New sonar data from around Anak Kratatau constrain size of December 2018 collapse

Posted on December 16, 2019 by Chris Rowan

BBC story here. These data indicate a smaller collapse, but also a shallower failure plane than expected, which allowed that smaller volume to still generate a devastating tsunami.

Basically, when modelling this, different combinations of slide volume and failure angle can produce the same size of tsunami: less rock spending more time moving through shallow water can generate as big a tsunami as more rock spending less time doing so. This is an example of what in geophysics we call the ‘inverse problem’: there are many possible ways of interpreting the incomplete (and often indirect) measurements of the thing we are trying to understand, all of which reasonably ‘fit’ the data we have.

We can use our geological knowledge of how the Earth generally behaves, or how we’ve seen specific systems like this behave in the past, to rule out some possibilities, but often – as in this case – the only way to further zero in on the real solution is more data.

The important point here is that smaller landslides tend to occur more often than big ones, which increases the potential tsunami hazard posed by collapses of Anak Krakatau and other volcanoes like it.

Categories: geohazards, geophysics, volcanoes

Oxygenation of Earth’s atmosphere may not have required a trigger event after all

Posted on December 14, 2019 by Chris Rowan

In Earth history, there have been 3 abrupt jumps in atmospheric oxygen. A evolutionary or tectonic trigger is usually invoked, but a new study just published in Science suggests all you need is gradual oxidation of earth’s surface plus feedbacks within & between the P(hosporous), C(arbon) and O(xygen) cycles.

A timely reminder that the Earth system is complex and full of non-linear responses to anything which prods it. Any change doesn’t just depend on the size of the prod, but also the state of the planet when it is being prodded. Kicking a pebble in a valley and kicking one on a steep scree slope can lead to very different results! Or more accurately in this case, you can slowly add dozens of pebbles to a pile and nothing happens – until you add the last one that collapses the whole thing.

If you ever hear about climate ‘tipping points’, this is what is meant: we may get to where the accumulated changes that our civilisation is imposing on the Earth system push it into a state where even a small further push is like the final pebble on the pile.

If you ever hear about climate ‘tipping points’, this is what is meant: we may get to where the accumulated prods that our civilisation is making on the Earth system push it into a state where even a small further prod is like the final pebble on the pile. Most importantly, once the threshold is crossed, and non-linear changes have started cascading through the system, we are all along for the ride.

https://www.youtube.com/watch?v=60loeoblu0M
Categories: Archean, climate science, deep time, geochemistry, geology, Palaeozoic, past worlds, Proterozoic, society

How long was the last magnetic reversal – and why might subducting slabs have had a say in what it looked like?

Posted on August 14, 2019 by Chris Rowan

A new paper on the chronology of the last magnetic reversal concludes it took 20,000 yrs, and there were two distinct excursions – where the field becomes weak and disorganized, but it recovers without reversing polarity – before the main event about 773,000 yrs ago.

The paper combines magnetic records from igneous and sedimentary rocks, which have different strengths and weaknesses:

  • Cooling volcanic lavas take accurate spot readings of the magnetic field, but you only get a reading when there is an eruption. Your spot readings are…spotty!
  • Marine sediments can preserve an almost continuous record, but even at relatively high rates of deposition it is smeared out by bioturbation, so you are averaging the field direction over a 1000 years or more. That can average out a lot of variation, even in ‘normal times’!

The proposed duration of the reversal period is longer than most recent suggestions I’m seen (which are more of the order of 6000–10,000 years). The actual final reversal interval is more in line with this – it is just (in this account) preceded by a longer period of unrest.

See also the excellent write-up of this paper by Scott Johnson at Ars Technica. It is important to note that events like this are really pushing at the resolution limits of geological records, so getting a coherent and reliable picture is very tough.

The above study briefly discussed the fact that although the field during a reversal is non-dipolar, weak and disorganised, the places that rocks formed during these transitional periods think the magnetic poles is appear to fall in preferred longitudinal bands. Basically, the tiny rock magnets that record the field direction during reversals point more often than not point towards ‘north poles’ on arcs that run through the Americas and the W Pacific/Australia.

Map of the world centred on the Pacific Ocean. Colored lines with dots depict the migration of the magnetic pole as seen by rock units formed during the last field reversal.
‘Virtual Geomagnetic Poles’ in lavas spanning the last magnetic reversal, showing transition from reversed to normal polarity along two bands around the edges of the Pacific. Source Singer et al., 2019.

There is a lot of debate over whether this apparent preference exists at all, or is just a sampling artifact (remember, our recording medium – rocks – does not really have the resolving power to properly ‘see’ a reversal). If it does exist, there is also a lot of debate over the mechanism. Which brings me to another recent paper on this very subject, which rather blew my mind.

It reports high pressure experiments that indicate hematite in subducting slabs, formed from low temperature alteration of magnetite at the surface or decomposition of magnetite during subduction, might remain ferromagnetic (able to retain a strong remanent or permanent magnetisation) down to around 600 km depth.

So in places like the Western Pacific, where subduction has been going on for tens of millions of years, there might not just be a large slabs of cold rock hanging around in the upper mantle, but large magnetic slabs of cold rock. Currently, the magnetism of these subducted slabs is not particularly strong compared to the main (core) field of the Earth. But when that field is weak, where might your compass end up pointing? Maybe the big mass of magnetic rock in the upper mantle?

Map of the world centred on the Pacific, with red dots showing position of magnetic pole as it migrated between geographic poles during multiple field reversals. In the western Pacific, the red dots overlap with the inferred position of subducted and magnetic oceanic lithosphere, shown in blue.
Blue region: position of subducted lithosphere in Western Pacific at mantle depths of 500km. Red dots: ‘virtual geomagnetic poles’ from multiple reversals, including the last one. Source: Kupenko et al., 2019.

Although the authors focus on the Pacific, there are also significant subducted slabs beneath North America (the Farallon slab) and South America, which could play a similar role. Is this correct? Who knows at the moment? But it’s a truly intriguing idea that took my breath away when I read it.

[This post was collated from two twitter threads: here and here]

Categories: geology, palaeomagic, paper reviews, rocks & minerals

Whet your Appetite with these 45+ Books on Water

Posted on March 3, 2019 by Anne Jefferson

A post by Anne JeffersonFor some reason, I have a lot of books about water on my shelves. But my collection, seems like a drop in the ocean (forgive me) compared to all of the great books on water that are out there.  I love the number of different ways that people write about water – from broad historical overviews to sharp-eyed analyses of current water resource challenges or lyrical explorations of the waters of a region. Often a single book will examine the topic from more than perspective, revealing how integral and integrated water is with past, present, and future and both natural ecosystems and human societies.

I’ve attempted to take an inventory of the water books for the popular press, published in English over the past two decades or so, divided into very rough categories.  I’m sharing the list with my Watershed Hydrology students in the hopes that they explore the ways that the technical topics we cover in class have broader connections. But having compiled the list, I thought I’d put it here in case you are looking for a good book to read, in which case…dive in.

Water Resources (general/American perspective)
  1. Blue Revolution: Unmaking America’s Water Crisis by Cynthia Barnett*
  2. Elixir: A History of Water and Humankind by Brian Fagan*
  3. Big Thirst: The Secret Life and Turbulent Future of Water by Charles Fishman
  4. Your Water Footprint: The Shocking Facts about How Much Water We Use to Make Everyday Products by Stephen Leahy
  5. Water: A Natural History by Alice Outwater
  6. Replenish: The Virtuous Cycle of Water and Prosperity by Sandra Postel
  7. The Ripple Effect: The Fate of Fresh Water in the Twenty-First Century by Alex Prud’homme
  8. Water 4.0: The Past, Present, and Future of the World’s Most Vital Resource by David Sedlak*
  9. Water: The Epic Struggle for Wealth, Power, and Civilization by Steven Solomon
  10. see also all other headings
International Perspectives on Water
  1. Blue Covenant: The Global Water Crisis and the Coming Battle for the Right to Water by Maude Barlow
  2. Whose Water is It? The Unquenchable Thirst of a Water-hungry World by  Bernadette McDonald and Douglas Jehl
  3. Water Wars: Drought, Flood, Folly, and the Politics of Thirst by Diane Raines Ward
  4. Water Wars: Privatization, Pollution and Profit by Vandana Shiva
  5. Let There Be Water: Israel’s Solution for a Water-Starved World by Seth Siegel
Rain
  1. Rain: A Natural and Cultural History by Cynthia Barnett*
Lakes and Wetlands
  1. Still Waters: the Secret World of Lakes by Curt Stager
  2. Mirage: Florida and the Vanishing Waters of the Eastern US by Cynthia Barnett
  3. See also the Laurentian Great Lakes
Rivers
  1. The Source: How Rivers Made America and America Remade it’s Rivers by Martin Doyle*
  2. When the Rivers Run Dry: Water – the Defining Crisis of the 21st Century by Fred Pearce
  3. See also The American West and Terrible Floods
Groundwater
  1. Water Follies: Groundwater Pumping and the Fate of America’s Fresh Waters by Robert Glennon*
Drinking Water
  1. Blue Gold: The Fight to Stop the Corporate Theft of the World’s Water by Maude Barlow and Tony Clarke
  2. The Poisoned City: Flint’s Water and the American Urban Tragedy by Anna Clark
  3. Drinking Water: A History by James Salzman
Water in The American West
  1. Cataclysms on the Columbia: The Great Missoula Floods by John Elliot Allen, Marjorie Burns, and Scott Burns
  2. Emerald Mile: The Epic Story of the Fastest Ride in History through the Heart of the Grand Canyon by Kevin Fedarko*
  3. Water is For Fighting Over: and Other Myths about Water in the West by John Fleck*
  4. A River Lost: The Life and Death of the Columbia by Blaine Harden
  5. The West Without Water: What Past Floods, Droughts, and Other Climatic Clues Tell Us About Tomorrow by B. Lynn Ingram and Frances Malamud-Roam*
  6. Water and Power: The Conflict over Los Angeles Water Supply and the Owens Valley by William Kahrl*
  7. Sustainable Water: Challenges and Solutions from California by Allison Lassiter
  8. River of Renewal: Myth and History in the Klamath Basin by Stephen Most
  9. Where the Water Goes: Life and Death Along the Colorado River by David Owen
  10. Dead Pool: Lake Powell, Global Warming, and the Future of Water in the West by James Powell
  11. Cadillac Desert by Marc Reisner*
  12. Rivers of Empire: Water, Aridity, and the Growth of the American West by Donald Worster
The Laurentian Great Lakes
  1. The Great Lakes Water Wars by Peter Annin*
  2. The Death and Life of the Great Lakes by Dan Egan*
  3. The Living Great Lakes: Searching for the Heart of the Inland Seas by Jerry Dennis
  4. Sustaining Lake Superior: An Extraordinary Lake in a Changing World by Nancy Langston
Terrible Floods
  1. Rising Tide: The Great Mississippi Flood of 1927 and How it Changed America by John Barry*
  2. The Johnstown Flood by David McCullough*
Water and Living Things
  1. Eager: The Surprising Secret Life of Beavers and Why They Matter by Ben Goldfarb
  2. King of Fish: The Thousand Year Run of Salmon by David Montgomery
  3. KIngs of the Yukon: One Summer Paddling Across the Far North by Adam Weymouth
Science of Water
  1. The Water Book: The Extraordinary Story of Our Most Ordinary Substance by Alok Jha*
No links here, because you should look for these books at your local public or university library, your locally-owned bookseller, or the retailer of your choice.
Did I miss a book you like? Let me know in the comments

*On Anne’s bookshelves.

Categories: geology

Some thoughts on #WomenInScienceDay

Posted on February 11, 2019 by Anne Jefferson

Today is the International Day of Women and Girls in Science. This day is designated by the UN because “Over the past 15 years, the global community has made a lot of effort in inspiring and engaging women and girls in science. Yet women and girls continue to be excluded from participating fully in science. At present, less than 30 per cent of researchers worldwide are women. According to UNESCO data (2014 – 2016), only around 30 per cent of all female students select STEM-related fields in higher education.”

As a woman in science, I’m grateful for the opportunities I’ve had to explore my interests, learn new concepts and skills, conduct research, and further my professional career. And I’m incredibly grateful for all of the wonderful women colleagues I have online, at my institution, and with whom I get to collaborate. So today is a day to celebrate what we have achieved for women in science. But it’s also a day to remind ourselves where we need to go.

Science is better when it is more diverse and inclusive, and gender is one important dimension of diversity. Check out https://undsci.berkeley.edu/article/socialsideofscience_02 for just a few of the reasons diversity improves science.

It’s also fundamentally right that folks with all genders have the same opportunities to study science and pursue science careers. Even if it didn’t make the science better (it does), diversity in would be a good thing. Because the opportunity to study and do science enriches the lives of those that are drawn to it.

I’m incredibly fortunate to have a trail-blazing scientist for my mother and I’ve benefited tremendously from the work that she and others of her generation did to diversify science. I hope I’m paying that forward to the next generation.

One of the ways that we can make science and society better is by paying attention to those who are multiply minoritized in science and the struggles and barriers that they face – and then working to remove those those barriers.

When we focus on gender as the primary axis of diversity, we help white women (like me) most. And while white women still face a lot of barriers to science careers (e.g., sexual harassment), we have it easy compared to women of color, women with disabilities, etc. (As evidence, women now earn 45% of geosciences doctorates in the US. But, it was 88% white people among those geosciences doctorates i earned by US citizens and permanent residents. The geosciences is whiter than any other science discipline. (Stats from here.))

Fortunately, there are a lot of minoritized women in science who are speaking up about their experiences and their recommendations to make science a more inclusive space. We need to listen to the voices of women like Dr. Chanda Prescod-Weinstein, Dr. Kat Milligan-Myrhe, Dr. Katherine Crocker, PhD student Itati SantaMaria de Chavez y Vasquez, undergraduate Elizabeth Gutiérrez, Ruth H Hopkins, Dr. Tressie McMillan Cottom, and so many more. We also need to listen to and support groups like the International Association for Geoscience Diversity and Latinas in Geoscience. But we can’t just listen, we need to grapple with why what they say makes us feel uncomfortable, and then we need to follow their advice.

In science, and especially in the geosciences, we have a long way to go to make our spaces truly inclusive for all people. Let’s use International Day of Women and Girls in Science to remind ourselves to get to work.


Even the UN needs a little help, having released a graphic showing 5 white women scientists. Twitter promptly came to rescue and this version is a much better depiction of the science we want. A later version include PPE on the scientists, and I suggested that we could do with more types of science represented as well. We don’t all work in a lab with white coats on.

#WomenInScienceDay

(adapted from a tweet thread, original here).

Categories: by Anne, general science