Geology Interlude

Standard

The Isle of Wight has some fantastic geologic exposures. And since I’m in the Earth and Environmental Sciences Department, I’m going to tell you about them.

There are Cretaceous, Eocene, and Oligocene rocks on the island (there’s a disconformity where the Paleocene isn’t preserved). The rocks are all dipping towards mainland Great Britain (youngest to the north).

You can see the delineation between the beds really well on the right where the cliff is in shadow. North is to the left.

You can see the delineation between the beds really well on the right where the cliff is in shadow. North is to the left.

Sandstone and chalk are both common (some clay as well). The bay where I stayed was bordered by chalk cliffs on one side and sandstone on the other. The chalk is a slightly different age, but quite similar to the famous White Cliffs of Dover. These beds run almost the entire length of the island, so that there’s a chalk cliff a few miles from the easternmost point and the westernmost point (called the Needles) is made of the chalk itself.

The sandstone cliffs are…interesting. Sandstone weathers very easily in the presence of water. That’s why big sandstone exposures are typical of deserts, not humid areas. There aren’t any towns below the sandstone cliffs (a much wiser interaction with geology than the choices made by planners who order buildings be built on the Iowa River’s floodplain), but there are rows of less valuable beach huts where people can store things they only use during days out on the beach (and in some places with a much wider lowland, small beachside food huts or stores). Some of them are actually quite nice and even have kitchenettes where the ever present English tea can be prepared.

A sandstone cliff face. They're actually rather tall in places. There's even an elevator in one place.

A sandstone cliff face. They’re actually rather tall. There’s even an elevator in one place.

To protect the beach huts and beachgoers, people have built retaining walls along parts of the top and bottom of the cliffs and fences to keep people away from the bases. It slows down the process, but chunks still do break off from time to time.

Did you notice the missing chunk earlier (in blue)?  Or where it ended up (in purple)?

Did you notice the missing chunk earlier (in blue)? Or where it ended up (in purple)?

Up until about 6000 years ago, the island was part of the mainland. Then some big rivers changed course and scoured out valleys. And with sea level rising since the last glacial cycle, you get full separation. The rising sea level is also the reason the headlands exist–they’re basically drowned ridgelines.

To the left and center, a headland

To the left and center, a headland

The Needles used to be part of the rest of the Isle. They’re particular types of islands called ‘sea stacks’. At some point, they were all part of a headland, but wave action scoured away at the sides over time. First, they would be sea cave, then sea arches once they broke all the way through, then the arch became so big that the land above it was no longer supported and fell down, turning the part out to sea into an island.

The Needles: an excellent example of sea stacks

The Needles: an excellent example of sea stacks. Also, high-angle bedding surfaces.

//

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s