Seafloor Cake

I made this seafloor cake for a Girl Scout meeting a while back. It was so much fun assembling all the components and using it as an oceanography STEM learning activity. And it's fun to eat!

The objective of the activity was to learn about the layers of oceanic crust much the same way oceanographers do - by coring. We tried a few different types of coring devices, including fat straws and biscuit cutters to investigate the composition and distribution of the layers of the seafloor cake. The cake I made was pretty flat so the layers were not as easy to identify. Perhaps next time it would be better to have more of a columnar cake.

This cake is structured based on the structure or layering of oceanic crust. These layers include (from deepest to shallowest):

1. Mantle Rock or Peridotites - mainly composed of the minerals olivine and pyroxene (green to brown in color) and is ductile

2. Gabbro - Intrusive igneous rock (crystalline magma that solidifies underground) and rich in iron (dark brown to black in color)

3. Sheeted Dikes - Intrusive igneous basaltic layer arranged as vertical columns (dark brown to black)

4. Pillow Basalt - Extrusive igneous rock (extruded magma that solidifies above ground) that is glassy (little to no crystals) because it is quenched by cold seawater (brown to black in color)

5. Sediment - Mud, or "ooze" that is deposited over time as surface-dwelling organisms, primarily phytoplankton and zooplankton, sink to the bottom of the ocean. Seafloor sediment will be thicker the older the crust is, or the further away from the spreading ridge, or if the crust is closer to land and receives lots of nutrient input and thus is highly productive.

Besides the rocky layers of the crust, there are regions of crustal spreading where magma wells up to create new solid crust as the tectonic plates are being pulled apart. This usually takes place at mid-ocean ridges, and these have fluid magma chambers dotted all along their length. There are also areas of new crust being formed over hotspots or as a result of other tectonic processes. Seamounts, which are typically not sedimented, are also common features on the seafloor.

Other features:

6. Magma chambers - red or orange to indicate hot, molten material

7. Seamounts - brown or black to indicate basalt

For the flat layers of the cake, I used a sheet pan, cake pan, or cake round to make large, flat layers. I colored each cake according to its composition in the seafloor. For basalt, I used boxed chocolate cake. For magma, I used yellow cake with orange food coloring added to the batter, and for sediment, I used plain yellow cake batter. Seamounts and magma chambers worked best as mini cupcakes inserted into the layers of the cake. For dikes, I used Kit Kat chocolate candies inserted vertically at the spreading ridge area. After assembling all my layers, I decided to cover the cake with some chocolate icing to hide the layers for the coring activity, and then added a layer of graham cracker crumbs and chocolate rocks for effect.