Virginia geology

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.

 

All Maps are Not Created Equal: Blogging About Maps

~ slubkin ~ Leave a comment

The assignment is to identify two web maps and two static maps and determine the appropriateness of the medium for internet use.

Geological maps often start as topographic maps.  Topographic maps are available for download from the USGS. There is a fee for most of the maps.

My Geology 111 students use the Fredericksburg quadrangle to practice their map skills. That map can be viewed here. You can see in the image below, that this is not an ideal map for the web.

There is a lot of detail on this map, but I can’t see that detail on my monitor. The contours are barely visible. I ask my students to count contours to estimate change in elevation. This would be impossible if they had to do it on a laptop screen.

fredericksburgquad

When I was a student, I used topographic maps to make geologic maps – maps that show rock units. This is an image of a paper geologic map of Virginia stolen from VirginiaPlaces.org.

geologyva

I can see the entire map on my laptop screen. I can interpret and understand the information. But, it could be much, much better.

The USGS has created an interactive geological map of the U.S. With this map, it is possible to zoom in to a state or county and see the geology of an area in increasing detail. This is the Fredericksburg area. I was able to add County names and information from Google Earth, so I could determine where the rocks are located. fburggeo

This is great and very easy to use, but it only shows one type of information. What if I want to know about rocks and climate? One of the benefits of using a computer to view maps is that multiple types of information can be stored and viewed on one map.

The USGS and esri worked together to create the “Ecological Tapestry of the World“. This interactive map shows rock type, but it also shows bioclimates, landforms,and land cover – all at a 250 meter resolution.

Here’s Fredericksburg.ecomap

The information is also available as a layer in ArcGIS online.

On Shaky Ground Part 1: Earthquakes in Virginia

~ slubkin ~ 2 Comments

It’s been just over four years since a 5.8 magnitude earthquake in the Central Virginia Seismic Zone damaged the Washington Monument. That was a significant earthquake for our area.

Last Sunday (9/27/15) the Central Virginia Seismic Zone experienced another earthquake.  The magnitude 2.0 quake was one of hundreds of small earthquakes that have occurred in the area over the past four years. And, InsideNova feels the need to report every single one.

So, is Virginia really a seismically active area? I placed esri’s USA Earthquake Risk map on top of a topographic base map. The map shows potential ground shaking intensity from earthquakes, an estimate of the amount of damage an earthquake is likely to cause in an area.  I set the scale so the highest risk in shown in dark red while the lowest risk appears as dark blue. I added the past week’s worth of earthquakes (from esri Disater Response) to the map. You can see the our 2.0 quake in Central Virginia.

Seismic zones

Moost of Virginia falls in the medium blue range indicating a very low risk of damage from earthquakes. Our recent earthquake is small compared to the many of the other earthquakes that occurred in the U.S. last week.

It’s not surprising that the West Coast of the United States is covered in red and orange. The California, Oregon, and Washington coasts are active margins. This means that the edge of the continent coincides with the edges of one or more tectonic plates (in this case: North American, Juan de Fuca, Pacific). Geologic activity such as earthquakes and volcanoes generally occurs at the edges of tectonic plates.

The East Coast is a passive margin. The eastern edge of the North American tectonic plate is far out in the Atlantic ocean. So, geologic activity on the East Coast and most of the U.S. is relatively rare as indicated by the blue coloring.

Behind California is an area known as the Basin Range province. This is the remnant of an ancient rift zone. In the early Miocene (about 17 ma), the North American continent began to stretch and thin. But, before the continent could rift into two tectonic plates, seismic activity stopped. This left a network of faults which still responds to the stresses from activity on the West Coast. The New Madrid fault zone which underlies Alabama, Arkansas, Illinois, Indiana, Kansas, Kentucky, Mississippi, Missouri, Oklahoma, Tennessee and Texas is another example of an ancient rift zone.

But, not all rift zones are ancient. The red area in Northern New York and New Hampshire indicates activity from the St. Lawrence rift system, an active rift zone that runs along the St. Lawrence River. Perhaps one day, North America will split and a new Canadian plate will form.

If you are looking carefully you might notice that there are medium blue areas in the middle of continents far from any plate boundaries that have recently experienced larger earthquakes. Is that rifting? Does that mean we should worry?

No, it’s not rifting, but we may have reasons to worry. The cluster of earthquakes in Oklahoma includes several with a magnitude between 2.0 and 3.0. These small earthquakes have been linked to fracking rather than seismic activity. The 3.2 earthquake near Stamford, NY may also be caused by human activity. It is likely the result of water pressure from the Gilboa Dam.

Like Oklahoma and New York, Virginia has networks of ancient faults that can be reactivated by human activity. However, seismologists believe that most of our earthquakes are simply the result of old faults moving because of sea floor spreading in the Atlantic Ocean.

You can view my map here.