with Peter Kelemen
Originally presented 10 Mar 2007
Feedback in Geological Processes: What Instability Can Do for You!
Peter Kelemen writes:
I will cover the rudiments of some feedback processes in geology, focusing mainly on things that I have studied in my own research. We will just skate over the surface, to develop an intuitive feeling for the factors that lead to positive feedback, and thus create geological structure even when things start from a random state.
We will talk about “reactive porous flow”, in which a liquid solvent (like water) passes through a partially soluble porous matrix (like a mixture of salt and glass balls). In this kind of process, long fingers – dissolution channels – form along the direction of liquid flow. This happens because dissolution of salt makes more pore space, which in turn allows fresh water to flow faster in some places compared to others. This feedback between dissolution and water flow causes an “instability”, leading to exponentially growing channels with predictable shapes. Such a process is important in transporting lava from the Earth’s interior toward the surface. Magma literally dissolves channels that permit faster, coalescing flow.
A very similar process forms erosional channels, for example channels that form on beaches at low tide, when the groundwater comes out onto the beach surface. These erosional processes form coalescing networks where many small channels, all active at once, feed a few smaller ones. This leads to a “fractal” structure, in which the log of channel size is inversely related to the log of the number of channels of that size. I will make sure that participants leave with a good, intuitive understanding of how this happens. No math.
Depositional processes, during reactive porous flow and sediment transport, produce downward divergence of channels, for example forming wide deltas where rivers begin to deposit sediment. However, this is not completely symmetrical compared to erosion. In depositional networks, often only one or two channels are active at a time, with flow jumping suddenly from old to new channels. This can give rise to very periodic behavior, for example periodic volcanic eruptions from a single volcano, and periodic spacing of volcanic vents along a rift zone.
Earthquakes may arise from another type of periodic feedback process, in which gradual elastic loading leads to sudden brittle or viscous failure. I’ve been studying a potential, new earthquake mechanism involving “frictional” heating; the strength of many materials decreases exponentially with increasing temperature. In a narrow shear zone under stress, slow sliding leads to heating, which dramatically weakens the material, increasing the sliding rate, and in turn increasing the heating rate. Again, this positive feedback leads to an instability – in the end, parts of the shear zone melt very suddenly and an earthquake results from this sudden weakening. One such mechanism generally produces perfectly periodic cycles of loading and stress release. OK, then it should be easy to predict earthquakes, right? Well … maybe. However, coupling several shear zones separated by elastic layers can make the period highly irregular, even “chaotic”, in the same way that coupling two pendulums can have take unpredictable swings. Still, if one pendulum is bigger than the other, the period of the big one is pretty steady. This might hold for earthquakes as well … if the period is longer than historical records – hundreds of years in North America, thousands in Eurasia – we will have to wait to find out! Alternatively, perhaps scientists working together can come up with a good, predictive theory.
Building on intuition gained from studies of melt transport, erosion and earthquakes, my colleagues and I have been thinking about feedback processes in forming solid carbonate minerals from CO2 in the air and ocean. As many participants will know, industrial input of CO2 has increased atmospheric CO2 concentrations dramatically in the last 100 years or so, and this process has also affected the oceans. Scientists suggest that high atmospheric CO2, in turn, is contributing to global surface temperature increase, rising sea level, and melting ice caps. Most specialists agree on this. As a result, it would be good to develop a method for taking atmospheric and oceanic CO2 and “sequestering” it in solid calcium and magnesium carbonate minerals that are stable over very long periods of time. Most known processes for carbon sequestration are expensive because they require human intervention in the form of capturing CO2, transporting it, pumping it into the sub-surface, heating reactants, and/or grinding and preparing reactants rich in calcium and magnesium. We are hoping that, instead, we can learn from hot springs, on the surface and beneath the ocean, that form large volumes of carbonate naturally. Many participants will have seen travertine terraces in Yellowstone National Park, and some will have seen the huge carbonate chimneys on the seafloor in the recent IMAX movie, “Aliens of the Deep.” We think that the process involved in carbonate deposition in these springs can involve positive feedback – temperature and volume changes driven by the chemical reactions that form carbonate and associated minerals may heat the rocks and form fractures, in turn increasing reaction rates and the flux of water through source rocks rich in calcium and magnesium. If we could “jump start” this natural feedback process on a large scale, it could provide an economical alternative to more industrial carbon sequestration processes.
Introduction to this Workshop
Here is the introductory slide show presented by Dr. Passow.
Click on your preferred format: ppt or htm
Other E2C Workshops that have dealt with the concept of flow in systems:
“Soluble Salts of the Earth” with David Walker (Oct 2001)
“Arsenic in the Groundwater of Bangladesh” with Lex Van Geen (May 2003)
“The Plumeflow Project” with Martin Stute (Jan 2005)
Cutting-Edge Research
From Dr. Peter Kelemen’s LDEO web page:
Fields of Interest: Melting and melt transport in the Earth’s mantle; igneous processes in forming the Earth’s crust; ductile deformation and evolution of the lower crust.
My primary research interest is in the genesis and evolution of the Earth’s crust in the ocean basins, in arcs, and in continents. I approach this topic from the perspective that reactions between melt and rock during transport through the upper mantle are as important as melting, mixing, and crystal fractionation processes in producing different crustal bulk compositions in different tectonic settings. Thus, in an ongoing effort, I’ve tried to develop a general theory that explains how reactive melt transport varies along different geothermal gradients, with, 1. mineral dissolution and focusing of flow into high permeability channels in hot, upwelling mantle, 2. diffuse flow where there is a low melt flux into conductively cooled, shallow mantle, and, 3. hydrofracture where high melt flux and crystallization due to cooling clog porosity, leading to ponding of magma and increasing melt pressure.
Over the years, I have become increasingly fascinated with pattern formation during fluid transport processes, and I hope to generalize some of the lessons learned to hydrology and to erosion processes on the Earth’s surface. I’ve been very fortunate to work with a large number of tolerant geophysicists (Jack Whitehead, Einat Aharonov, Steve Holbrook, Marc Spiegelman, Greg Hirth, Jun Korenaga, Matthew Jull, and others) who have led me into the world of geodynamics. I am grateful to them all, particularly Greg Hirth with whom I have been able to pursue interdisciplinary studies of melt transport in the upper mantle and lower crust beneath oceanic spreading ridges, igneous accretion, thermal history, and composition of the oceanic lower crust, Tertiary magmatism in East Greenland and hotspot magmatism worldwide, genesis of the cratonic upper mantle, and arc magmatism and continental genesis.
Finally, not that long ago, I was a founding partner of Dihedral Exploration, mineral exploration consultants specializing in field work requiring technical climbing skills. Searching for ore deposits took me to British Columbia, Alaska and Greenland. I’d be happy to resume working on ore deposit geology with interested students.
Link to “Compaction Reaction” papers and movies by Marc Spiegelman and others, including Peter Kelemen.
Integrating Educational Technologies into Your Classrooms
Utilizing the power of educational technologies has become more vital with each passing year. One of the leaders in the field of integrating technology into education is Dr. Cristiana Assumpção, co-founder of the online Earth2Class Workshops for Teachers, and Educational Technology Coordinator at COLÉGIO BANDEIRANTES in São Paulo, Brasil. Dr. Assumpção earned her doctorate from Teachers College, Columbia University, in Instructional Technology and Media (2002.) Below on this page, she shares some of the information she uses in her teacher enhancement programs offered through her school and elsewhere in Brasil.
Note: Many of the following links are hosted on external websites and may have been altered or closed by the creators. Please notify us if you find this to be the case–michael@earth2class.org.
Each E2C session provides an opportunity for teachers to explore different aspects of educational technology, and then share what they do with others.Here are links to these:
Using “GeoMapApp and Google Earth” (with Andrew Goodwillie and Steve Kluge)
Using the Global Climate Change Project (with Mark Becker)
Using Graphic Novels in Your Curriculum (with Carl Brenner)
Using Movies Effectively in Your Classroom
Using Social Media for Your Curriculum
Using Featured Films with Your Class
Suggestions from Cristiana Assumpção:
Notes from 60-hour Professional Development Course on Educational Technology
(Log-in as “Guest”)
Tips on How to Manage Collaborative Group Work in the Classroom
Using Digital Cameras in the Classroom
Using “The Monster Project” in Your Classroom
Electronic Teacher-Student Communication Strategies
Using Online Interactive Strategies
Filamentality
PowerPoint Games
Templates for Creating PowerPoint Games
Prezi
Size and Scale in the Universe — Nicole Sonoski, Southside HS
Reducing Image Sizes
SUGGESTIONS FOR USING GOOGLE EARTH — Steve Kluge
Viewing Google Earth Files
DLESE NY Landscape Regions in Google Earth
About the DLESE NY Landscape Regions In Google Earth Project
SELECTED SUGGESTIONS BY OTHER EDUCATORS:
Locating Third-Party PowerPoints
Suggestions from Brian Hugick (Somers H.S.)
Creating “Hangman” Games for Students
Suggestions from Charles Burrows (Spring Valley H.S.)
Creating Podcasts
Suggestions from Michael Breed (Chenango Valley HS, NY)
Let’s Get Down to Earth … Science (Podcast lessons by Michael Breed)
Favorite apps
Web Quests
A Complete Guide to Creating Web Quests (suggested by Anne Hughes, Monument Charter School)
Turning Students into Strategic Researchers: Web Scavenger Hunts (Suggested by Ruth Clark)
Education Multimedia Visualization Center (Suggested by Ijaz Akhtar, Science Teacher
Theater Arts Production Company School): http://emvc.geol.ucsb.edu/downloads.php
Marco Polo — Internet Content for the Classroom
SERC (Science Education Resource Center at Carleton College):
“On the Cutting Edge: Professional Development for Geoscience Faculty.”
Of particular interest:
Teaching Geoscience with Visualizations
Developing Effective Online Educational Resources in the Geosciences
Teachers’ Domain Multimedia resources for the Classroom and professional Development:
http://www.teachersdomain.org/
TERC HANDS-ON: A publication for mathematics and science educators (Fall/Winter 2003, v. 26, no. 2)
“Teachers as Educational Designers” http://esbd.terc.edu/homepage/esbd_article.pdf
“Seven Deadly Sins of Power Point Presentations” from Dr. Joseph Sommerville
http://entrepreneurs.about.com/cs/marketing/a/7sinsofppt.htm
“ES Videos” by Rod Benson, Helena (MT) High School
I have recently posted several Earth Science-related videos on the Teacher
Tube web site. The videos, which show demonstrations and activities, are
each about 3 minutes long. The titles are listed below.
To view the videos, go to www.teachertube.com and then enter “Rod Benson”
into the search box. You will also find information about how to access
student handouts, answer keys, etc.
Multimedia
Images from this Workshop (courtesy of Greg Hofer)
Link to “Compaction Reaction” papers and movies
by Marc Spiegelman and others, including Peter Kelemen.