Howth that for an Arch EarthCache

A sea arch is a rock exposure that has a hole completely through it formed by the natural, selective removal of rock, leaving a relatively intact frame. 

Sea arches form when waves are deflected to the sides by a point on the headland, or where waves attack a plane of weakness which cross cuts a promontory. Where there are two different types of rock and the bottom layer of rock is softer than the top, waves can erode a plane of weakness over time to form a small crack or cave. This erosion continues on both sides and once it has worn all the way through the rock forms a small arch. The stronger rock spanning the opening at the top is known as the keystone.

Sea arches do not last very long on a geological time scale. Most collapse within a few decades to a few centuries. When the center collapses, the stacks of rocks remaining on the sides are known as sea stacks.

The coastal erosion that forms sea arches is responsible for a variety of other landforms. Caves, tunnels, columns and sea stacks are some of the landforms created by the action of waves on sections of rock that are more easily eroded than the rock around it.

Fortunately, time and conditions have lead to a beautiful hidden landscape here in Howth. Have fun as you explore within this unique part of the peninsula. Watch your step, the rocks are quite sharp and slippery. Happy EarthCaching

From promontory to sea caves to sea arch to sea stacks to rocks

To log this geocache

 Please send your answers to the following questions to me through my profile BEFORE you log your find. You don't need to wait for me to reply, I will contact you if there is a problem.

1. Apart from the sea arch what other large and prominent feature can you see here?

2. Walk through the tunnel forming the sea arch, how many of your handspans long is it?

3. Look at the keystone. Do you think it is formed of one type of rock or more than one type? 

4. Look at the diagram above. Which number stage do you think this sea arch is at?