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In recent years, an international consortium of research organizations conducted investigations at the Chicxulub Crater in Yucatan, Mexico, to better understand the crater’s formation mechanisms and the effects produced by the impact of the asteroid that is hypothesized to have caused one of the major life extinctions on Earth. This study aims to reproduce the asteroid’s impact mechanics by matching computer simulations obtained with the use of the distinct element method (DEM) against the latest topographic data observed across the crater footprint. A 2D model was formulated using ITASCA’s PFC2D software to reproduce the asteroid’s impact on Earth. The model ground conditions prior to impact were replicated based on available geological and geophysical field information. Also, the proposed DEM model configuration was designed to reproduce a far-field effect to ascertain the energy dissipation of the asteroid’s impact at the model’s boundaries. Impact conditions of the asteroid were defined based on previous asteroid impact investigations. A parametric analysis including the asteroid’s impact angle and the asteroid’s impact velocity was conducted to assess their influence on the crater formation process. Results of the simulations included the final crater topography and stratigraphy, stress profiles, contact force chains, and velocity fields. Numerical simulations showed that both the asteroid velocity and impact inclination play a major role in the crater formation process, and that the use of DEM provides interesting insights into impact crater formation.

Models based on generalized plant physiological theory represent a promising approach for describing vegetation responses to environmental drivers on large scales but must be tested for their ability to reproduce features of real vegetation. We tested the capability of a generalized vegetation model (LPJ-GUESS) to simulate vegetation structural and compositional dynamics under various disturbance regimes at the transition between prairie, northern hardwoods, and boreal forest in the Great Lakes region of the United States. LPJ-GUESS combines detailed representations of population dynamics as commonly used in forest gap models with the same mechanistic representations of plant physiological processes as adopted by a dynamic global vegetation model (the Lund-Potsdam-Jena [LPJ] model), which has been validated from the stand to the global scale. The model does not require site-specific calibration. The required input data are information on climate, atmospheric CO2concentration, and soil texture class, as well as information on generally recognized species traits (broad-leaved vs. needle-leaved, general climatic range, two fireresistance classes, shade-tolerance class, and maximum longevity). Model predictions correspond closely to observed patterns of vegetation dynamics and standing biomass at an old-growth eastern hemlock (Tsuga canadensis)/hardwood forest (Sylvania Wilderness, Michigan), an old-growth forest remnant from the \"Great Lakes Pines Forest\" (Itasca State Park, Minnesota), and a presettlement savanna (Cedar Creek Natural History Area, Minnesota). At all three sites, disturbance (wind or fire) strongly controls species composition and stand biomass. The model could be used to simulate vegetation dynamics on a regional basis or under past or future climates and atmospheric CO2levels, without a need for reparameterization.

We studied the life history and feeding habits of two coexisting and closely related sister species of Sialis (Sialis itasca Ross and Sialis velata Ross) from a reservoir and river in central Texas. Measurement of larval head capsules and emergence showed the two species to have 10 larval instars, and the seasonal distribution of immature and adult life stages showed synchronous, seasonal, univoltine life histories with a single cohort. Life history dynamics were somewhat faster in the river, probably due to higher temperatures during the larval growth periods. Larvae exhibited a more rapid larval development rate and earlier prepupal and adult emergence patterns relative to those reported from more northern latitudes. However, a univoltine life cycle appears to represent the norm for Sialis in geographic locations where water temperatures are not limiting to growth and suggests that evolutionary/genetic constraints play a greater role in regulating life history in these insects than environmental factors. Analysis of larval diets showed prey consumed by members of both populations consisted of ostracods, oligochaetes and chironomids.

This study of the scientific production of nature at the Mississippi headwaters at Lake Itasca, Minnesota shows how national imaginings of geography were territorialized in the landscape and made available to an imagined national community. The exploration of the Mississippi, the establishment of its source, and the creation and maintenance of the headwaters landscape are all part of the geographic project of making the territory of the nation appear as a collection of timeless natural objects, a cultural process that accompanied the violent appropriation of indigenous land through which national territory was acquired. Because of the symbolic importance of the Mississippi River, its social construction as a \"natural\" object played a key role in constituting national territory, an imperialist project that simultaneously depended on and helped erase indigenous conceptions of and claims on the land. The landscape at Itasca State Park sustains this process and keeps it alive today.

Charcoal stratigraphic analysis and fire scars on red pine (Pinus resinosa) trees were used to determine spatial and temporal occurrence of fire in 1 km^2 of old-growth mixed conifer/hardwood forests in northwestern Minnesota. Charcoal was analyzed year by year on petrographic thin sections from annually laminated sediments of three small (@<5 ha) lakes having adjacent catchments. Dated fire scars (n = 150) from recent treefalls provided an independent record of the spatial patterns of past burns. Sedimentology of the varved sediments, water-balance models that use 150 yr of instrumental temperature and precipitation data, and published data were used to identify climate changes in separate studies, and they were used in this study to examine the possible connection between changing fire regimes and climate change. Fire-history data were used to show the changing probability of fire with time since the last fire and the effects of spatial variance (slope and aspect) on the distribution of fires through time. Over the last 750 yr, fire was most frequent (8.6 @+ 2.9-yr intervals) during the warm/dry 15th and 16th centuries. Intervals were longer (13.2 @+ 8.0 yr) during cooler/moister times from AD 1240 to 1440 and since 1600 (the Little Ice Age). The fire regime during the Little Ice Age consisted of periods during the mid-18th and mid-19th centuries characterized by longer fire intervals of 24.5 @+ 10.4 and 43.6 @+ 15.9 yr, respectively, and short-term warm/dry periods from 1770 to 1820 and 1870 to 1920 when intervals were 17.9 @+ 10.6 and 12.7 @+ 10.1, respectively. The probability of fire increased through time, probably in step with fuel accumulation. South- and west-facing slopes burned more frequently than did north and east aspects. Fire suppression began in 1910. During warm periods, probability of fire was sufficiently high that a continuous litter layer was all that was necessary for fire to spread and scar trees. During cool and moist times fire was most likely to occur in years with higher moisture deficits. The combined methods for fire-history analysis provided a more detailed spatial and temporal documentation of fire regimes than has previously been possible from analysis of fire scars or of charcoal counts derived from fossil pollen preparations. Results support predictions of particle-motion physics that thin sections record a local fire history. Because climate varies continuously, the responsiveness of disturbance regime to short- and long-term climatic change suggests caution in the interpretation of fire frequencies that derive from space/time analogies or extrapolation from short-term data.

Rosemary E. Vecchio ITASCA - Rosemary E. Vecchio, 87, of Itasca for 9 years, formerly of Roselle for 45 years, passed away October 17th at Friendship Village in Schaumburg. Rosemary was a retired cashier for 30 years at Lake Park High School. She was the beloved wife of the late Anthony B. (1984); loving mother of Cheryl A. (Robert Jr.)

  Larry Coutre ITASCA - Larry Coutre, 68, a proud Vietnam veteran, was born Dec. 31, 1947, in Chicago, and passed away Aug. 17, 2016, at the Hines Veterans Hospital, Hines, IL.

[...] the whole park is a real jewel, but because of its location, it's overlooked. Itasca State Park also provides all kinds of interpretive offerings -- from campfire programs and nature hikes to musical performances and children's activities -- every day during the summer and fall, and weekends during spring and winter.

Anna Varacalli ITASCA - Anna Varacalli (nee Colantonio), age 78, beloved wife of Salvatore P.; devoted mother of Steve (Debra), Dave (Debbie) and Lisa (Bob) Parla; dear sister of Teresa Forte, Anthony (Pat), Ernesto (Anna) and...