Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2007. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 60-66). / Avulsions, or rapid changes in the location of a river, usually occur in environments such as deltas, floodplains, and alluvial fans where net-deposition can raise the bed of the river above its floodplain. Avulsions are less frequent in transient landscapes, such as New England, where topography and hydrography are still responding to recent glaciation. One of these rare avulsions occurred during a 100-year flood on the Suncook River, Epsom, NH, between May 14 and 15,2006. We studied the Suncook River event to develop a model for the drivers of avulsions in transient landscapes. We suggest that a strong substrate in the parent channel, such as bedrock or immobile boulders, can facilitate an avulsion by preventing incision and driving water overbank. Easily erodible substrates in the path of the new channel can also contribute to avulsions by allowing a knickpoint to migrate quickly upstream and create a channel with a more favorable slope during a single flood. Based on Slingerland and Smith's (2004) model, we also propose that a low water-surface slope in the parent channel could be a direct driver for avulsions. In the Suncook River, this low water-surface slope was created in the backwater of a small mill dam in the parent channel. A 200-year flood that occurred in the Suncook River in 1936 did not create an avulsion. We suggest that ice floats could have damaged the dam and increased the water-surface slope of the parent channel, making an avulsion less favorable and reducing the depth of water flowing overbank. The topography in the path of the 2006 avulsion, which was lowered by activity in a sand pit starting in the 1960s, probably prevented water from finding a new path. We believe that these anthropogenic modifications directly contributed to the occurrence of the May 2006 avulsion in the Suncook River. These conditions are common throughout New England, and could increase the risk of avulsions in the region. / by Mariela C. Perignon. / S.B.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Organic geochemistry provides researchers with an extensive suite of tools for reconstructing past environments. Using these tools, a set of unique locations situated in climatic extremes have been investigated. During the Early Cenozoic the planet was much warmer than today. In addition to this higher background temperature a series of rapid warming events occurred termed hyperthermals. The largest of these, the Paleocene-Eocene Thermal Maximum is perhaps the best analog to modern day anthropogenic climate change. It is paramount to understand the global effects of this event to elucidate potential changes in our near future. To further this area of research two very different regions were chosen to seek out potential deposits that record the hyperthermals. First, in the Cambay Basin of Western India an extensive core was taken during exploration for lignite deposits. This site would have been near the equator during the time of deposition, a region that is important yet not well established in the current literature pertaining to the hyperthermals. Biostratigraphy and palynology combined with bulk organic carbon isotope records reveals that the lowermost portion of the core likely contains the hyperthermal events. Compound-specific isotopic investigation across multiple realms reveals potential variability of carbon in the ocean-atmosphere system that was then complemented by examination of the corresponding kerogens through application of pyrolysis gas chromatography-mass spectrometry. Expanding upon this study the Canadian High Arctic was assessed in the form of paleosols from Banks Island and shales from Strathcona Fiord. Biomarker distributions revealed a shift in environmental conditions from marine to coastal environments from the Paleocene into the Eocene. Hydrogen isotopic investigation reveals that the nalkanes from paleosols can preserve the same signals as rocks from the same time and that the paleohydrology was far different from present day. Finally, a study was conducted of the recent history of Lagunas Miscanti and Miñiques due to their location at high elevations in the dry Chilean Altiplano. Examination of biomarker distribution as well as associated proxies shows that the lakes have undergone significant changes on centennial time scales along with varying biotic communities, water chemistry and lake level. / by Ross H. Williams. / Ph. D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2004. / Includes bibliographical references (leaves 48-49). / Trojan asteroids orbit the Sun at Jupiter's L4 and L5 stability points. They are included in the D-class group of asteroids because of their characteristically steep spectral slope. In accordance with spectra of other asteroid classes, we expected that the larger the diameter is of a D-class asteroid, the redder (visually) the asteroid should be in the visible spectrum. Approximately ninety Trojan asteroids have been examined, fourteen of which come from our own observations, and five of which are small and come from the SMASS I data set. The results did not confirm our original hypothesis. Instead, space weathering appears to affect Trojans in a different way than it does other asteroid classes due to their different composition. / by April A. Russell. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1989. / Vita. / Includes bibliographical references (leaves 94-101). / by Kelly Kenison Falkner. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2014. / 15 / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 50-51). / Abstract Errors in modeling atmospheric delays are one of the limiting factors in the accuracy of GPS position determination. In regions with uneven topography, atmospheric delay phenomena can be especially complicated. Current delay models used in analyzing GPS data from the Plate Boundary Observatory (PBO) are successful in achieving millimeter-level accuracy at most locations; however, at a subset of stations, the time series for position estimates contain an unusually large number of outliers. In many cases these outliers are oriented in the same direction. The stations which exhibit asymmetric outliers occur in various places across the PBO network, but they are especially numerous in California's Mammoth Lakes region, which served as a case study for this project. The phenomenon of skewed residuals was analyzed by removing secular trends and variations with periods longer than 75 days from the signal using a median filter. The skewness of the station position residuals was subsequently calculated in the north, east and up directions. In the cases examined, typical position outliers are 5-15 mm. In extreme cases, skewed position residuals, not related to snow on antennas, can be as large as 20 mm. I examined the causes of the skewness through site-by-site comparisons with topographic data and various forms of weather data such as numerical weather models, radiosondes, and satellite images. Analysis suggests that the direction of the skewness is generally parallel to the local topographic gradient at a scale of several kilometers. Comparison with weather data suggests that outlier data points in the Mammoth Lakes region occur when lee waves are likely to form downstream of the Sierra Nevada Mountains. The results imply that coupling between the atmosphere and local topography, e.g. lee waves, is responsible for the phenomenon of skewed residuals. / by Kathryn Materna. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1985. / Microfiche copy available in Archives and Science. / Bibliography: leaves 315-317. / by Melinda Darby Dyar. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2008. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 63-67). / Many studies have investigated tropical data assimilation in the context of global models or specifically for tropical cyclones, but relatively few have focused on the mesoscale predictability and observability of the general tropical environment. This work constructs an ensemble data assimilation system for the tropics using a state of the science mesoscale prediction model, and tests the effect of a sparse observational network of wind and moisture in constraining the estimate of the state. A perfect model framework is used as a necessary first step to ease interpretation of results. Ensemble assimilation allows for state-dependent error covariances, foregoing prederived balances and correlations and allowing for the use of the full nonlinear model. Boundary conditions are necessary for limited-area models, and the perturbed lateral boundaries and initial conditions are taken from a global ensemble using a non-perturbed sea surface temperature analysis. In the mesoscale model, this uniform surface had a profound effect on moisture levels in the lower levels, rapidly bringing the spread of vapor mixing ratio to near zero. Comparing the mesoscale forecast with a downscaled global model forecast showed that the interior solution was not completely dependent on the boundary conditions. Observing system experiments that assimilated synthetic moisture and wind component observations in the boundary layer and in the free atmosphere had a small effect on the state estimate when compared with an unconstrained control case. The largest improvement was in the upper troposphere obtained by observing upper-level moisture, but several analyses were degraded by the data, due in part to the sparse network and small localization radius. / by Timothy Robert Whitcomb. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1996. / Includes bibliographical references (p. 141-152). / by Chris Eliot Forest. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1991. / Vita. / Includes bibliographical references. / by Joanne Theresa Fredrich. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2004. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 37-38). / Observations of retreating subduction systems in the Mediterranean region suggest the density of subducting lithosphere is dynamically related to trench retreat rate and upper-plate deformation. Most numerical and analog studies of retreating subduction systems have not explored the effects of lithospheric density variations on subduction processes. This study is a preliminary effort to construct a two-dimensional, viscous flow model of "roll-back" subduction to explicitly examine how slab density influences retreat rate, mantle flow, and slab geometry. For a given lithosphere-mantle density contrast, the model computes the evolution of a viscous, thermal slab using a finite element code for incompressible convection (ConMan). Imposed velocity boundary conditions guide lithospheric material into a uniformly weak "subduction zone" and out into the mantle below, generating stable, asymmetric subduction. Slabs driven faster than the "intrinsic" (dynamically consistent), steady-state retreat rate of the system (vr) are characteristically arcuate, pushed upward from the base of the mantle layer by strong horizontal "return flow" beneath the descending lithosphere. Slabs driven slower than vr are sigmoidal: the slabs steepen at depth, where vertical buoyancy forces overcome lateral viscous forces set up by weak surface velocities. The diagnostic behaviors of slabs driven faster and slower than vr define a set of qualitative criteria (slab geometry, mantle flow patterns) for converging on the consistent, steady-state retreat rate of the system. For slab-mantle density contrast [delta]p = 198 kg/m³ (defined as the density difference between lithosphere at surface of the system and mantle material at the base of the system), vr ~~ 16 mm/yr. The slab is roughly planar, with 500 dip. For [delta]p = 168 kg/m³, vr is slightly slower (14 mm/yr), and steady-state slab geometry is nearly identical (moderately-dipping planar surface). It is found that the angle at which lithospheric material is forced into the mantle does not significantly affect either steady-state retreat rate or slab geometry. / by Jessica L. Haurin. / S.B.