Chris: So, we both managed to survive another AGU. Is your brain full now?

Anne: Yes, it hurts.

Chris: But you seem to have had a pretty good week. Two well-received invited talks, and every time I saw you, you seemed to be talking science with other water-folk.

Anne: Your week ended on a high note, too. I saw you give an invited talk on New Zealand tectonics in a session on remagnetisation of sediments.

Chris: It was actually my first ever talk at AGU, and was a slightly more intimidating experience than a poster session. I think it went fine, although 5pm on the last day of the conference didn’t leave much time for feedback. At least I was better off than the person speaking just after me, who was not only giving one of the last talks at the conference, but had given one of the first at 8am on Monday.

What other interesting things did you see in the last couple of days?

Anne: On Thursday, I quite enjoyed the session I was in on post-eruptive processes on volcanic landscapes. I thought that the session conveners did a brilliant job of arranging the talks in a logical sequence, from explosive to effusive eruptions. They also did the smartest thing that I have ever seen during a time slot where a talk had been withdrawn: they used the time to allow people with posters in the session to give pop-ups advertising their poster.

Chris: That was a good idea. The poster hall is so massive that it’s quite easy to miss good stuff without some prompting. And I should know, I spent quite a lot of time in there the past couple of days. I saw a cool study on sedimentation in lakes close to the Alpine Fault in New Zealand – apparently fully 40% of the total sediment deposited is material mobilised during and just after earthquakes. And this morning I had a fascinating chat with Vincent Cortillot about using paleomagnetism to constrain the eruptive history of flood basalts – it seems that you can show that most of the material is erupted in short 100 to 1000 year pulses, and that how closely spaced in time these pulses are may explain whilst some large igneous provinces caused large mass extinction events whereas others did not. And amongst all the computer models of continental deformation, it was nice to see people still gaining useful new insights from physical models, with plasticine plates being pushed around on top of a gelatin mantle (or close rheological equivalents).

After five days, my brain is definitely full. But I’m also really motivated to head back home, get what I presented this year written up and published, and get to work on new science to present next year. Lets hope my good intentions survive Christmas!

Anne: While the focus of AGU is surely the talks and posters, the biggest value is really the conversations that happen here. Whether they are in front of a poster, after a talk, over lunch or in the hallway, when you put more than 20,000 enthusiastic geoscientists together, lots of great ideas are sparked.

Chris: That’s a great summary, and a good place for Highly Allochthonous to bid adeiu to AGU 2011. We hope that our posts this week have given our readers some sense of why we came to San Francisco, and why we’ll probably keep coming back. It’s goodnight from her..

Anne:…and it’s goodnight from him.

Chris and Anne: Goodbye!

Chris: Wasn’t it the first of your two invited talks this morning? How did it go?

Anne: It went well. Even though I hadn’t managed to run through the presentation out loud beforehand, I hit the final slide with 20 seconds before the light came on, and a couple of people stuck around until after the session to ask questions and give feedback. Plus, the other talks in my session were really cool. I learned about catastrophic ecosystem shifts, landscape controls on net ecosystem productivity, a sedge that behaves like a boulder, and all sorts of neat connections between water, landforms, and life that I hadn’t known much about before.

What did you do this morning?

Chris: Good question. I started off this morning going to a workshop on NSF funding.

Anne: That sounds useful. Any pro tips?

Chris:It was more a good introduction to the complexities of the US funding system, but they did start off by trying to dispel pessimistic rumors about funding levels. The program officers all seem to think it’s a great time to get good geoscience done.

Later in the morning, I sat in a session on the challenges of interpreting rock magnetic records from sediment cores. It’s quite fast and easy to measure things like magnetic mineral concentration and grain size, which can theoretically act as proxies for environmental changes that effect sediment source and supply. Unfortunately, magnetic minerals also tend to be highly sensitive to redox conditions, which means that any environmental signal is convolved with a strong diagenetic filter that can drastically alter the original record. Most of the talks emphasised how difficult it can be to see through the effects of diagnenesis. However, the session ended on a positive note by introducing a potentially cool new source of high resolution magnetic records – from stalagmites in cave systems.

What did you move onto after your talk session concluded?

Anne:In a way I had a nice transition into thinking about my talk for Thursday. I ended up in the poster hall vortex, unexpectedly looking at volcano geomorphology posters. I watched Gordon Grant get very excited about critical flow in molten lava, and I was pleased to see Brian Romans’ fantastic picture of standing waves on the poster. Then I learned what happens when a pyroclastic density current falls off a cliff. After a working lunch, my brain needed a rest and found solace in the geomorphology corner of the exhibit hall, where within the space of a few short meters I found the Emriver stream table, the National Center for Earth Surface Dynamics delta model, and the St. Anthony Falls Lab high-resolution terrain scanner. After that I was ready to head back to talks, and a funny thing happened.

Chris: Oh? What’s that?

Anne: I ran into you.

Chris: Ah, yes. We both decided to attend the Birch Lecture, given by Michael Manga. I believe I was grumbling a bit after sitting through the latest episode of ‘nobody ever believes the paleomagnetists’ in the companion session to my poster session yesterday. Lots of presentations trying to understand the tectonic forces that caused the bend in the Hawaii-Emperor hotspot chain 50 million years ago, when the paleomagnetic data show clearly it’s more to do with the hotspot moving – or ceasing to move – than any change in the motion of the Pacific plate. We’ll convince them eventually – if you can get both of us attending the same talk at AGU, anything can happen.

Fortunately, I soon got into Michael Manga’s very interesting discussion of the hydrological effects of distant earthquakes. It was actually rather impressive seeing how the transient stress produced by the passage of seismic waves could produce large and permanent changes in groundwater flow. It certainly provides some insight into how similar changes, deeper underground, could affect volcanic and earthquake activity.

Anne: [Evil laughter] I knew I’d corrupt you eventually. It’ll be groundwater flow modeling for you next! The earthquake hydrology stuff was quite interesting, but I know the big draw of that talk was Manga’s work on Lusi, the Indonesia mud volcano. Maybe there will be an update on his latest calculations, and what Lusi is doing lately, on this blog at some point?

Chris: I did find it a rather ironic counterpoint that his work on Lusi is all about disproving an earthquake connection – which he did, fairly convincingly. As for an update post, we’ll have to see; he did point to some newly published calculations on the potential longevity of Lusi’s eruption (there’s a 50% chance it will continue for another 50 years) which may be worth looking into.

But first, I have to survive the rest of the conference.

Anne: At least you don’t have to give another talk tomorrow morning.

Chris: True enough. Good luck!

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Anne: So, Chris – how did your poster session go?

Chris: It went pretty well. The two key things that you want from a poster session are that you spend more time talking to people than you do standing and staring hopefully at everyone wandering past, and that the people you talk to don’t find glaring, basic flaws in the scientific story that you’re trying to present. Most people seemed to think that I had an interesting story about global ridge motions and how the EPR is fixed in the mantle, and I still had my voice at the end of it all. So I’m pretty satisfied.

Chris discusses his poster. Camera angle cunningly chosen to hide confused look on the face of his audience.

Anne: And did you get to those talks you wanted to see this afternoon during your poster session?

Chris: I got to the Gutenburg Lecture just after lunch. Thorne Lay gave a great overview of how seismic and geodetic data from continuous GPS receivers are being combined to great effect in studies of large subduction zone earthquakes, like the 2004 Sumatra earthquake and this years Tohuku earthquake off Japan (what he called ‘seismo-geodesy’). It was quite fun for me because a lot of the earthquakes he talked about were quite familiar to me through my blogging about them.

Sadly, a lengthy discussion at my poster prevented me from attending the rock magnetism talk I was planning to go to at the end of the day. By the time I’d finished talking, the lecture had already been going for 15 minutes.

Anne: Yeah, I know what you mean. I missed a whole hour of talks I meant to see, but had really good, useful conversations in that time instead. I’m starting to think that the poster hall has a serious gravity well associated with it. Every time I think I’m going to escape its orbit and go and listen to some talks in Moscone West, I get sucked back into the vortex by just one more interesting poster, or an encounter with a long-time acquaintance.

Chris: So any highlights from the poster hall vortex?

Anne: I had a couple of really good discussions about linking topographic form of watersheds to the geomorphic processes that shape them, which is directly related to the talk I’m giving tomorrow morning, so it was helpful to see what other people were thinking and doing in places ranging from endorheic basins in Chile to the mountains of Idaho.

But the definite highlight of my time in the poster vortex was running into a former undergraduate student of mine, who took my very first offering of hydrogeology. Now he’s completing a Masters degree in hydrogeology.

Chris: Very cool. My adventures in the vortex centered around the tectonics of subduction zones – particularly what happens when you try to subduct things like ridges and seamounts. I also had a good discussion of new data being collected along the Hikurangi subduction zone off New Zealand, which is a long-standing interest from my PhD research. But I did finally escape to Moscone West, where I sat in on an interesting series of talks about the role of tectonic inheritance in determining the structure of mountain belts. I’d never really appreciated this before, but if a continental collision is the end result of an ocean basin closing, then that ocean had to have first opened up by rifting; and it seems that the structures that formed during that rifting are very important when you get to the mountain building stage. So to truly understand mountain belts, you have to think quite long-term.

And you managed to escape to see some talks today, didn’t you?

Anne: Yes. I spent a good chunk of the afternoon in a hydrology session on ‘Landscape system response under change’, which had talks on the intersections between hydrology, geomorphology and biology. I especially liked Ellen Whol’s talk on the influence that headwater stream geomorphology plays on carbon storage in coarse wood in the floodplain and channel and in fine sediment. Beavers may play an important role in the carbon cycle!! It got me wondering about ways that urban stream hydrology and geomorphology may influence carbon dynamics.

Actually, Chris, it was all about allochthonous materials – at least as I understand them!

Chris: Well, there’s at least one word I understand! Once again, we both had very busy days which had very little in common with each other. It just goes to show just how much is going on at AGU. Bring on Wednesday!

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Chris: So how was your first day at AGU? You had a poster to present this morning, I think.

Anne: It wasn’t really my first day, you know. Yesterday I was at the Berkeley Catchment Science Symposium which was filled with really great talks on topics ranging from floods to metal isotopes, and lots of great discussions. It was a great way to get my head into the intense science week of AGU.

Chris: Alright, I’m a slacker.

Anne: But, yes, the poster. I was standing in for my graduate student Alea Tuttle and colleague Sara McMillan, who were unable to make it to the meeting. The poster presents some cool data on how stream restoration affects nitrogen dynamics at the stream-reach and individual structure scale. Alea did a great job putting the poster together so that it was very clear what she’d done and found, but I did get a few questions I wasn’t fully able to answer, so I’ll be going back to Charlotte with a few queries for Alea. I’m sure they are all things she’s thought of, and I’ll get a chance to learn some more nitrogen stuff as she explains things to me.

Chris: Excellent. What did you get up to when you weren’t manning your poster?

Anne: I saw a few talks – also on nitrogen, as it relates to hydrologic dynamics. And I caught up with old friends and made some new ones. After going to AGU for about 6 years, it’s amazing how much of a community it becomes.

How about you? You weren’t still working on a presentation, were you?

Chris: I got my poster done before getting on the plane, thank you very much. I’m presenting it tomorrow afternoon.

Anne: So, plenty of time to learn about interesting new science, then.

Chris: Yep. I ended up spending a lot of time today listening to talks discussing the interactions between convection in the mantle, plate tectonics, and topography – an area that my current research semi-overlaps with. I found it quite interesting how, depending on the research objectives, some people were using plate motions to drive mantle convection models, whereas other people were using the history of subduction encoded in the mantle’s temperature structure to refine plate motions. Several talks also emphasised how important mantle flow in response to subduction is in determining things like slab dip and deformation on the overiding plate.

In between talks, I visited the poster hall to look at the paleomagnetism contributions – experimental dynamos, Pangea reconstructions, the timing of the India-Asian collision, oh my! There were also a few interesting ones on dynamic stress triggering following large earthquakes – including a study that proposed that surface waves from a large main shock could circle the globe and trigger its own aftershocks. This falls into the ‘too cool not to be true’ category, although statistically it’s not quite a slam dunk yet,

Anne: Wow, that is cool. But are you sure we’re attending the same conference?

Chris: Well, we both turned up at the same Social Media Soiree.

Anne: Purely coincidence, I’m sure…

Chris: Maybe the next few days will expose some topics of converging interest for the Highly Allochthonous bloggers.

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