower) and composition (no oxygen, more methane), but the cloud formation recently snapped above Titan’s north pole by Cassini, shown in the top image above, doesn’t look too dissimilar from storms snapped from our own planet’s orbit, as the lower image (source) illustrates. At 2400 km in diameter, it is quite a whopper - it would fill most of the North Atlantic.

It’s not that clouds haven’t been imaged on Titan before; we managed that even before Cassini arrived in Saturnian orbit, and Cassini itself has imaged some before now as well. But those previously observed cloud systems were mainly located around the south pole of Titan; what’s interesting about this one is that it is in the opposite hemisphere, directly above the lakes which have caused so much excitement. This makes it extremely tempting to link the two phenomena. The northern hemisphere of Titan is now entering its spring after a seven-year winter, so evaporation from these lakes in the rising temperatures could easily have contributed to the formation of clouds.

The key question, though, is what happens then: do significant amounts of hydrocarbons rain back out of the atmosphere to complete the “methanological cycle”? Is this precipitation intense enough be actively eroding out the landscapes imaged by the Huygens lander on its descent, and produce standing bodies of hydrocarbons in depressed topography? Or, rather than being refilled from above, are lakes on the surface more to do with hydrocarbon release from either subsurface “methanifers”, or cryovolcanic venting?

Some of these questions are still open. During Huygen’s descent, it measured variations in atmospheric methane concentration and temperature which, when examined in detail, indicated the presence of thin methane clouds capable of generating a persistent light drizzle [1]. Such weather makes the surface of Titan the natural location for any British extraterrestrial colony, but it is not really energetic enough to carve new drainage channels or any other new topography. And although attempts to model Titan’s atmosphere do suggest that strong storms can occur [2], how common or important they are in reality is unclear. Effectively, what we need is more observation time. Just like continuous observations of Mars over several years have revealed changing features which might indicate actively flowing water, if Cassini is able to observe Titan for long enough, we might not only see a few storms but also be able to assess their effect on the landscape.

[1] Tokano et al., 2006. Nature, 442, 432-435, [doi].

[2] Hueso and Sánchez-Lavega, 2006. Nature, 442, 428-431, [doi].

This post was published on Day 1 of the Just Science challenge – a full week of science and only science. You can subscribe to the RSS feed at http://www.justscience.net/?feed=rss2.
All my posts for this week

Prepare for 7 days of pure science

After a lot of dithering, I've signed myself up for the Just Science Challenge:

we would like to propose a Week of Science, to begin on Monday, February 5, and end on Sunday, February 11. During that time each blogger should post about science only, with at least one post per day. Furthermore, issues which are favored by anti-scientific groups (creationism, global warming, etc.) should be either avoided, or discussed without reference to anti-scientific positions.

I like to think I am fairly science-focused anyway, or at least that my digressions into other realms do not overwhelm the geology. But I like the idea of having a week where we don't let creationists, denialists and the other forces of antiscience dictate any of our output. Besides, it's always nice to stretch myself, and a post a day is enough of an increase in my average output to be a nice challenge, even if I've cheated a little by putting in a fair amount of preliminary groundwork.

A day in the life

Lab Lemming wants to know what I do in a typical day. I’m not sure I have a “typical day”, but today is as good as any other I suppose.

Job title: Paleomagnetism technician (bear this in mind for what follows)
Insitution: School of Ocean and Earth Sciences, National Oceanography Centre, Southampton.
Date: Friday 2nd February, 2007

Prevailing conditions:

• The deadline for handing in the third year mapping projects is Monday
  
• Semester 1 exams have just finished
  
• Our cryogenic magnetometer is not being used this week because we need a helium refill (which was going to be done this morning but has been put back to Monday).

8:30-8:45: Walk into work
8:50: Switch on my computer and open exam paper to mark.
8:55: Computer beeps – student has e-mailed wanting me to check their map before they print it
8:55-9:15: In computer room consulting with stressed and sleep-deprived student.
9:20: Get back to my office to find another pile of exam scripts on my chair. This lot really liked my question, it seems.
9:20-10:00: Marking
10:00-10:15: Another student wanting help with his cross-sections
10:30-10:45: Yet another student; this one wants his report abstract checked, and reassurance regarding the word limit.
11:00-11:20: In lab to show a fourth year undergraduate how to do susceptibility measurements (for their dissertation project).
11:30-11:45: Get fed up with constant interruptions and go and have coffee.
11:50-12:00: Dragged back to the lab by panicky student who thinks she’s broken the computer. She hasn’t, it’s just so old (DOS, no less) that she doesn’t really get how it works.
12:00-12:45: Marking.
(12:25: Course co-ordinator pops in to check that I have got the latest batch of exam scripts. He’d like them back early next week (!) )
12:45-12:50: Some more students, this time people doing 4th year dissertation who want to book some lab time.
12:50-1:30 pm: Lunch.
1:30-2:45: Finally get a moment of quiet to get through some marking. Promisingly, most appear to be written in a language resembling English.
2:45-3:00: Start sending out e-mails about laboratory schedule for the coming weeks (given that it’s going to be chaos when I leave, I want to make sure everyone has some machine time).
3:00-3:30: Reinvaded by stressed students.
3:30-3:45: A bit more marking.
3:45-4:30: More mapping consulation down in the computer room with even more stressed and sleep-deprived students.
4:30-4:45: Need caffeine.
4:45-5:00: Work on lab schedule for those who have bothered to respond to my e-mails.
5:00-5:30: Finalise marks on first exam question. Two more to go!
5:30-5:45: Tidy stuff up before heading to the pub for a well-earned pint or three.

It’s not like this every day – Thursday was spent mainly trying to sort out someone’s misorientated sample data, Monday will mainly be spent sorting out the helium refill. The common theme, perhaps, is that of me doing a lot running about on other peoples’ behalf.

I’m passing this on to Transient Reporter (assuming that he’s not snowed under changing nappies, I don’t really want to hear about that) and Thermochronic, but everyone should pile in. Now, where's that pint...

Linking up

Philosophia Naturalis #6 is up at Science and Reason. Lots of physical science goodness, but scandalously no geology - which is at least partly my fault for not getting around to submitting any suggestions. Perhaps our growing band of geobloggers should fortify ourselves with gin and tonic and gatecrash next months edition at Geek Counterpoint.

On that subject, you may or may not have noticed the new occupant of my sidebar - an amalgamated feed of recent posts from all the geobloggers I'm aware of, created using Google Reader's nifty 'share' function. I thought it was a convenient way of making all (any) of my readers aware of what everyone else in the geoblogosphere is up to. At the rate it's been ticking over in the last week, quite a lot.

Anyone is welcome to hijack the feed (if you can't find the relevant script in my source page, let me know and I'll send it to you) - the more cross-linking the better for all of us, I reckon. And if you write (or know of) a geoblog I've yet to include, drop me an e-mail.

Lusi – the man-made mud volcano

The latest from Lusi

In May 2006, an exploratory gas well being drilled in eastern Java hit a limestone aquifer. Because the lower part of the well had not yet been ‘cased’ - sealed off from the surrounding rock - a surge of overpressured water was released into the mudstones higher in the borehole, fracturing them and mixing them into a hot mud which eventually made its way to the surface near the drilling rig.

Since then, since then, 7,000-150,000 cubic metres of mud* a day has been disgorged from a vent dubbed ‘Lusi’, burying surrounding villages. I found this video on You Tube showing the encroachment of the mud – a rising tide which shows no sign of stopping.

From a more elevated perspective, here’s a satellite image. I think those huts on the bottom left of the second panel are the ones you see at the end of the video


This is from a recent GSA Today paper by Davies et al.[doi], which confirmed that the drilling into the aquifer was probably responsible for the eruption; the company operating the well (understandably) tried to implicate an earthquake which occurred two days beforehand, but any seismogenic effects should have been immediate (and detectable as a pressure change in the borehole), and ‘liquefaction’ tends to affect less cohesive sands more than mud.

You can read more on this at PhysOrg. Then read how they’re planning to put a stop to it:

Indonesian geophysicists hope to stem the flow of a destructive mud volcano on East Java by dropping chains of concrete balls into its mouth…

… Last week, the government team tackling the disaster approved a plan that will use 1,000 steel chains to try to slow the flow of mud. Each chain is 1.5 metres long and links together four concrete balls — two that are 40 centimetres across and two that are 20 centimetres across. Each ball and chain set will weigh about 300 kilograms. The balls themselves will be modified to maximize their friction with the mud.

Apparently, they think this will restrict the flow without just causing it to divert somewhere else. I suppose it depends on how fractured the rock is, but I’d say it’s a long shot at best.

Update:And, a month later, this rather bizarre plan swings into action. On Saturday, they only managed to drop one chain because a steel cable on the hoisting mechanism broke. They managed sixteen more on Monday, but then they hit another potential snag when they looked at the telemetry from sensors attached to the chains, as another site has reported under the arresting title ‘Volcano consumes concrete balls’:

The balls slid one kilometre into the crater, roughly twice the depth anticipated, so many more than planned may be required to staunch the mudflow, said the operation's spokesperson Rudi Novrianto.

"Based on our monitoring of Monday's operations, we may later decide to add to the number of ball chains, but the decision will only be made once the initial target of 374 chains have been dropped into the mud hole," he said…

…Basuki Hadimuljono, the head of the team trying to plug the steaming crater, was quoted by the Koran Tempo newspaper as saying that the number of chains required may rise to 1 000 from the initial estimate of 374.

I remain unconvinced that this is going to work, but you can’t fault their perseverance.

(Thanks to Geology News for the heads-up which led to the update).

*In media units, that’s up to 40 olympic swimming pools.

Fiddling while my blog burns

I've been putting off the switch to the new blogger template system because, like Propter Doc, I've been having trouble getting the expandable post summaries to work properly. Rewriting the javascript which did the trick on my old template to use the new metadata labels, and get past a seemingly much fussier XML parser, proved to be a long exercise in fiddling, but I've finally managed it. For those who are interested, this is the code I used. You have to be in the HTML view with the widgets expanded to insert it:

<script type='text/javascript'>
var memory = 0;
var number = 0;
</script>

Then scroll way down the page until you find the div for the post-body and insert the stuff in bold:

<div class='post-body'>
<b:if cond='data:blog.pageType == "item"'>
<style>span.fullpost{display:inline;}</style>
<p><data:post.body/></p>
<b:else/>
<style>span.fullpost{display:none;}</style>
<p><data:post.body/></p>
<script type='text/javascript'>
var permlink='<data:post.url/>';
var title='<data:post.title/>';

var spans = document.getElementsByTagName('span');
var number = 0;
for(i=0; i <spans.length; i++){
var c = " " + spans[i].className + " ";
if (c.indexOf("fullpost") != -1) {
number++;
}
}

if(number != memory){document.write('<p><a href=' + permlink + '>"'+ title + '" continues...</a></p>') }
memory = number;
</script>

</b:if>

<div style='clear: both;'/> <!-- clear for photos floats -->

The bit in brackets in the document.write statement can be changed if you want it to say something different. Now, when you're writing a post, you just stick the bit you don't want to appear on your front page between <span class="fullpost"> and </span>, and off you go!

Note that I didn't write the original code - I've just (I think) bodged it to work in the new system. Here's another way to do it, from someone who looks like he might know what he's talking about, although for some reason I couldn't get that to work either.

I'll be fiddling with other bits of the template in the next few days, so apologies in advance for when I break the HTML (Update: which I see is already the case for IE users. Bloody Microsoft! OK, have fixed it (sort of) although all the posts vanish to the bottom of the page if you shrink the window too much. Seriously, people, get a better browser.

New data on the revision habits of the modern student

In one of the courses I taught last semester, the exam has asked pretty much the same questions every year for the last five years. This doesn’t exactly reflect well upon those doing the teaching, and this year (my second of covering these lectures) I made a deliberate decision to do something a bit different with the questions from my part of the course. The exam is divided into two sections: a ‘numerical’ part focussed on data manipulation and calculating things, and an ‘essay’ part. For the former, instead of asking the usual question about triple junction stability and migration, I gave them a question where they had to assess the quality of some paleomagnetic data and use them to calculate when a terrane (a highly allochthonous one, no less) collided with a larger continent.

I realised at the time that this alteration could potentially act as a useful survey of the study practices of our undergraduates. The question I set was actually pretty easy – if you’d bothered to revise the part of the course about paleomagnetic field tests and calculation of paleolatitudes (I’d even, after some debate, given them the relevant equation, and therefore wondered if it wasn’t a little too easy). However, students in thrall to the art of ‘question spotting’, who only revised the small bit of the course about triple junctions, might be in a little bit of trouble.

Today I received the scripts from the exam; no-one had answered my numerical question. Not one student.

Although that means I have less marking to do, part of me can’t help but find that a little bit depressing. The weird thing is, plenty of people answered one or both of the essay questions I set – both of which asked about parts of the course which previous years' questions hadn't, and at least one of which requires some knowledge of paleomagnetic techniques to answer properly. Maybe then, this just indicates a degree of mental inflexibility (‘It’s not a triple junction question! Panic!’) rather than damagingly limited revision practices. I suppose I’ll find out when I read the essays…

Update: OK, after a bit of investigation, it seems there are a number of factors at play here:

• Of the other two questions in the relevant section, one, on seismic moment and earthquake hazards, has been mixing and matching the same three subsections for at least the last four or five years; the other, on elastic bending of a plate in response to seamount loading, must have been seriously highlighted by the lecturer because I was asked to help with exactly the same question a week before the exams.
  
• I have some testimony to the effect that the students pretty much assumed that ‘my’ question would be of the same type as it had been in previous years (despite the fact that someone else had taught the course for most of those years), and revised (rather selectively) with that assumption in mind.
  
• If I’m scrupulously honest with myself, the way the question was worded might have made it seem that it was a lot more work than it actually was: not every step was explicitly spelt out, and the style (“This is the scenario. This is your data. Calculate stuff” style, rather than “Calculate x. Calculate y. Calcuate z.”) was perhaps a little intimidating. I’m open to the possibility I was also asking to much for a 45 minute question, but sadly I have no data to test that.
  

So, faced with two other questions they had prepared for, and one which they hadn’t and might have looked like a lot of work, the students opted to shun me. I’m not sure anyone comes out of this particularly well, to be honest. In my own defence, I have a fair number of essay questions to mark, so obviously I wasn’t being a fully bastard examiner from hell.

Milankovitch goes solar?

From New Scientist:

Robert Ehrlich of George Mason University in Fairfax, Virginia, modelled the effect of temperature fluctuations in the sun's interior. According to the standard view, the temperature of the sun's core is held constant by the opposing pressures of gravity and nuclear fusion. However, Ehrlich believed that slight variations should be possible [due to instabilities caused by interactions with the Sun’s magnetic field]…

…Ehrlich's model shows that whilst most of these oscillations cancel each other out, some reinforce one another and become long-lived temperature variations. The favoured frequencies allow the sun's core temperature to oscillate around its average temperature of 13.6 million kelvin in cycles lasting either 100,000 or 41,000 years. Ehrlich says that random interactions within the sun's magnetic field could flip the fluctuations from one cycle length to the other.

These two timescales are instantly recognisable to anyone familiar with Earth's ice ages: for the past million years, ice ages have occurred roughly every 100,000 years. Before that, they occurred roughly every 41,000 years.

The paper is up on arXiv, and his model also has an oscillation in the 22,000 year range as well. This strikes me as a mighty big coincidence; it’s not like we’ve pulled the frequencies of variations in the Earth’s orbit - the Milankovitch cycles generally held to control long-term climate fluctuations - out of thin air. One thing I’d really like to know how sensitive the periods of these solar oscillations, if they exist, are to changes in the temperature structure of the sun, which I suspect we haven’t constrained with absolute precision. That said, a solar oscillation in the 100,000 year range might solve the problem of why it’s such a dominant signal in the climate record.

Anyone care to guess how long it will take for someone to claim this somehow has a bearing on the reality of anthropogenic climate change?

Update: Those of you who don't see the disconnect should head over to Open Mind for a clear explanation of why we think that the current short-term warning we're all worried about cannot be attributed to solar variability)

The writing in the cave walls

There’s a really nice post up on RealClimate about extracting climate records from stalagmites. Stalagmites and other speleothems form when water, percolating down from the surface and picking up dissolved carbon dioxide and other minerals on the way, penetrates into a cave system. When it reaches the cool, dry air of a cave, the carbon dioxide can escape from solution and carbonate minerals precipitate out. Take a steady drip of water, leave for a few thousand years, and voila:


The exciting part comes when we look at a cross-section through a stalagmite: just like tree rings, chemical changes in the different carbonate layers - particularly changes in the oxygen isotope values – reflect changes in the water falling on the land above the caves when that layer was deposited, and hence potentially give us high-resolution information about climatic variations over tens of thousands of years. Even better, you can determine the age of deposition using uranium-thorium dating; so what we potentially have is a source of climate records comparable to those we can get from ice cores (allowing us to independently check their chronologies), but globally distributed; you get caves on every continent, not just Antarctica and Greenland.

One thing this lets us look at is the variations in the strength of the monsoon through the last few glacial cycles. In the northern hemisphere summer, air rising above the warming land draws in moist air from the oceans to the south. The resulting rain is isotopically light (it has a negative &delta¹⁸O) because it has become fractionated by more evaporation and transport. A longer, wetter, stronger summer monsoon should therefore lead to lighter groundwater &delta¹⁸O than a shorter, drier, weaker, one; and that is exactly what we see in stalactites in the relevant regions. Here’s a record for most of the Holocene from Oman [1], showing both long term (over thousands of years) and short-term (over decadal and centennial timescales) variations in monsoon strength:


And here’s a longer term record, going back through a number of 21,000 year precessionary cycles, compiled from three overlapping stalagmite records from the Hulu Caves in China [2]. This second figure also plots the average summer insolation (black curve), and the Greenland ice core &delta¹⁸O (which tracks temperature – blue curve). The correlation is very good (especially if you look at a better version of the figure) – suggesting that the monsoon is stronger when it is warmer in Greenland. Centennial scale variations in Greenland have been linked to changes in the themohaline circulation, so these data give us some indication of the global effects such changes can have.


The variations in the monsoon being studied in these papers is a very strong climate signal, but as measurement and analytical methods get more sensitive and sophisticated (for example, the Hulu record has recently been extended back to 180,000 years ago [3]), tracking smaller regional variations in climate will become much easier. These results clearly show how, as this recent Science editorial [4] argues, “the age of the speleothem” could be upon us.

[1] Fleitmann et al., Science 300, 1737-1739 (2003)
[2] Wang et al/, Science 294, 2345-2348
[3] Hai Cheng et al., Geology 34, 217–220, 2006
[4] Henderson, Science 313, 620-622, 2006

The vacuous quantify the nebulous (again)

The news on the radio this morning informed me that today is apparently most depressing day of the year.

Being contrary, I was actually feeling pretty good today. A proper weekend off, visiting some friends in Salisbury and visiting the Avebury stone circle, meant I actually had a fairly productive Monday. So, other than the continuing lack of news on the South African visitor permit front, the only depressing thing about today was the media's insistence on not only running with a supremely silly 'yes kids, in science there really is an equation for everything' story, but also recycling it from previous years.

If taking a few values we can quantify (debt and income levels, time elapsed since Christmas), at least as many which you most certainly can't ('general motivational levels'? 'the need to take action'? Please.) and randomly planting them in a forest of brackets wasn't vacuous enough, both the culprit (a serial offender it seems) and the media seem to have missed the fact that this magic formula was quite comprehensively falsified last year...