Topics to Research Using GNA

Your Task: You are to select from the list below a topic to research and present to the class. The accompanying paragraph will give you an introduction to area and its geologic significance. Use gna to make at least 5 images (maps or profiles) that effectively convey the geophysical patterns found in the area. Your set of images should include a location map that orients your audience. Remember that base maps can be made with topography as well as gravity and that a variety of profiles are possible.

Caribbean Islands vs. Cascades

The Cascade Mountains and the Caribbean islands are similar in that the are both large mountain ranges. If you consider their height from the ocean floor, the Caribbean Islands are huge. The origin and internal structure of the two ranges are quite different, however. The Caribbean Islands are created when the North American ocean plate is pushed under Caribbean plate ocean plate. The lower plate partially melts and magma moves up to erupt as volcanoes. The volcanoes have grown large enough to be islands. The Cascade Mountains have volcanoes capping the range but most of the crust is ocean floor mixed with granite-like material, and overall, is very thick. These two ranges will have very different gravity patterns.

Make some gravity maps and profiles that effectively reveal the patterns of gravity. Look for an explanation for the differences that can be observed.

Aleutian Trench/Subduction Zone

This region is a major boundary between two plates. The Pacific Plate is moving to the north and has been driven under the Alaska and the Bearing Sea. The Pacific Plate partially melts at great depths and magma moves up to the surface to form volcanoes. The volcanoes that are large enough to breach the surface and form the Aleutian Islands. This type of plate boundary has a distinct gravity pattern. It also has a distinct earthquake pattern.

Create some gravity and earthquake maps that best reveal these patterns. Also create some profiles that compare bathymetry to gravity.

Juan de Fuca Plate Boundaries

The Juan de Fuca Plate is one of the worlds smallest plates. It is located offshore of Washington, Oregon, Northern California, and southern British Columbia. Like any plate, the edges of the Juan de Fuca plate experience slow but constant motion. Most earthquakes of the Pacific northwest outline the plate. Gravity anomalies outline the edges of the plate.

Plate boundaries, in general, are categorized into 3 types. The categories are based on the relative motion of the 2 plates that are juxtaposed. The Juan de Fuca plate has all three types of plate boundaries.

Explore the earthquake and gravitational patterns that define the plate boundaries. Create images that show how these patterns differ at the 3 types of boundaries. Create some profiles that compare topography/bathymetry to gravity.

Washington Physiography and Geophysics

The state of Washington can be divided into several different physiographic regions. Each region has a distinct texture, history and geophysical signature. Refer to an article that outlines the regions for you. Explore the patterns of gravity and earthquakes for the state. Focus in on the boundaries between the regions. Make some maps and profiles that best illustrate these patterns.

Passive vs. Active Continental Margins

The edge of the continent is referred to as the continental margin. If a margin is coincident with a plate boundary there are earthquakes and possibly volcanoes. This is an active continental margin. If the margin is not a plate boundary then it is usually more peaceful. A great place to contrast these two types of margins is in Central America, in the area of Nicaragua. The west margin is where the Cocos plate is subducting under the continent. This margin has active volcanoes and earthquakes. The eastern margin is passive. Make some maps and profiles that reveal these differences.

Earthquake History of Washington

Is Washington earthquake country? A lot of attention and preparation is being given to the possibility that Washington could experience a strong earthquake. Many people have lived in Washington for years and claim to have never experienced one. Use GNA to explore this question. With the flexibility of the program you can find out when and where earthquakes have occurred. You can select for time and magnitude in order to make generalizations about what kinds of events are most common and most infrequent.

Snake River Plain and Yellowstone

One of the most important pieces of evidence supporting plate tectonics is the hot spot track. A hot spot is a location where hot sub-crustal magma continually ascends toward the surface. The hot spots appear to be fixed in their location while the over riding plate moves along over it. Yellowstone is a hot spot that exists today under northwest Wyoming. The Snake river plain of southern Idaho is a broad low elevation valley that is floored by basalt. The age of the basalt trends from 1 million years on the east to 6 million years in the west. In other words the basalt of the snake river plain are the remnants of the Yellowstone hot spot produced as North America traveled to the west. Some researchers think the basalt of eastern Washington are also products of the hot spot.

The dense basalt leave a high gravity anomaly especially when compared to the granite of central Idaho. Make some revealing maps and profiles that show the location of this hypothetical hot spot track using gravity maps, contours and profiles.

Oregon-Washington Coast Ranges

The Oregon-Washington Coast Ranges where named for their geographic location, near the coast of the named states. Geologically they are internally consistent from just north of the Oregon Border to the southern tip of Vancouver Island. This shows up well on a gravity map. The origin of the rocks is that of an ocean island. The Mountains where once an ocean island chain much like Hawaii. As the ocean plate converged with North America, eventually the islands collided and became stuck onto the continent. They where too large to become subducted. As the islands came close to the continent, sediments from continental rivers where deposited onto the volcanic rocks. The volcanoes remained active so the sandstones are seen inter-layered with basalt. Gravitational highs show the location of the basalt, which in some areas are as much as 20, 000 feet thick.

San Andreas Fault

The San Andreas Fault is famous due to it's frequent earthquake history. What many people don't realize is that it is also a major plate boundary. The Pacific plate slides northwestward along the North American plate. The fault itself is more that just one crack. It is more accurately thought of as a fault zone. There are many sub-parallel faults near the San Andreas. Use gna to find out when, where and how large earthquakes are on the San Andreas. Look for gravitational patters as well. Because faults are weak zones or fractures in the earth's crust, weathering processes have caused valleys to develop along them. Your images should zoom way in on a section of the fault so that a profile can be drawn that shows the valleys.

Mid-Continental High and Nearby Low

The ancient core of the continent is buried by up to kilometers of younger rock layers. Geophysical studies of the mid west reveal gravity anomalies that allow to infer about what the ancient crust may be like. The mid-continental gravity high may be an ancient continental rift that did not develop into an ocean. The rocks are probably high density basalt. Nearby is a granitic body that creates a gravity low. With gna you can create maps and profiles that show us the gravity of the ancient continent.

Rocky Mountains vs. Appalachians

The Rocky Mountains tower above all others of the lower 48 states. The Appalachians, however, used to be much larger. They were formed 3-400 million years before the Rocky's and were the result of a collision between Africa, North America and Europe. In the immense gulf of time, erosive processes have diminished the Appalachians to rolling hills. As the upper regions of the mountain range is removed the roots of the mountains are exposed. Because the continents tend to be buoyed by the mantle, lightening a mountain range will cause it to move upward. This is called isostatic compensation. The gravity over Appalachians is low due to the existence of its root, but its root is shallow due to isostatic compensation.