TIME DEPENDANT - MAKE SURE TO ARRIVE 2 HOURS PRIOR TO HIGH TIDE  (Parrsboro Tide Times) TO EXPERIENCE THIS PHENOMENON

This EarthCache will take you to witness the "bubbling tide" phenomenon, the only known event of its kind in the world.

Partridge Island is a significant historical, cultural and geological site located near the mouth of Parrsboro Harbour and the town of Parrsboro on the Minas Basin, in Cumberland County, Nova Scotia, Canada. 

Geology

Partridge Island stands at the edge of the ancient rift valley known as the Fundy Basin that was created when the supercontinent Pangaea began to break up about 225 million years ago. As the continental plates moved apart, they ruptured, and blocks subsided along fault lines forming the rift valleys that became sedimentary basins. The Fundy Basin is the largest of these basins in Eastern North America.

Partridge Island consists mostly of basalt from the North Mountain formation, an immense lava flow sequence that covers most of the Fundy basin. It was formed roughly at the Triassic-Jurassic boundary. The red sedimentary sandstone base of Partridge Island dates from the late Triassic period. The covering layer of dark basalt was formed from magma and lava eruptions in the Jurassic period between 175 and 208 million years ago as continental drifting further weakened the earth's crust.  

How Igneous Rocks Form

Magma Composition

Before any igneous rock can form, molten material—known as magma—must be produced. That means you must have a rock to melt in the first place to make the magma that will eventually cool to become an igneous rock. The composition of the original rock (or rocks) that melted is one of the factors that controls the composition of the igneous rock that forms once the melt cools.  Other factors are how much of the original rock actually melts, and the cooling process of the magma.

Cooling & Mineral Formation

Eventually, magma will start to rise through Earth’s lithosphere, because it’s more buoyant than its source rock. When the magma moves away from its source region, it encounters new thermal conditions, and begins to cool. As the magma cools, the temperature begins to drop beneath the melting points of different minerals. The sequence in which minerals crystallize is the opposite of the melting sequence, such that minerals with high melting points form first as the magma cools.  

Bowen’s reaction series, showing the progression of mineral crystallization as magma temperatures drop from ~1400 °C to ~500 °C. Note the corresponding names for igneous rock composition and common rock types within each compositional group.

Intrusive or Extrusive?

Magma below Earth’s surface tends to cool slowly because the surrounding rock acts as an insulator to limit how much heat can escape. Magma that stays within the Earth can take tens of thousands of years to completely crystallize, depending on the size of the magma body. Because of the long time-frame for cooling, the minerals are large enough to see without a microscope and have a phaneritic texture. Igneous rocks that form this way are intrusive igneous rocks.

In contrast, if magma reaches Earth’s surface (at which point it is referred to as lava), it is no longer insulated by the rocks around it and will cool rapidly. Any rock that forms from lava will have either an aphanitic texture due to fast cooling, or a glassy texture due to very fast cooling. Rock that forms from lava extruded onto Earth’s surface is an extrusive igneous rock.

All magmas contain gases dissolved in a solution called volatiles. As magma rises to the surface and escapes Earth’s interior the pressure on it decreases. When this happens gasses dissolved in the magma are able to come out of solution (like the fizz in an opened bottle of soda), forming gas bubbles inside it. The gas bubbles become trapped in the solidifying lava to create a vesicular texture, with the holes specifically called vesicles. This is a common texture in mafic lava flows. The type of volcanic rock with common vesicles is called scoria. An extreme version of scoria occurs when volatile-rich lava is very quickly cooled and becomes pumice. 

Scoria

Igneous Rock Names

The system for naming igneous rocks divides up rocks based on their composition (ultramafic, mafic, intermediate, or felsic), but also based on how they cooled (whether they are intrusive or extrusive). This system means that chemically identical rocks can have different appearances and different names depending on how they formed. For example, if mafic magma cools within the Earth, the resulting rock is gabbro. If it erupts and cools as a lava flow, then the rock that results is basalt. 

Common Igneous Rocks

Basalt is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% of all volcanic rock on Earth is basalt. Rapid-cooling, fine-grained basalt is chemically equivalent to slow-cooling, coarse-grained gabbro. 

Culture - Myth and legend

Partridge Island apparently got its name from a European translation of pulowech, the Mi'kmaq word for partridge. The Confederacy of Mainland Mi'kmaq report that the Mi’kmaq themselves called Partridge Island "Wa’so’q," which means “Heaven" because the island was a traditional place for gathering the sacred stone amethyst. It was also the mythic home of the grandmother of the legendary Mi'kmaq god-giant Glooscap. The natives also called Partridge Island "Glooscap's grandmother's cooking pot" because the waters around the island appear to boil twice a day when air trapped in holes in the basalt is pushed out as the tide rises.

Kluskap’s grandmother’s cooking pot

In order to log this earthcache, please send a private message to the cache owner with the answers to the following questions:

*** All sincere efforts to answer the questions and complete the tasks will be accepted.

1. [REQUIRED] In accordance with the updated guidelines from Geocaching Headquarters published in June 2019, photos are now an acceptable logging requirement and WILL BE REQUIRED TO LOG THIS CACHE.

• Post a photo in your log of yourself or a personal item with the beach in the background and clearly showing the time of your visit to prove you visited the site during the bubbling phenomenon

2. If you can get a good picture of the bubble tide please post that with your log.

3. Is the basalt that causes the bubbling phenomenon an example of intrusive or extrusive volcanic rock?

4. What are 3 differences between scoria and pumice?

5. Is the basalt that causes the bubbling phenomenon an example of scoria or pumice? Give reasons for your answer.

6. What is the difference between Gabbro and Basalt?

7. Why is the name of this Earthcache Grandmothers Cooking Pot?