Miriam Nnadili

December, 2010

GEO 326G/387G

GIS Final Project: Delineation of landslide-prone areas on basis of slope,

soil and/or geology grids in Yosemite National Park, California

Introduction

Problem Overview

For this project, I have will be delineating the landslide-prone areas at the Yosemite

National Park, California. I also formulated a method to determine this land slide prone

areas in the park by ranking certain features such as the elevation which was used to

calculate the slope, permeable rocks and vegetation within the park. The landslide prone

areas were then determined using the Spatial Analyst Tool within ArcGIS. This study

shows that permeable rocks and vegetation has an effect on landslide most especially in

areas where the elevation is slow. Furthermore, since Yosemite National is well known for

the high amount a snowmelt (waterfall) within a short period and the large human

activities in this area the water flow line will also be used to delineate the areas that are

will be prone to landslide.

Background

Yosemite National Park is located in the central Sierra Nevada of California and it is one

of the first wilderness parks in the United States, is best known for its water falls, but

within its nearly 1,200 square miles, you can find deep valleys, grand meadows, ancient

giant sequoias, a vast wilderness area, thousands of lakes and ponds and much more. The

park has an elevation range from 2,127 to 13,114 feet (648 to 3,997 m) and contains five

major vegetation zones: chaparral/oak woodland, lower montane, upper montane,

subalpine, and alpine. The geology of the Yosemite area is characterized by granitic rocks

and remnants of older rock. The geologic story of Yosemite National Park can be

considered in two parts: (1) deposition and deformation of the metamorphic rocks and

emplacement of the granitic rocks during the Paleozoic and Mesozoic; and (2) later uplift,

erosion, and glaciation of the rocks during the Cenozoic to form today’s landscape

Yosemite is famous for its high concentration of waterfalls in a small area. Numerous

sheer drops, glacial steps and hanging valleys in the park provide many places for

waterfalls to exist, especially during April, May, and June (the snowmelt season). Located

in Yosemite Valley, the Yosemite Falls is the highest in North America at 2,425-foot (739

m). Also in Yosemite Valley is the much lower volume Ribbon Falls, which has the

highest single vertical drop, 1,612 feet (491 m). Yosemite's hydrologic resources are

fascinating to examine because the park lies at the heart of one of the most extreme

Mediterranean climates on earth. Such climates are characterized by cool, wet winters and

long, dry summers. In the case of Yosemite, most precipitation falls in the form of snow

that accumulates above 6,000 feet (1,830 meters) during the winter, making a natural

water tower that slowly releases melt-water through the spring and early summer. This

slow release of water nourishes lower regions well into the hot dry season.

Objective

The objective of this study is to determine the areas that are prone to landslide on the basis

of slope, soil and/or geology grid and water flow area/line. For this analysis, the ArcGIS

software will be used.

Data

Data required

1) Elevation (DEM)

2) Geologic Map

3) Hydrographic data

4) Boundaries, land use and land cover

Data acquisition

In other to delineate landslide prone areas, the Digital Elevation Model (DEM) was

downloaded from the USGS seamless server which is available to the public

(http://seamless.usgs.gov/website/seamless/viewer.htm), and in other to download this file

from the server, I highlighted the region to be downloaded. Other additional features

(boundaries, land use, land cover, roads, and streams) were also downloaded from this site

by selecting the areas of interest from the drop down menu in the download button and

display button and then highlighting the area within the Yosemite National Park which is

my area of interest (Figure 1) a new window appears with an option to download all the

files selected.

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GIS data

portion of

water flow

Based on the analysis performed during this research, it is evident that the potential for

landslide in this area is not high although various factors was ignored during this analysis,

such as morphological factors (slope angle, vegetation change, erosion, uplift, rebound),

physical factors (rainfall, snow melt, earthquake, ground water changes, surface runoff,

seismic activity) and some geologic factors, this was due to the time limitation and

challenges faced in trying to get some of the data for this analysis.

Finally, it can be concluded from the Figure 16 that areas in brown are most likely to be

brown to landslide, this result was drawn as a result of the low vegetation and soft rocks

present in this area. Also the presence of multiple water flow line in this area can result to

landslide and Yosemite is known for its high amount of snowmelt (waterfall).