GIS

Mapping Rising Seas

~ slubkin ~ Leave a comment

According to U.N. Secretary-General Ban Ki-moon, climate change is “one of the most crucial problems on Earth”. That’s because climate change means more than just rising temperatures and shrinking glaciers. Climate change also means shifts in weather patterns, stronger storms, longer and more severe droughts, changes in the distribution of agricultural pests and diseases, increased wildfire risk, greater ocean acidity, and sea level rise.

For my semester project, I chose to model sea level rise at Wallops Island, Virginia. I visited Wallops Island in April as part of the STEM Takes Flight Sea Level Rise/Invasive Species Service Learning Course. I will write about that experience in another post.

Wallops Island is a barrier island off Virginia’s Eastern Shore. It is a wildlife refuge and home to NASA’s Wallops Flight Facility, which is NASA’s center for the management and implementation of suborbital research programs. Because of Wallops Island’s location, it is especially vulnerable to sea level rise.

Satellite measurements (NOAA, 2016) show that since 1992, global sea level has been rising at an average of 0.11 inches per year. However, in Virginia’s barrier islands, sea level is rising at twice that rate, an average of about 0.22 inches per year (NOAA, 2016).

When you think of a quarter inch, it really doesn’t seem like very much.Why is this a big deal?

In places like Wallops Island where elevation is close to sea level, small amounts of sea level rise can result in large losses of land. At the current rate of sea level rise, most of the island will be gone by 2040.

Here are some maps I created of land loss on Wallops Island. In this image, land is represented as black and water is represented in color.

Sea Level Rise

Sea level rise is not a new problem for Wallops Island. Land in the Chesapeake Bay area is subsiding or sinking because the Earth is still adjusting to the recession of the glaciers from the last ice age about 12,000 years ago. However, land subsidence increases the rate of relative sea-level rise, and this is why the Virginia coasts have the second highest level of sea level rise in the U.S.

Because of subsidence, the coastline of Wallops Island has moved steadily shorewards from 1851 (earliest data available) to 1962.  However, since 1962, NASA interventions, including a sea wall completed in 2012, have restored much of the shoreline. The 2014 and 2011 coastlines showed the least encroachment because of these interventions.

Even with the sea wall, constant maintenance is required to prevent the beaches from losing 10 to 22 feet of coast to erosion each year.Coastlines

As the Earth warms, rates of sea level rise will increase. It will become harder and more expensive for NASA to counteract the loss of land and protect its facilities.

For a video and more information about sea level rise, Wallops Island, and the methods used in my project,  visit my online story map.

 

Tobler, Steno and Geologic Maps

~ slubkin ~ 3 Comments

Waldo Tobler is a geographer at my alma mater, UC Santa Barbara. He is known for Tobler’s Law or the “first law of geography” which states “Everything is related to everything else, but near things are more related to each other than distant things.”

My classmate Sunil Bharuchi recently published a discussion of Tobler’s Law on his blog, GIS 295 Web GIS. He included this image, which explains spatial auto correlation.

Spatial autocorrelation measures how well a set of spatial features and their values are clustered together in space. A spatial feature is a point, line or polygon that identifies the geographic location of a real world object; this object could be a building, a forest, a rock unit or a lake.

According to Tobler’s law, spatial features will be clustered next to more similar spatial features – this is illustrated in the first image above. But, is this always true? Sunil’s post got me thinking.

Here is a geologic map of Yosemite National Park. Which of the images above does it look like?

Map of Yosemite National Park.svg
“Map of Yosemite National Park” by General_geologic_map_of_Yosemite_area.png: en:United States Geological Survey derivative work: Grandiose – This file was derived from  General geologic map of Yosemite area.png: . Licensed under CC BY-SA 3.0 via Commons.

I’ve spent years looking at geologic maps, so I told Sunil “image three looks more like geology.” But, does that mean Tobler is wrong?

Not at all.

Nicolas Steno (Niels Stensen, 1638-1686) was a Danish scientist and bishop who made important contributions to the fields of anatomy, paleontology, crystallography and geology. Steno’s principles of statigraphy explain the formation of sedimentary rock and are still used by geologists to determine the history of a rock unit. There are three principles:

  1. The Principle of Superposition: When sediments are deposited, the sediment that is deposited first is at the bottom while sediment that is deposited later is at the top. Therefore, the lower sediments are older.
  2. The Principle of Original Horizontality: Sediment is originally deposited in horizontal layers.
  3. The Principle of Original Continuity: Sediment is deposited in continuous sheets that only stop when they meet an obstacle or taper off because of distance from the source.

Doesn’t the Principle of Original Horizontality sound a lot like Tobler’s Law? Then why don’t geological maps look like the first picture on Sunil’s image?

First of all, sedimentary rock isn’t the only type of rock on Earth.Steno’s principles do not apply to igneous and metamorphic rock.

Second, the Earth is an active planet. Plate tectonics causes sedimentary layers to bend, break and even overturn. Igneous rocks intrude into existing rock from below the Earth’s surface or erupt from above. These processes mean that geologic units are often very complex and the resulting spatial patterns reflect that complexity.

Yosemite USA.JPG
“Yosemite USA” by GuyFrancis – Own work. Licensed under CC BY-SA 3.0 via Commons.

James Hutton (1726-1997) was a Scottish physician and geologist who is known as the founder of modern geology. He was the first to suggest that the Earth is continually being formed and that based on the rates of geologic processes, the Earth must be much,much older than the accepted estimate of a few thousand years. He is also known for the Law of Cross-cutting Relationships.

Law of Cross-cutting Relationships: If a fault or other body of rock cuts through another body of rock, then that intrusion must be younger in age than the rock that it cuts or displaces.

It is this Law of Cross-cutting Relationships that helps us interpret geological units and create geological maps.

Can you figure out the temporal relationships in this cross section?

geology
From Earth: Portrait of a Planet, 4th Edition (2011) by Stephen Marshak.

So, how does Tobler’s Law fit in? It depends on scale. If you are standing on an outcrop of sandstone, chances are good that the rock surrounding you will also be sandstone – especially if you are in the tectonically quieter center of a continent. But, If you are mapping Yosemite park using one kilometer pixels, you will find a lot more variation in neighboring areas.

 

Introductions

~ slubkin ~ 3 Comments

Hi, I’m Sara Lubkin. I am a GIS certificate student at Northern Virginia Community College.

I am also a geologist who studies fossil insects, paleoclimate and the current effects of climate change. I earned my PhD from Cornell University in 2008 and worked in web and social media marketing for a while.

I now teach introductory geology classes at the University of Mary Washington. When I’m not teaching or learning, I do research. I am currently collaborating with the NASA DEVELOP Program and the Virginia Institute of Marine Science on a project tracking harmful algal blooms (HAB) in the Chesapeake Bay. I am also a mom.

For me, GIS is connecting data to geography. When non-scientists ask me what GIS is, I tell them that I put information on maps so I can better analyze and interpret.  I was a scientist before I studied GIS, but GIS has allowed me to ask and answer different types of questions.

Before studying GIS, my fossil insect research focused on describing new species and determining how species were related to other species and modern species. I was getting frustrated with this work and wanted to do something more meaningful. Now, I am able to connect Pleistocene fossil insect species to specific climate zones and create maps of Pleistocene glaciation. I am hoping to use this research and my work with NASA DEVELOP to transition into the study of climate change and its effects on the Earth.