DEPARTMENT OF EARTH, ATMOSPHERIC, AND PLANETARY SCIENCES
Research and education within the Department of Earth, Atmospheric and Planetary Sciences (EAPS) engage a broad array of scientific disciplines: geology, geophysics, geochemistry, physical and chemical oceanography, meteorology, atmospheric chemistry, and planetary sciences. Particular emphasis is placed on the study of the complex geosystems in the Earth's atmosphere, ocean, crust, and deep interior and the similar systems on other planets. The Department comprises 42 faculty, including one with a primary appointment in Civil and Environmental Engineering, 215 graduate and undergraduate students, and 97 permanent research staff, postdoctoral appointments and visiting scholars.
During the past academic year, 175 graduate students were registered in the Department (Course 12) and the MIT-Woods Hole Oceanographic Institution (WHOI) Joint Program (Course 12W). The EAPS graduate program currently focuses on the Ph.D. degree, which is the goal of over 90% of its graduate students. There is a growing need, however, for professionals trained at the master's level who can solve geoscience problems in a broad, systems-oriented context. In response to this need, EAPS has proposed a new degree, Master of Science in Geosystems, which was approved during this academic year by the Science Council, the Faculty Policy Committee, and the Committee on Graduate School Policy. Plans are underway to open the new program for matriculation in September, 1997. This S.M. degree is designed to appeal to students seeking careers in industry as professional geoscientists, as well as working professionals who wish to expand their knowledge and opportunities in geoscience. It will prepare students for scientific and management careers in the environmental, natural resources, and technical consulting industries by providing skills in computer simulation and modeling of complex natural systems, as well as in scientific inference based on field observations and numerical modeling.
A second initiative, the Graduate Program in Atmospheres, Oceans, and Climate, is also being developed. Climate problems and other issues related to global environmental change are notable for their scientific difficulty and societal importance. This program will take advantage of the breadth of EAPS faculty expertise in these areas. Elements of the new Ph.D. curriculum will be put in place next semester.
EAPS is continuing efforts to improve the quality and scope of its undergraduate program. The bachelor of science curriculum has been reorganized to include three areas of concentration: geoscience, physics of atmospheres and oceans, and planetary science and astronomy. Each concentration encompasses a set of required courses, a sequence of field and/or laboratory subjects, and independent study or thesis preparation. An undergraduate minor degree program has also been developed to complement degrees in other disciplines, providing a foundation for careers that incorporate areas of geoscience. The Department has expanded its Independent Activities Program (IAP), and EAPS now offers more IAP courses for credit than any other MIT department. The Department continues to increase its participation in freshman advising seminars: this past year, EAPS faculty advised approximately 10% of the freshman class. EAPS has maintained a strong Undergraduate Research Opportunities Program (UROP), despite changes in federal regulations that have increased the cost of UROPs to grants and contracts.
Three new faculty joined EAPS this year. Kelin Whipple, a geologist specializing in the study of surface processes, was appointed Assistant Professor in July, 1995. His experience encompasses field work, laboratory experimentation, and numerical modeling across a broad range of geomorphological, transport, and tectonic problems. Maria Zuber, a planetary scientist who specializes in the structure and dynamics of planetary lithospheres, was appointed as a full Professor in November. Among her many accomplishments, Dr. Zuber was a key participant in the Clementine mission, both during the data-collection phase and in the subsequent scientific analysis, and she obtained spectacular results that have revolutionized the thinking on lunar structure. Robert van der Hilst, a seismologist, came to the Department from the Australian National University as an Assistant Professor in January, 1996. His primary research accomplishments involve the application of seismic tomography to imaging various features in the Earth's interior, including subduction zones, where descending lithosphere plunges back into the mantle.
The highlight of an exciting year was the announcement that EAPS Professor Mario Molina and two other atmospheric chemists received the 1995 Nobel Prize in Chemistry for their pioneering work on the depletion of stratospheric ozone by man-made chlorofluorocarbons. Principal Research Scientist Heidi Hammel was awarded the 1996 Harold C. Urey Prize by the American Astronomical Society, given for outstanding research by a young planetary scientist, and she was also honored by the 1996 Spirit of American Women National Award for encouraging young women to follow nontraditional career paths. Professor Thomas Herring received the Bomford Prize from the International Association of Geodesy. Professor Thomas Jordan was elected as a member of the American Academy of Arts and Sciences, and Professor Fred Frey as a Fellow of the American Geophysical Union. Professor Maria Zuber received the NASA Exceptional Scientific Achievement Medal, Professor Clark Burchfiel the Career Achievement Award from the Geological Society of America, and Professor Nafi Toksöz the Distinguished Achievement Medal from the Colorado School of Mines. Professor Edward Lorenz received the Battan Author's Award from the Bedford Institute of Oceanography, Nova Scotia. Professor Richard Lindzen was selected as the fourth Bernhard Haurwitz Memorial Lecturer for 1996, and Professor Marcia McNutt as the Phi Beta Kappa Distinguished Lecturer for 1996-7. Professor Leigh Royden was elected Associate Chair of the MIT faculty, a position she will occupy through June, 1997. The International Astronomical Union named asteroids after three members of the Department, Dr. Heidi Hammel and Professors Tim Dowling and Chuck Counselman, in honor of their contributions to planetary science.
GEOLOGY AND GEOCHEMISTRY
Professor Samuel Bowring and graduate student Dave Hawkins have pioneered a technique for U-Pb dating of monazites that involves imaging the grains using backscattered energy to identify different growth zones, followed by microsampling and precise analysis. They have achieved a spatial resolution similar to the ion microprobe (20 microns) but with an order of magnitude better precision. This has allowed them to elucidate very complex histories (up to 20 million years) of both the prograde and retrograde paths in metamorphic rocks from a single grain. Professor Tim Grove and colleagues have been investigating the processes that led to melting in the Moon's interior and the production of lunar mare basalts. Magmas that are produced deep in the Moon's interior heat and selectively melt ilmenite as they rise through the shallow crust on their ascent to the Moon's surface. This work has resolved the question of the origin of an enigmatic lunar mare basalt type discovered twenty-five years ago. Professor Fred Frey in collaboration with Dr. N. Shimizu (Woods Hole Oceanographic Institution) are identifying melt-rock reactions that occur in the Earth's upper mantle. They find that a peridotite massif now exposed in northern Japan originally formed from partial melting processes occurring 109 years ago in the oceanic mantle. Professor Kip Hodges's work in the Annapurna Range of central Nepal has demonstrated a close relationship between thermal, deformational, and erosional processes in the development of the Himalayan orogenic system. Professors Leigh Royden and Clark Burchfiel are mapping in China along the eastern margin of the Tibetan plateau, where they are studying the history of deformation and uplift of the plateau. Together with Principal Research Scientist Robert King, they have established a Global Positioning System (GPS) network that covers most of the eastern margin of the plateau. Results to date show that crust of the eastern plateau has been thickened and elevated by shortening in the lower crust, a mechanism as yet unrecognized in other mountain belts. Professor Kelin Whipple is currently engaged in field studies (Sierra Nevada, Himalayas, and E. Tibet) and numerical modeling of river profiles and their response to tectonic uplift. He is also constructing a new flume in the Sediment Laboratory for experimental study of debris-flow hazards. Professor John Southard is modeling the transport and deposition of sediments in rivers and in the oceans.
Professor Chris Marone is investigating the mechanics of earthquakes and faulting and the frictional properties of rock using a combination of laboratory experiments, numerical modeling, and analysis of seismic data. Recent work by Marone's group includes modeling of earthquake nucleation to study the effect of inertia and laboratory measurements of the rate of frictional strengthening under seismogenic conditions. Professor Brian Evans and his students and colleagues are working on understanding the effect of deformation on permeability and transport properties in rocks; they have shown that tectonic processes in the upper levels of the crust can increase the permeability and electrical conductivity of an intact rock by a factor of two or more before mechanical failure occurs, but that the most dramatic changes in transport properties occur when the deformation mechanism changes from dominantly brittle behavior to plastic flow. Professor Rob van der Hilst and colleagues at the Australian National University completed a tomographic imaging study of the complex slab structure beneath Indonesia. This study provided more evidence for slab penetration into the lower mantle and revealed that the slab had broken off beneath Sumatra. Professor Marcia McNutt recently returned from a 50-day marine geophysical expedition to the southern Austral Islands in which she collected multichannel seismic reflection and refraction data, gravity data, swath bathymetry, and tons of rocks. The new data show that the Austral Islands are composed of three distinct volcanic chains, such that the stresses produced in the plate by each older chain determined the location and orientation of the next younger chain, casting doubt on the model that midplate volcanism requires deep-mantle plumes.
Professors Bradford Hager and Thomas Herring, Senior Research Scientist Peter Molnar, and Principal Research Scientist Robert Reilinger have used GPS measurements to determine that nearly half of the convergence between India and Eurasia occurs north of Tibet, across the Tien Shan Mountains of Central Asia; dividing the total observed shortening across the range by this rate suggests that rapid convergence resulted from forces associated with the uplift of Tibet ~10 Myr ago. Hager and colleagues have also modeled the coseismic displacements for the 1994 Northridge earthquake; they are more consistent with faults rooting in the ductile lower crust than with faults ramping up from a seismogenic detachment fault, suggesting that the seismic hazard for the Los Angeles basin has been overestimated. Working with the Mongols and Russians, Dr. Molnar has quantified slip along the rupture of the 1957 Gobi-Altay earthquake, the last event with a magnitude greater than 8 in a continental region. He has found that this rupture comprised a strike-slip event on one fault plus a thrust event on a nearby fault; this complex rupture thus serves as a prototype for the worst possible earthquake in southern California. Professor Herring has used very long baseline interferometry (VLBI) data to develop a geophysical model of the diurnal changes in the Earth's rotation due to the torques from the Sun, Moon, and planets. This model is being adopted by the International Earth Rotation Service for the analysis of astrometric, astronomical and geodetic data. Professor Daniel Rothman has used a combination of statistical analysis, physical arguments, and numerical simulation to determine the physical mechanisms of poorly understood geological processes ranging from landscape evolution to the formation of and flow through sedimentary rocks. The former studies have yielded new results on the initiation of drainage networks, while the latter have included the discovery of non-Gaussian velocity fluctuations in slow flow through complex structures.
Professor M. Nafi Toksöz, Director of the Earth Resources Laboratory, has initiated two new projects with the Idaho National Engineering Laboratory: a study of the spatial variability of earthquake ground motions, and the development of an ultra-long, multi-sensor borehole seismic array. Dr. Reilinger and Professor Toksöz are heading an international GPS project in the Eastern Mediterranean, which is providing quantitative constraints on models of continental rheology and dynamics in this zone of continental collision. They are also using GPS to map deformation along the San Andreas fault system in S. California and N. Mexico, providing tight constraints on fault slip rates for earthquake hazard studies. Professor F. Dale Morgan continued environmental geophysics work at the Oak Ridge National Laboratory, Otis Air Force Base, and the Army Proving Grounds in Yuma, Arizona. In the laboratory, he is studying the frequency dependence of seismic-electromagnetic coupling in sedimentary rocks. He has also produced a new electrochemical model for the inception and prediction of earthquakes. Principal Research Scientist Arthur Cheng and associates have developed methods of determining shear wave anisotropy using downhole logging tools for in situ stress estimation for tectonic and exploration purposes. Professor Jordan and his students have discovered a phase of slow, transient deformation that precedes, and presumably initiates, many large earthquakes on oceanic transform faults. They have also derived new models of the Earth's upper mantle that include better estimates of seismic anisotropy, and they have formulated stochastic models to explain this anisotropy in terms of small-scale heterogeneities in anisotropic, olivine-rich mantle rocks.
Professor Maria Zuber, in collaboration with Dr. David Smith of the Goddard Space Flight Center, published a re-analysis of spacecraft occultation data resulting in an improved shape of Mars. The results provide a new, important constraint on models of Mars's early evolution. Zuber's laser experiment was successfully launched on the Near Earth Rendezvous spacecraft in February, 1996, and will arrive at the asteroid 433 Eros in 1999, when it will collect topographic measurements of the asteroid for a year. Professor Jack Wisdom has focused his dynamical studies on the evolution of the Earth-Moon system. He has found that the Earth-Moon system passes through a strong orbital resonance early in its evolution which can drastically change the configuration of the system and the subsequent evolution. Professor Richard P. Binzel has utilized the Hubble Space Telescope to produce the first geologic map of the asteroid Vesta, revealing regions of ancient lava flows and deep impact basins. His ground-based telescopic work has revealed new sources for meteorites among asteroids whose orbits cross that of Earth. Professor James Elliot and colleagues observed a second stellar occultation by Triton from several sites. Comparing Triton's atmospheric pressure derived from these data with those from their previous occultation showed little if any change over the two-year interval, which indicates that Triton's surface has an unexpectedly high thermal inertia. Dr. Heidi B. Hammel, Principal Research Scientist, has analyzed Hubble Space Telescope imaging of Neptune to determine the longevity of large storm systems in the planet's atmosphere. She has also continued studies of Jupiter's atmosphere during its recovery from the collision of Comet Shoemaker-Levy 9, again using Hubble imaging. Professor Tim Dowling combined his measurements of wave speeds in Jupiter's atmosphere from the Shoemaker-Levy 9 impact with previous theoretical work to predict that the eastward jets on Jupiter should increase in strength by 50-100% underneath the cloud tops, and his results were substantiated by the Galileo Probe Doppler wind experiment in December, 1995. Professor Charles Counselman and his students developed a new method of determining position using radio signals from satellites that greatly improved the precision of airplane runway approaches in flight tests conducted by MIT Lincoln Laboratory.
Professor Jochem Marotzke combined historical observations with a general circulation model of the Indian Ocean and found surprisingly strong seasonal variability in the deep circulation and the poleward heat transfer. In collaboration with Professor Peter Stone, he found that Southern Hemisphere atmospheric moisture transports determine the strength of the North Atlantic thermohaline circulation, but that Northern Hemisphere moisture transports determine its stability. Professor Maureen Raymo was chief scientist of an international oceanographic expedition on the drill ship R/V Resolution. Leading a group of 26 scientists, she directed the recovery of nearly seven kilometers of sediment from the sea floor, which will allow marine scientists to study the record of rapid climate variability in the past. Professor Edward Boyle successfully recovered the longest piston core in the Atlantic Ocean. The 53-meter core is being studied to create a century-resolution record of marine climate variability during the past 180,000 years. Professor John Edmond continued field work in the Far East in Siberia. The Lower Lena and Yana rivers were sampled last summer. Great progress was made on the development of 129I, derived from nuclear reprocessor effluent, as an oceanographic biogeochemical tracer. Professor Carl Wunsch's group has begun to produce ocean circulation estimates based upon global general circulation models, satellite altimetry and ocean acoustic tomography. These results are a prototype for an eventual system permitting depiction of the three-dimensional ocean circulation on a week-by-week basis. Professor Paola Malanotte Rizzoli and collaborators have been modeling the ocean's circulation in different regions using data assimilation to improve the models. She is also investigating the physical/biological dynamics of the Eastern Mediterranean and the Black Sea ecosystems in the context of multinational collaborative programs. Professors Glen Flierl and John Marshall are modeling the physics and biology of the Southern Ocean. Work in Professor Flierl's laboratory has focused on the dynamics of the North Equatorial current and the Gulf Stream, and on turbulence and biological patchiness. In the past year much of the effort of Professor John Marshall and his collaborators has been devoted to the development of a state-of-the-art ocean circulation model designed to exploit the new generation of massively parallel computers. His studies of oceanic convection have culminated during this last year in the planning of a large multi-national sea-going experiment to observe convection in the Labrador Sea in the winter of 1996-97.
Professor Mario Molina and his students have developed a new laboratory technique to measure rate constants for chemical reactions under temperature and pressure conditions directly applicable to the lower stratosphere. This new approach overcomes some of the significant limitations of existing techniques, such as the need to operate at low pressures, or the occurrence of secondary reactions taking place at the walls of the flow reactor. Professor Ronald Prinn, in collaboration with colleagues in the Sloan School of Management, Center for Global Change Science, Department of Economics, and the Marine Biology Laboratory, developed and recently tested a unique Integrated Global System Model for climate policy analysis. This model addresses most of the major anthropogenic and natural processes involved in climate change. Professor Peter Stone and his colleagues have calculated the rate of heat uptake by the oceans in global warming experiments with the most advanced coupled atmosphere-ocean general circulation models. The results were highly model-dependent, and the range of values they found represent a new source of uncertainty in estimates of global warming. Professor Kerry Emanuel developed a general theory for velocity and buoyancy scales of moist convection and continued work on determining the control of atmospheric water vapor by cumulus convection. He developed a theory for hurricane eyewalls as examples of atmospheric fronts, and completed his analysis of field experimental data pertaining to tropical cyclogenesis. Professor Edmund Chang investigated the effects of tropical heating anomalies on the extra-tropical circulations. He found that poleward propagating perturbations are generated, which can be simply modeled as a delayed oscillator response of the mid-latitude jet to changes in the tropical circulations. The Galileo probe has found the slight positive static stabilities in the Jovian atmosphere that Professor Richard Lindzen and Petros Ioannou predicted were required for the tidal damping consistent with Io's orbit. Professor Lindzen has also initiated a program (in cooperation with NASA Goddard Space Flight Center) to look into the possibility of directly measuring climate sensitivity. Professor Reginald Newell's group participating in the NASA Pacific Exploratory Mission atmospheric sampling experiments in the west Pacific has discovered that tropospheric ozone and potential vorticity show a remarkable correlation for altitudes below 18 km. This work provides new insight into large-scale atmospheric transport processes, and assists in outlining regions where production and destruction of ozone by photochemical processes is important. Professor Alan Plumb's group has studied transport processes and rates in the stratosphere, through analysis of general circulation models and data obtained by satellite and by aircraft. During the past year, they provided meteorological support for the NASA-led VOTE/TOTE airborne experiment and are currently involved in the STRAT campaign.
Thomas H. Jordan
MIT Reports to the President 1995-96