seafloor science

Rita will post an activity to measure the seafloor spreading in the MAR (mid-Atlantic Ridge) and in the EPR (East Pacific Rise) here in a couple days. 1-30-2007

This exercise to determine whihc is spreading faster came to me from Andrew Goodwillie at Lamont-Doherty, where GeoMapApp was developed. Try it and then you tell me which is spreading faster by looking at the colors.

A teacher has asked if the Pacific ridge is separating
as fast as the MAR?

This can be answered very nicely in GeoMapApp. Here's how.
Open GeoMapApp. In the database tab (upper left) select the
last item - Other Data sets (Hosted). Double-click on the
Tectonics folder. Click once on Peter Bird's Plate Boundaries
and hit OK. Keep hitting OKs until the grey circles are
plotted on the map. In the right pane, select Colour Symbols.
In the new little window that pops up, go into the drop-down
menu and scroll down to "divergent component mm/a". Hit OK.
The circles turn largely yellow-ish, and a colour palette
window opens. In the colour palette, put the mouse on the
left grey line (located around -230) and drag the line
towards the right to zero. Most of the circles become blue.
Now use the zoom tool to zoom in on the EPR/MAR area.
In the colour palette, drag the right grey line to,
say, 150 mm/a. The EPR circles are yellow/pink/orange
whilst those on the MAR remain light blue.

Here, the colours are instantly showing us the spreading rate.
Lighter colours indicate faster spreading. You can also click
on any of the circles and this will highlight the data point
in the table below. Scroll to the right and you'll see the
divergent rate for that particular point.