Geological Investigation of the Mono Basing using ArcGIS

Geological Investigation of the Mono Basin using ArcGIS

Written By: Sachin Mehta

University of Nevada, Reno

Abstract

This paper entails the examination of the geological activity of the Mono Basin (Fig. 1) and the

surrounding areas of the region. Investigations performed for this research paper incorporated

the advanced spatial and map analysis software ArcGIS and its many toolsets. Three main

objectives of the research included determining patterns among fault lines and springs, charting

shorelines through time, as well as hyper spectral remote sensing of the craters in the Mono

Basin. Implementing tools provided in ArcGIS allowed us to find that no meaningful

relationship existed between the fault lines of the Mono Basin and the thermal springs located

there. Regarding other matters we focused on, it was discovered that there was a sharp decline

in water level of the Basin from 1940 to 1983 and that the water level currently resides at

1944.4 m (meters). It was important to note down these analyses because then by adding

hyperspectral imaging to the interpretation we were able to gain a better understanding of the

Mono Basin territory throughout time when creating our geodatabase.




Fig. 1: Mono Basin Region shown with surrounding landmarks

Introduction/Methodology

Examining the features of certain areas of interest can be accomplished in many ways and can

be done for many reasons. The reasons vary greatly; whether you are looking for the best

route to take to get to the gym across town, or trying to determine where would be the most

ideal location to start construction of your new home. One such medium which exists is the

geographic information system (or GIS). With it not just being a “map-maker,” this software

provides the user with a nearly unlimited amount of resources, variables, and settings to

consider. Every field of study can implement the software known as ArcGIS into their research

and/or day-to-day activities to discover relationships and spatial patterns that permeate the

geographic data that is inputted to the program.

This paper delves into the world of geology and variables’ relationships with one another;

specifically in the Mono Basin. Located near Mammoth Lakes in the Sierras, the Mono Basin




holds the oldest lake in North America—that was a product of the tectonic settings of the

region. In order to preserve the integrity of our research, different team members focused on

various portion of our research—giving us more focus on specificity.

Our main focus in developing the wide geodatabase for the Mono Basin and its surrounding

area was to answer the questions of spatial correlations between fault lines and geothermal

activity. A visual representation of this phenomenon is depicted in Fig. 2 below. This meant we

wanted to determine if thermal springs were always, for the most part, generated near the

faults and craters in the Mono Basin. With the wide array of mitigating factors, it was difficult

to analyze specifically if there was a spatial correlation between such things. Faults are the

major controlling feature to fluid flow within a geothermal region, so therefore there should be

hydrothermal regions near and around the vicinity of the fault lines in the region.




Fig. 2: Geothermal Activity and Fault Line Relationships

Another portion of the geodatabase that we wanted to develop with ArcGIS was the simple

analysis of shoreline mapping of the Mono region. Since it’s highest at about 12,000 years ago

—the reduction of the Mono Lake has been drastic. Mineralogical differences were analyzed

with the assistance of AVIRIS, which is an airborne infrared imaging spectroscopy. This data

was taken from the USGS and analyzed with ArcGIS to from the geodatabase layers for the final




output result.

The last portion of the geodatabase that we wanted to implement was the Bedrock Mapping of

the Mono-Inyo Craters. The Mono-Inyo Craters are unique in that they are an extremely young

volcanic system with eruptions occurring from approximately 40,000 years ago, to the most

recent 300 years ago. Previous work shows that the craters show a general weathering trend

apparent in AVIRIS data. To take this to the next step in investigating this trend, masks will be

created of each of the craters using high resolution aerial photography. These masks will

outline areas of bedrock, tephra, vegetation, and pumice mines that are active on several of the

craters. These masks can then be used to extract spectra from the AVIRIS imagery and show

spectral variation based on these textural and compositional differences to determine what is

type of rocks are causing the weathering trend.

Results

Spatial patterns of the Mono Basin and its surrounding regions have been identified using

ArcGIS software. The geological features of the area include a vast array of geothermal

elements including fumaroles, thermal springs, faults, and even craters. Analyses to determine

the locations of fault lines—both hidden and inferred—was performed with ArcGIS. The map

output in Fig. 3 depicts the region known as the Mono Lake with concealed faults (represented

by dash lines) and normal fault lines (represented with solid lines).




Fig 3: Concealed faults (dashed) & normal faults (solid) in the Mono Basin Region

Geothermal activity in the region was addressed using the present topography and data that

we had access to. With such information, we found that the thermal springs in and around the

Basin are controlled by the fractures (faults) and tufa ridges of the area. In addition, the

volcanic vents of the region were identified to be located at an average of 10 km from any

thermal spring. This was done by performing a Generate Near Table Analysis with the ArcMap

software.

Fig. 4: Histogram of number of thermal springs near faults around Mono Basin region




In addition, it was important to analyze areas of interest where geothermal activity could be

high and drilling could take place. Determining any correlation among the features of fault lines

and springs—and if there is any spatial pattern between them could assist in exploration studies

and reduce time & effort in answering the question of “Where should we drill?”

Performing our own investigation we attempted to uncover any relationship between the

end/start points of the many normal faults in the region and distance to a thermal spring from

those respective point locations. We developed an analysis identifying that the most amount of

thermal springs in the Mono region (~ 950) lay at a harrowing 11 km from the beginning or end

of any fault line. This insinuated that drilling near the start or end of a fault line in the Mono

Basin region would not guarantee fruitful results of hydrothermal regions.

Fig. 5: Number of thermal springs vs. distance to start/end fault line




Discussion

The various geological activity taking place around the Mono Basin Region is extraordinary—

and it being the oldest lake in North America, our analysis in this paper makes it even more

astounding. Determining the relationships among the geologic points in the region and

whether they had effects on one another answered a major question that could help in later

studies, research, and work in the area. The particular toolsets used from ArcGIS, such as the

‘Generate Near Table’ analysis was just one of the many incredible and useful ways to gather

such important data. Finding that the lake levels of Mono Lake fluctuate a great deal was

another important output that occurred from our analyses with ArcGIS. With the Mono-Inyo

and volcanic craters occurring in and around the region, our analysis on these particular

geological features could possibly help future studies take place.

The wide array of possibilities with using ArcGIS in forming our analyses was never ending. It is

not quite possible to really know whether or not the analysis performed and statistics obtained

was truly meaningful because there are other factors that are not accounted for. For example,

if the data from the USGS that we used was accurate and their locations in the correct UTM

zones were precise could have had a major effect on meaningful results for our geodatabase.

In addition, knowing additional data features—such as depths of the faults in the region, with

specific accounted numerical distances could have been applied to obtain a better analysis.

Temperature of the Mono-Inyo craters, and of the Mono Lake water itself would have been




variables that could have been applied to better our results also. There exists a wide amount of

additions we could have applied in our ArcGIS analysis to make our geodatabase even more

suitable as an end-result but in the time allotted, this Geological Investigation of the Mono

Basin & Resulting Analysis was performed with great success.

Data & Analytics

Geological Investigation of the Mono Basing using ArcGIS