St Michaels Mount is one of the most spectacular castles in the United Kingdom, sited on a tidal island around 400m offshore with access to the mainland at Marazion on foot by a causeway or by a ferry boat, depending on the state of the tide.
Although local people pay close attention to the tide to regulate their day to day activities or leisure plans, the concept of tides remain a source of mystery to many, especially to tourists from inland areas or landlocked countries.
Here at Marazion the tidal range – that’s the difference between High and Low water, can be as much as 5 metres! When you consider that 1 cubic metre of water weighs a ton, just imagine how many million cubic metres of water are powerfully but silently moving along our coastline every day!
The causeway to St Michaels Mount is exposed for around 2 hours either side of low water. The castle and causeway opening times are published on the St Michael’s Mount website (link below) for several months ahead, so when you’re planning a visit there’s no need to worry about whether or not you can access the Mount on foot, or whether you’ll need to take the ferry boats. Please remember, whatever the state of the tide, the Mount is always closed on Saturdays. www.stmichaelsmount.co.uk/plan-your-visit/causeway-opening-times
The Mount ferries set off from three different locations according to how high the tide is at the particular time of the day. The ferry boats start operations as soon as the causeway is covered by the rising tide. The first ferries set off from ‘Chapel Rock’ directly opposite the Godolphin Arms. In ancient times there was a chapel on this rock used by the pilgrims waiting to visit the monastery on Mount.
As the tide continues to rise, Chapel Rock also becomes an island, so the ferries move to operate from the ‘Top Tieb’ where there is a jetty allowing the boats to collect and drop off passengers. The skill of the ‘Hobblers’ (the local name for the boatmen) is very apparent here as they manoeuvre their sturdy boats in between hidden rocks all around the jetty.
As the tide rises further the ferry boat operations move a few hundred metres further east to the small harbour located at the end of Leys Lane.
Of course it’s not just the causeway that’s affected by the tide – the beach expands and contracts according to the tide providing an ever changing playground for young and old. At high tide the sea laps right up to the sea defences, whilst at low tide an expanse of golden sand and a hidden landscape of rocks and pools is revealed. At very low tides the stumps of ancient trees are sometimes exposed showing that in times gone by the area between the Mount and Marazion was a forest. Low tides and shifting sands sometimes also reveal the remains of sailing ships wrecked in the bay.
As the tide rises and floods over the causeway it’s not uncommon to see people wading through the water, sometimes up to waist deep. There is no discernible current across the causeway as it floods, so it’s not particularly hazardous, however the causeway can be slippery and indistinct as the water rises, so it’s important to take care, especially with young children.
Rock Pool Safari
During your holiday here at Marazion why not take a walk on the wild side and enjoy a rummage in the rock pools… Organised activity leaders help you discover and meet the weird and wonderful creatures that live just off the causeway. Learn amazing things about their lives and find out who is dinner and who is diner!
Rockpool Explorer is suitable for all ages but children must be accompanied. There’s no need to book, just drop in at the start time. and it’s FREE!
Sunday 9 April, 10am - 12pm
Monday 10 April, 10.30am - 12.30pm
Wednesday 12 April, 12pm - 2pm
Meet at the ‘Great Scott’ flag at the St Michaels Mount end of the causeway. Please wear rock pooling shoes or old trainers as the rocks are very slippery in crocs or flip flops. We don’t use nets but feel free to bring your buckets and sense of adventure! We don’t use nets but feel free to bring your buckets and sense of adventure!
Keep an eye on the Mount events page to see other dates planned for this popular beach activity during the year at www.stmichaelsmount.co.uk/events/rockpool-explorer
So what exactly is the tide?
For those of you interested in this complicated subject read on……. Tides are caused by the gravitational pull of the moon on the surface of the ocean which mounds up and outward in the direction of the moon. Where this mound of water has reached its highest point it is high tide. On the side of the earth opposite the moon, the centrifugal force caused by the earth’s rotation produces another mound of water and a high tide on the opposite side of the earth. Somewhere in between these two high tides are two flat areas on the surface of the ocean, these are low tides.
The moon appears to rotate around the earth each day; however it is actually the earth’s rotation that gives this appearance. The moon orbits the earth in an elliptical pattern, taking 27.3 days to complete one orbit (a lunar month). The length of time that it takes for the earth to rotate so that the moon is in the same position is 24 hours and 50 minutes, (or a tidal day).
Generally speaking, tidal cycles contain two high tides and two low tides each day and the entire tidal cycle repeats itself approximately fifty minutes later each day. So if you know that low tide is at 0800 today you can estimate that it will be at 0850 tomorrow.
The height of the tide at any point on the coastline is influenced by factors including the topography of the coast, the depth of the sea and the weather conditions. The difference between the high tide and low tide is called the ‘range of tide’. For instance, if the water depth at high tide is 6.8 metres and at low tide is 3.8metres, the range of tide is 3 metres.
There are two types of currents that you can expect in regard to tides. Flooding current is experienced when the tide is rising. Ebbing current is experienced when the tide is falling. When the tide has reached its highest and lowest points there is a brief period where there is no current
ebbing or flooding, this is referred to as slack water. In Marazion there is a current across the Causeway as the tide ebbs and flows, but it is not strong or likely to sweep you off your feet.
Two other areas that need to be covered are "spring tides" and "neap tides." It was mentioned previously that the tides are affected by both the sun and the moon. Actually, the sun’s effect is less than half that of the moon, but when these two bodies are in alignment and pulling in the same direction they cause a higher tidal range called ‘spring tides’.
On the other hand when the Sun and Moon are at right angles to one another with the moon pulling one direction and the sun pulling another there is somewhat of a cancelling effect and you get lower high tides and higher low tides called ‘neap tides’.
The largest spring tides at Marazion have a tidal range of a little over 5 metres and occur shortly after the New Moon and Full Moon closest to the equinoxes; these tides are sometimes referred to as "Equinoctial Spring Tides". The spring (or vernal) equinox occurs around 20/21 March, and the autumn equinox occurs around 22/23 September.
Neap tides occur shortly after the Moon is in its first and third Quarter, when these gravitational forces act at right angles to each other resulting in a lower than normal tidal range. Sometimes the neap tides mean that the causeway isn’t uncovered at all.
Even though tide times and heights can be predicted and are published in tide tables, the weather also affects the tides. Tide tables assume a standard pressure of 1013 millibars. A change in pressure of one millibar results in a change in the sea level by one centimetre. The effect is not, however, immediate and tends to average out over a wide area. This means that in high summer in Marazion when the pressure may exceed 1040 millibars (quite high but not abnormal) the sea level could be nearly 30 centimetres lower than tide predictions.
On the other hand, in a major storm the pressure may be only 960 millibars (the lowest pressure ever recorded in the British Isles was about 925 millibars), which would give sea levels more than half a metre above tide predictions.
As well as the atmospheric pressure, the wind also affects sea levels, particularly in Mount's Bay. Strong onshore winds cause the sea level to be higher than predicted, while offshore winds have to a lesser extent the reverse effect. Under certain conditions, a 30mph onshore wind can increase tide height by up to 25 centimetres. This effect is known as "wind set-up".
The combination of wind setup and the pressure affect associated with storms can create a pronounced increase in sea level. A long surface wave travelling with the storm depression can further exaggerate this sea level increase. This is called a storm surge. There have been such storm surges around Marazion and St Michael's Mount in recent years, causing flooding on St Michael's Mount and along the coast.
So there you have it, complicated maritime science, but hopefully a little understanding of how tides work will help you better plan your days activities on the beach and will reduce the risk of you being cut off by the tide if you go exploring.