Santa Cruz County

Because of the great risk that landslides pose to communities, especially in California, it is essential that more predictive maps be created to help policy makers prepare for these natural disasters. For instance, these maps might encourage infrastructure improvements that could offset the damage caused by landslides. Because Santa Cruz County had soil data readily available, this county will serve as an example for a landslide hazard assessment.

Steps:

Three DEM's of the Northern portion of Santa Cruz County (which were later merged into one raster), a soil type layer for the county, major roads within the area, and fire hazard zones for California, were acquired off of the web. The DEM was first used to create a topographical map of the area that reflects elevation and elevation contours. In order to create the second map, the soil layer was first filtered to highlight ‘soft’ rock types. The fire hazard zones were then clipped to Santa Cruz county, and similarly filtered to display only 'high' and 'very high' fire hazard zones. Using the extract by mask tool, the 'soft' soil vector layer and the 'high' and 'very high' fire hazard vector layer were clipped to the elevation raster. These characteristics were important to consider because they make areas more landslide prone. When severe wildfires damage plants and soil, there is an increase in runoff after intense rainfall or rapid snowmelt, which often triggers landslides. Most importantly though, this newly clipped elevation raster was used to create a slope layer which was then reclassified based on slope grade. 31-65% slope was considered to be a 'high' hazard area (orange color), as this is generally within the range that landslides are most likely to occur. Finally, I created a 1,000 foot buffer around major roads, and again used the extract by mask tool to highlight selected regions within the buffer as 'very high' landslide hazard areas (red color). This is because because damage to roads following landslides, can not only put a great number of people using the roads at an immediate risk, but it may also cause a great inconvenience to communities thereafter. Just last year, a landslide along Highway 1 in Big Sur, California lead to a road closure for over 6 months. With that being said, selected locations, specifically within close proximity to a major road, should be taken into consideration as soon as possible in order to properly prepare infrastructure to withstand landslides. Ultimately, it should be noted that all areas highlighted in the above map will be even more susceptible to landslides following an extremely wet season, weathering, or a great loss of vegetation through events such as wildfires.

Conclusion

From the historic map of landslide deposits, along with photos included throughout this website, it is clear that landslides can cause severe damage and should not be considered lightly. Unfortunately, to the average viewer, the landslide hazard map I produced on its own might actually undermine this reality, as it appears that a majority of Northern Santa Cruz County is in the "clear" and not as risk for landslides. However, the truth is that landslides have the capacity to cover a lot of territory (as the historic landslide deposit map proves). Thus, it is integral that policy makers investigate and understand more about the topography of these at risk areas in order to protect communities from severe destruction. For instance, it is important to remain cautious when building new homes, and prevent construction within a certain distance from cliffs.

Ultimately, in completing this project, I think the fact of the matter is that it might be difficult for the general public to realize the magnitude of landslides from solely a landslide hazard map, like what I created. This is because on paper the areas at risk appear minimal, and thus somewhat trivial. Experiencing the potential negative effects of landslides, like losing a home for instance, is much more powerful in getting communities to truly understand the severity of these natural disasters.