Western Nevada Field Studies - November 2-3, 1998

Table of Contents:                            

Stop 1: Carson Hill Trench Paleoseismology
Stop 2:
Kyle House
Buckbrush Alluvial Fan
Ground Penetrating Radar
Global Positioning System
Plant Community  
Stop 3: Buckbrush Alluvial Fan
Stop 4: Johnson Lane Wash

alluvial fan.jpg (176636 bytes)

Stop 1 - November 2, 1998

Location:  Carson Hill Trench, Carson City, Nevada

Speaker:  Allen Ramelli, Paleoseismologist

A paleoseismologist studies past earthquakes to predict future displacement.  Aerial photographs were used to identify the fault scarps and to decide where to dig a trench.  Aerial photographs taken in the morning or at night cast shadows along the fault scarps making them easier to locate.  This fault is a branch of the larger and more active Genoa Fault.  A trench is useful for locating the fault and displacement caused by the earthquake.  Displacement is measured by correlating similar layers in the stratigraphy.  The trench is approximately 50 feet long with a maximum depth of 15 feet.  Flags were used to mark the boundaries of the soil layers. 

 

 

trench.jpg (183676 bytes)
Carson Trench sketch.jpg (126431 bytes) After the layers were identified and correlated, a cross-section was sketched.  The fault line is evident in the cross-section except in the upper layers where colluvial and alluvial deposits exist.  Colluvial deposits occur when the displacement occurs through non-water related transport.  The alluvial deposition occurs as eroded sediment is transported and deposited by water.  The presence of both types of deposition distort the stratigraphy of the cross-section. 
Stop 2 - November 2, 1998

Location:  South of Carson City on US Hwy 385, left on Stephanie Way to Johnson Lane Park. 

 

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Speaker:  Kyle House, University of Nevada, Department of Mines and Geology

The community and local government are looking to clarify the risk associated with the alluvial fan area to help developers and home owners make decisions for residential development.  The alluvial fan flood hazards pose a serious threat to the community.  A flood would bring large quantities of sediment into the resisdential area causing a large amount of damage.  Ground Penetrating Radar (GPR) will be used to identify paleochannels within the alluvial fan system instead of digging trenches which are expensive and time consuming.  Identifying paleochannels would help prove the fans are unstable and still developing.  Global Positioning System (GPS) was used to map out the locations of the GPR lines. 

Speaker:  Steve Lewis, University of Nevada, Department of Commission

The results of the GPR study will aid in clarifying the flood risk so they can make decisions on which alternative solution to use.  A moderate to severe risk would necessitate a channel diversion further upstream, which would be a costly endeavor.   Concrete ditches for channelizing the flow would minimize channel incision and erosion.  They also plan to implement the "Cows in the Pinenuts" Project.   This project calls for a transition from brush to grass on the alluvial fan.   Cattle grazing would be used to reduce the shrub population while also trampling grass seed into the ground promoting grass growth.  Grasses have a more extensive root system which reduces runoff aiding in the fan stability.   

Stop 3 - November 3, 1998

Location:   Buckbrush Alluvial Fan, Stephanie Way

On November 3rd the first GPR transect (Buckbrush) was completed. Then two other transects were done to the east on Fuller Road and Wade Street.   Laser leveling, as seen to the right,  was done along all three of these transects in order to compensate for changes in the topography. The profile that ran along Wade Street had two attenuations(distortions in the signal) that were caused by a powerlines that passed overhead and at the very end of the profile a near a wire fence.

Stop 4 - November 3, 1998

Location:  Johnson Lane Wash, south of Johnson Lane Park

GPR work was also completed at the Johnson Lane Wash, a channel that was cut by flood waters in the early 1990's.  The flow of this channel has been altered by humans in an attempt to divert flood waters away from development.  The GPR transect ran alongside the incised channel to locate older distributary channels.  

J.L. Wash- laser setup.jpg (70922 bytes)

 

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