By Richard Pratt, Denver Museum of Nature and Science

Glacial Lake Riverton formed in the central Wind River Basin during the Bull Lake (Illinoian) glaciation around 140,000 years ago. At its maximum extent, the lake stretched 95 miles east-west, 57 miles north-south, and could have been 700 feet deep. The lake overflowed through Arminto Gap into the Powder River drainage. This eastern overflow stabilized the lake level at about 6,100 feet elevation; however, the absence of a pronounced valley or canyon indicates that the flow was never large. The west end of the lake was dominated by the Bull Lake glacier spewing icebergs directly into the lake. Erratic material in the form of large, angular, exotic drop-stones and partially sorted shoreline gravel is distributed around the lakeshore; it is particularly concentrated in the far northeast where icebergs were blown by dominant westerly winds. A fine-grained rose-pink granite and a quartz-rich spotted gneiss along with the general suite of light metamorphic rock types can be traced directly to the Bull Lake moraines that define the extent of the lake. Shoreline physiographic features are mostly obliterated by subsequent pedimentation and stream erosion except near Arminto Gap where a well-preserved beach ridge was found.

Glacial Lake Riverton drained by stream capture and diversion through Wind River Canyon. The diversion probably occurred when a southward-heading stream from the Big Horn Basin tapped through the Paleozoic karstic limestones (Madison Limestone or Bighorn Dolomite) to initiate the drainage flow. The Bull Lake (Illinoian) timing of this event has broad implications for the erosion history for both the Wind River Basin and the Big Horn Basin.

By Matt Sares, Colorado Geological Survey

As of 2005, renewable energy sources supplied almost 9 percent of the electrical power supply in the U.S. Of the total renewable energy sources, conventional hydroelectric energy supplied 80.8 %, biomass 9.2 %, wind 5.4 %, geothermal 4.4 % and solar 0.2 %. Most of the U.S.’s geothermal activity takes place in California and Nevada, but Alaska, Hawaii, and Utah also have some generation. New Mexico, Idaho, and Oregon have new projects underway in various stages of development.

Currently, geothermal resources in Colorado are used directly for recreation (pools/spas), greenhouse agriculture, aquaculture, space heating, and district-wide heating – but not for electrical power. Several lines of evidence indicate that the geothermal potential for Colorado may be underestimated in regard to electrical generation:

1. High heat flow – Colorado has the second largest heat flow anomaly in the U.S.
2. Quaternary volcanism (occurring within the last two million years) – Colorado has five such volcanoes
3. Quaternary faulting (younger faults have more potential) – Colorado has over 90 such faults
4. Rift zone tectonics in the San Luis Valley and upper Arkansas River basin.
5. A low-velocity seismic P-wave anomaly in central Colorado, The Aspen Anomaly, indicates a significant area of less dense, warmer upper mantle. This could contribute to higher geothermal gradients in the area.

Two sedimentary basins in Colorado indicate potential for geothermal resources at depths in the range of existing oil and gas wells. Oil and gas fields in the Denver Basin have recorded bottom-hole temperatures that range between 200-250°F at roughly 10,000-11,000 feet. Similarly, bottom-hole temperatures in the San Juan Basin south of Durango have recorded temperatures ranging from 150 – 250°F at depths of between 6,500 – 9,000 feet. Twenty of these wells have temperatures of 250°F or more

The Colorado Geological Survey, using data from thermal springs and wells, mineral exploration holes, and geothermal test holes, has constructed statewide maps of geothermal heat flow and geothermal gradient to identify the most prospective areas for geothermal resource development. These maps can be used to assist in identifying locations for conventional shallow hydrothermal systems as well as areas where enhanced geothermal system technology can be applied to tap deeper geothermal resources, 10,000 to 30,000 feet deep in the earth’s crust.

The pool at Ouray

By Matt Morgan

We had an outstanding turnout for the February program at the American Mountaineering Center. Over 55 members and non-members saw the lecture by Dr. Peter Molnar who presented "The Gradual Closing of the Indonesian Seaway and the Onset of Northern Hemisphere Ice Ages", a topic which is both quite relevant to the "Global Warming" debate and scientifically controversial. What made the night very special was the after the lecture, a large majority of the attendees stayed around to mingle and chat. In my view, this was due to 1) the lecture topic, which brought out the great numbers and, 2) the smaller and more "friendly" room that made it easy to network. We were unable to hold our meeting in the large auditorium due to a scheduling conflict. In the future, we may hold the regular meetings in this smaller room, which by no means will diminish the prestige of the CSS. In fact, it may gain us a new foothold!

Having relevant and newsworthy topics brought out several non-members that came to me afterward and said they would like to join. They stressed the importance of having timely scientific presentations, which will be a focus for 2008. However, we will mix in some not-so-scientific presentations to keep things fun.

Also, the next few months will be a busy time for the CSS. We will have Family Day in April and field trips in May and June. Stay tuned for more details!

When: Saturday, May 17

Departure Site: Cold Springs Park-N-Ride, Lakewood @ 7:30 am

We will begin this field trip by traversing the southern Front Range, following Highway 285 to our first stop at Kenosha Pass. Here, we will observe probable Quaternary normal faulting and structural relationships involving tensional faulting overprinting pre-existing Laramide structures. Continuing to the southwest, we will proceed to look at the Elkhorn thrust, high frequency footwall folding, and syn-tectonic conglomerates. We will also look at new geophysical and hydrological data that constrain the configuration and the extent of the fault zone, and briefly discuss its implications for fluid flow in the South Park basin.

In the afternoon we will examine late Eocene to Miocene volcanic and sedimentary rocks in southwestern South Park and discuss the structural deformation that affects them. Evidence of regional and local evaporite dissolution and collapse, including salt springs, sinkholes, large topographic depressions, and synclines will also be viewed. One field trip stop will briefly describe new information on Late Paleozoic stratigraphy and how that data has led to the discovery of major east-west-trending, Laramide-age faults. If time permits, our last stop will be in a Pleistocene paleovalley that was abandoned at the end of the Pleistocene or early during the Holocene.

Sack lunches and transportation will be provided.

Check the next issue for costs and registration

John Lufkin is hosting a hiking retreat in northern Costa Rica, March 17-25. The cost is $2050, including airfare, 7 nights’ lodging in a cabin in Finca La Anita, all meals, a 4-wheel drive vehicle, hiking trips and boat rides. Geology will not be the focus of the trip. Trip is limited to 20 participants. Contact John Lufkin, 303-284-2646, lufk3@comcast.net. Website: www.laanitarainforest.com.

Earth Science Meetings and Talks

Newsletter items must be received by the 25th of each month.

Items may include special events, open houses, etc...thanks!

27th Avenue, Lakewood. Social hour 6:00-7:00 p.m. Technical presentation at 7:00 p.m. Meetings are normally scheduled

for the first Monday of each month. Mar 10, Willy Lynch, ESRI, "How to use GIS with mine and geology data". For information contact Jim Piper, (303) 932-0137, or the website http://www.dregs.org.

technical talk at the Wynkoop Brewery begins at 11:30 a.m., 18th and Wynkoop Sts. in Denver. Subject matter usually deals

with the application of well logs to oil and gas exploration. Call Eleice Wickham at 303-573-2781 for reservations. Web page: http://dwls.spwla.org.