Deerpark to Herodsfoot circular walk
  1. From the parking area, make your way downhill on the main forest track to reach a barrier. Pass around this and follow the track downhill and around a hairpin bend. Continue to where a track ascends to the left.

    Old maps suggest that Deer Park Wood is on the site of Botelet deer park, which was in existence before 1540. The settlement of Botelet itself was recorded in the Domesday survey of 1086 when it included 50 acres of pasture and 60 acres of woodland. Deer Park Wood may have been part of the latter.

  2. Keep right to follow the main forest track downhill and across the bridge to where a track departs from the left.

    Meadowsweet grows on damp ground and is particularly noticeable in July from its froth of cream-coloured flowers. As the name suggests, the flowers have a pleasant scent reminiscent of almond.

    Other names include "bridewort" as it was used in wedding garlands. It was also used for potpourri and as a "strewing" herb for floors in the 16th Century to reduce smells and infections.

    The flowers of meadowsweet are sometimes used in wine, beer and vinegar, or to give jams a subtle almond flavour. One of its names - "mead wort" - likely arose as a result of it being used to flavour mead.

    Meadowsweet contains salicylic acid and has been used in anti-inflammatory herbal remedies. However when extracted into a concentrated form to make into a drug, salicylic acid was found to cause stomach upsets. It was therefore synthetically altered to reduce the level of digestive upset and then marketed as "aspirin" based on the old Latin name for meadowsweet - Spiraea.

    There are six species of the tit family of birds found in the UK but the blue, great and coal tits are the most common. Coal tits are the least colourful (grey with a black and white head). Both blue tits and great tits have green backs but great tits are larger with a black and white head, whist blue tits have a blue top to their head.

  3. Turn left and follow the track parallel to the stream until the track forks.

    Conifers can produce an economic yield of timber up to 6 times faster than broadleaf trees. Imported species such as Douglas Fir and Sitka Spruce are amongst the more common used for timber production.

    The scent of conifer trees mostly comes from volatile organic compounds known as terpenes. Two of the most well-known are limonene (which as its name suggest has a citrus scent) and pinene which advertisers describe as "pine fresh". In fact there are 2 versions of the pinene molecule with the same chemical formula but with a hydrogen atom in a slightly different place. The "alpha" version smells slightly more of pine and is soluble in alcohol and slightly in water. The "beta" version smells more of turpentine and is only soluble in hydrocarbon solvents (e.g. white spirit) so for both reasons is less useful for scented cleaning products and air fresheners than the alpha form.

  4. Keep right to stay on the upper track and follow this until it ends in a T-junction with another track.

    Bluebells are very vulnerable to trampling. The reason for this is that when their leaves emerge in the early part of the year, they are powered by the stored sugars in their bulbs. Sunlight is very limited at this time of the year and even more so in the shady places where they grow. In order to survive, they then need to photosynthesise flat-out to store enough starch in the bulb for next year's growth. If a bluebell’s leaves are crushed, it cannot photosynthesise and and doesn't have enough reserves left in its bulb to grow new ones. It's therefore important to stick to footpaths in bluebell woodland and best to take photos with a zoom lens from there as wandering around in the bluebells to take photos will inadvertently kill them.

    To support their massive weight, trees produce a biochemical compound called lignin which has a cross-linked polymer structure that makes it very rigid. Because it's so tough, most fungi and bacteria are unable to break it down. The main fungus that has worked out a way to do it is known as white rot.

  5. Turn left and follow the track downhill and over a stream to a junction where a path climbs to the right.

    Autumn colours are the result of two different chemical processes - one that gives rise to yellow leaves and one that results in red leaves. They depend differently on temperature so a cold autumn tends to produce more yellow colours whilst a mild autumn produces more red. In both cases, the length of time the colour has to develop is limited by the leaves not being blown off the tree by wind. Much of Cornwall is pretty exposed and breezy so sheltered valleys offer the best chance of good autumn colours.

  6. Turn right and follow the path uphill to a junction of paths.

    Fern fronds form in a coil (known as a crozier or fiddlehead) with the delicate tip protected in the centre. As the outer parts begin to photosynthesise, the sugars they produce cause more water to be drawn into the leaf, causing it to expand and gradually unfurl.

    The trees planted alongside the path are Northern Red Oak, native to North America. The large leaves can turn a spectacular red colour in autumn if the conditions are right.

  7. Turn left and follow the path to reach a junction of paths with a small triangular grassy island.

    If you have secateurs, give any brambles or gorse encroaching into this path a snip back on your way through. As the trees have been felled and replanted, the path here needs help from walkers to keep it clear until the young trees can get established which will then block out the sunlight from the undergrowth.

  8. When you reach the junction of paths, turn right and follow the path around the barrier. Keep left through the parking area to meet the lane.

    Robins are also able to see magnetic fields. Receptors in their eyes make magnetic fields appear as patterns of light or colour which allows them to use the Earth's magnetic field for navigation. They only seem to use their right eye for this as the left half of their brain (linked to the right eye) does the processing.

  9. Turn left onto the lane and follow it a short distance to where a tarmacked track departs to the right alongside a terrace of 3 small cottages.
  10. Bear right onto the track and follow this downhill to where an unsurfaced track with a wooden barrier departs to the left.

    By the end of the First World War, Britain had only 5% of its original forest cover left. The Forestry Commission was founded in 1919 to address the timber shortage and bought large amounts of agricultural land, becoming the largest landowner in Britain. As part of the 1968 Countryside Act, the public have been allowed to use many parts of the forestry estate for recreation. Now known as Forestry England, it still plays a key role in woodland creation as part of the government's strategy to increase Britain's tree cover to 12% by 2060.

  11. Bear left onto the unsurfaced track and pass around the barrier. Follow the track to a junction where a smaller path departs to the left from a hairpin bend.
  12. Turn right to follow the main track around the hairpin bend and continue until it ends in a T-junction.

    Around 400 million years ago, green algae made its way from the sea to the land and the first liverworts appeared. These ancient, very simple plants are still around today. DNA studies suggest that all land plants and mosses may have originally evolved from early liverworts.

    Liverworts are found in damp, shady places but form flat structures that almost resemble soft corals. Their name is based on the appearance of the leaves which was thought to resemble an animal liver. Like mosses, liverworts don't produce flowers but instead reproduce via spores.

  13. Turn right and walk a few paces to a path departing from a post on the opposite side of the track (with a purple Riverside Walk sign). Turn left to follow this path over the footbridge.

    The stream is a tributary of the West Looe River. The confluence with the main river is in Herodsfoot.

    The West Looe river rises near Dobwalls and runs for roughly 8 miles through Herodsfoot and Churchbridge before entering the creeks of the flooded river valley just below Milcombe with a final mile along the creek to its confluence with the East Looe river. The sedimentary rocks surrounding the river form an aquifer reserve which results in the river levels being topped up by groundwater during periods of low rainfall.

  14. Once over the bridge, follow the main path around a bend to the right (indicated by the next purple arrow). Continue until the path emerges in a turning area near some cabins.
  15. Walk through the turning area and join the tarmacked lane. Follow this to a junction.

    The woods at Herodsfoot had a history of charcoal burning. Since this was one of the three ingredients needed for gunpowder and woodland provided a shock-absorbing environment in the event of explosions, work began on the construction of gunpowder works in 1845. The East Cornwall Gunpowder Company was founded, funded by the Quaker community, and the site was managed by the family who had run the charcoal business. Thanks to demand from the nearby mines, the business was so successful that a sister site was set up near Liskeard in woodland in the Glynn valley. This took its name from the name of the wood where it was located so it was known as Trago Mills.

  16. Turn right at the junction and follow the lane downhill to another junction. Bear left and continue a short distance to reach a tree with a "Beech" sign pinned to it, just after the parking areas marked 4 and 5.

    The Herodsfoot gunpowder mill was destroyed twice by explosions in the 1850s.

    In May 1950, an explosion killed two men and flattened most of the site. The explosion was described in a newspaper as "grand but awful evidence of the tremendous power of gunpowder…a spectacle of devastation and wreck such as our readers will be totally unable to conjure up in their imaginations." Despite this, the mill was rebuilt and resumed operation.

    In October 1857, another explosion destroyed the mill again, killing four workers. The shock wave was felt in Liskeard and Lostwithiel. Once again the mill was rebuilt.

  17. Bear left onto the small path leading gradually uphill just after the tree. Follow the path through the woods to eventually reach a stile. Cross this and continue to reach another stile (this time into a small meadow).

    In May 1876, a workman was working on a wooden structure with a mallet but a small piece of grit on the wood caused a spark which unfortunately landed on some gunpowder. The fire spread to an incorporating mill (where the ingredients are ground together into a powder) which exploded, causing a chain reaction of explosions across the site which damaged or completely destroyed almost every building on the site and killed two men. The mill was rebuilt and continued operating until the 1960s when one more explosion finished it off.

  18. Cross the stile and walk along the length of the meadow to a gate in the top corner at the far end.

    If there are sheep in the field and you have a dog, make sure it's securely on its lead (sheep are prone to panic and injuring themselves even if a dog is just being inquisitive). If the sheep start bleating, this means they are scared and they are liable to panic.

    If there are pregnant sheep in the field, be particularly sensitive as a scare can cause a miscarriage. If there are sheep in the field with lambs, avoid approaching them closely, making loud noises or walking between a lamb and its mother, as you may provoke the mother to defend her young.

    Sheep may look cute but if provoked they can cause serious injury (hence the verb "to ram"). Generally, the best plan is to walk quietly along the hedges and they will move away or ignore you.

  19. Go through the gate and bear right for a couple of paces to reach a lane. Turn right onto the lane and follow this downhill until it ends in a T-junction.

    The remains of two engine houses are situated at the bottom of the field on the right (on private land).

    Herodsfoot Mine was a lead and silver mine started as early as the 17th Century, initially using waterwheels for power and retrofitted with steam engines in the 19th Century.

    There are remains of 19th Century pumping and winding engine houses in the valley situated near one mineshaft. Another mineshaft is located next to the driveway to Tresarren Farm.

    A second mine (known as Herodsfoot Mine, and the original was then known as North Herodsfoot) was set up nearby in the 1850s and this took over as the main operation as it was more profitable.

  20. Turn right onto the lane and follow this past the telephone box to a junction.

    Herodsfoot was originally just called Heriad which is from the Cornish words hyr-yard and means "long-ridge" (Herodshead was similarly Bronhiriard - "long-ridge hill"). The long ridge is likely to be a reference to the spur of land between the East and West Looe rivers. The name gradually changed from Heriad so that by the 17th Century it had become Heriod and then in the 18th Century it became Herod. The post-mediaeval English-speaking population also added the "foot" to give the meaning "foot of the stream at Heriad" (as they didn't know the name meant an upland location in Cornish).

  21. Keep right at the junction to follow the lane uphill past Tresarren Farm. Continue as the lane levels out until you pass an obvious entrance into the woodland on the right and then a short distance further to reach a smaller path leading into the woods on the left (both fenced with wooden rails).

    Primrose seeds are quite large and therefore, due to their weight, don't travel far from the plant. This causes a clump of primroses to spread out very slowly over time and means it takes a long time for primroses to colonise new areas. This makes large carpets of primroses a very good indicator of ancient woodland where they would have had many hundreds of years to spread out.

    Bastard balm is a native plant found on the edge of woodland with pretty orchid-like flowers of white with a pink "tongue". It was once common but has become increasingly rare in Britain as woodland coppicing has been replaced with modern forestry management. Bastard balm still has a last stronghold in Devon and Cornwall. It's related to lemon balm and the name is thought to be a rather harsh statement about the lack of lemon flavour.

    From April to June, white flowers of Greater Stitchwort can be seen along hedgerows and paths. The petals are quite distinctive as each one is split almost all the way to create pairs - most of the flowers typically have 5 pairs.

    The font now in a garden in Herodsfoot is from a mediaeval chapel in St Winnow parish dedicated to St Martin. In fact, there were 2 chapels in St Winnow both dedicated to St Martin. It was generally thought that the font was from the chapel at Respryn but it's been suggested it may have come from the other chapel at Bosmaugan instead.

  22. Turn left and follow the path downhill past one junction to a second junction of paths (where you emerged earlier on the walk).

    Birds are technically considered reptiles and the only surviving group of dinosaurs as they are the descendants of the group known as theropods (that Tyrannosaurus rex belonged to). The oldest bird fossils are about 150 million years old and looked like small, feathered dinosaurs with sharp teeth.

  23. Bear right to follow the path you followed earlier on the walk to a junction with a small triangular island of grass.

    Rosebay willowherb is a tall plant with a spike of pink flowers in late summer which can often be seen beside paths and tracks. Their long leaves have a distinctive thin, white vein along the centre.

    It is a pioneer species which is good at colonising disturbed ground as its seeds travel long distances in the wind and remain viable in the soil for many years. It was considered a rare species in Britain in the 18th century but spread along the corridors cleared for railways in Victorian times.

  24. This time, keep left at the junction and follow the path to reach a junction of four paths.

    Many hoverflies have colour patterns that mimic stinging bees and wasps so predators avoid them even though they don't sting. They are quite convincing con-artists and when caught will push down their abdomen in a simulated stinging action to keep up the illusion.

  25. Turn right and follow the path uphill to return to the parking area.

    Squirrels assess each of their acorns before burying them. If an acorn is too light (which suggests it might have a hole), the squirrel will eat it immediately rather than risking it going mouldy.

Holly is able to adapt to a range of conditions but prefers moist ground. It is very tolerant of shade and can grow as a thicket of bushes underneath larger trees. However, given the right conditions, holly trees can grow up to 80ft tall!

Holly was known in Cornwall as the holm (bush) and is the origin of the Holmbush area of St Austell and Holmbush Mine in Kelly Bray.

The berries of holly contain a chemical compound very similar to caffeine. Only in very small doses is this a stimulant; in larger doses it is toxic. It is for this reason that you see holly berries on bushes rather than being inside the nearest bird. The birds have learned to wait until after the frosts have reduced the toxicity of the berries before eating them.

Anyone who has sat on a holly leaf will know how prickly they can be but the leaves particularly on larger holly bushes often vary considerably with less spiky leaves nearer the top.

Holly is able to vary its leaf shape in response to its environment through a chemical process known as DNA methylation which can be used to switch genes on and off. If its leaves are eaten by grazing animals or trampled by walkers, the holly will crank up the methylation level to produce really spiky leaves on these stems. Conversely on the stems where the leaves are able to grow old in peace, the holly will produce versions that are flatter and therefore more efficient at catching the light. An individual leaf can last up to five years.

Holly has separate male and female plants, so not all holly bushes produce berries - only female plants. In less biologically-enlightened Pagan times, holly was thought to be a male plant (the spikes symbolising aggression) whereas ivy was regarded as a female plant (symbolising attachment). The Christmas Carol "The Holly and the Ivy" is thought originally to derive from Pagan fertility myths onto which Christian symbolism has subsequently been added.

The association of holly with winter celebrations predates Christianity: druids were known to use holly wreaths which, it is likely with some discomfort, they wore on their heads.

From Roman times, holly trees were planted near houses as it was believed to offer protection from witchcraft and lightning strikes. There is some scientific basis for the latter at least: the spines on the leaves can act as lightning conductors. The sharp points allow electrical charge to concentrate, increasing its potential to form a spark.

Bracken is a type of fern. Perhaps the easiest way to spot mature bracken plants is by their sturdy stem which acts a bit like the trunk of a tree with leaves going out horizontally from this. Other ferns leaves tend to grow directly out of the ground. Earlier in the year, bracken is recognisable by the fronds emerging from the ground singly rather than grouped in tufts.

Although the fronds of bracken die back each year, the black underground roots are perennial and spread extensively, sending up fronds at intervals. The root system of one bracken plant can stretch up to a quarter of a mile across making bracken one of the largest plants in the world.

Fossil records indicate that bracken dates back at least 55 million years. By 24 million years ago it had a worldwide distribution and it is now thought to be the most common plant in the world.

Bracken is both poisonous and carcinogenic to many grazing animals which will avoid it if at all possible. Eating bracken is not recommended as it is thought that the carcinogenic properties may also apply to humans based on the circumstantial evidence that Japan, where young bracken fronds are a delicacy, has the highest levels of stomach cancer in the world.

Bracken releases toxins into the soil which inhibit the growth of other plants, and the shade created by its large leaves and its thick leaf litter also makes it hard for other plants to compete. This and avoidance by grazing animals makes it quite difficult to control, particularly in steep areas where mechanised cutting or ploughing is difficult. Treading by livestock can reduce bracken's competitive advantage, particularly during winter when frost can attack the roots.

In woodland, the Victorians used a horse-drawn roller to control bracken. The hollow roller was made from a frame of iron bars which crush bracken stems but allow springy tree saplings to ping back. This horse-drawn method still survives in Cornwall and is sometimes hired by the National Trust for their woodlands.

Bracken has been used as a fuel for centuries but is of interest as a modern biofuel due to its very high calorific value. Normal firewood produces around 15-19 gigajoules of heat per tonne of material (depending on moisture content - drier is more efficient hence kiln-dried logs). Elephant grass can produce around 18 GJ/t and bracken can deliver 21 GJ/t. At least one company has piloted creating compressed fuel briquettes from bracken in a similar way to elephant grass.

Foxgloves have a life cycle which spans two years. The seeds germinate in spring and during their first year they produce a "rosette" of large, velvety green leaves with toothed edges. These are particularly noticeable from October onwards once other vegetation has died back. The leafy foxglove plants remain dormant throughout the winter, ready for a quick start in the spring.

In spring, whilst foxgloves seeds are germinating, the established foxglove plants from the previous year start producing their characteristic flower spike. Once these have been fertilised and the seeds have been produced then the plant dies. One foxglove plant can produce over 2 million seeds.

Foxgloves are reliant on bumblebees for pollination and bumblebees are much more active when the weather is good. Partly, as an insurance policy against bad weather, foxgloves have evolved to stagger their flowering over several weeks, starting with the flowers at the base of the stalk and working up to the top, where the higher flowers protrude over other vegetation that has grown up in that time.

The male and female parts of a foxglove flower mature at different times to help avoid self-fertilisation. This also ties in with the flowers maturing at the bottom of the spike first as pollinators often start at the lowest flower and then work upwards. They land on the mature female flowers first with a cargo of pollen from another plant, and then leave via the mature male flowers with a new load of pollen.

Although nearly all foxgloves are purple, a fairly rare white form does occur and an even more rare pink form sometimes occurs along with this.

As well as attracting insects, the brightly coloured foxglove flowers serve as a warning for animals that the plants contain toxins. All parts of the plant can cause a range of ill-effects in humans from nausea to heart and kidney problems which can be fatal.

The common name "foxglove" dates back many hundreds of years but the origin is unknown. The "gloves" almost certainly refers to the shape of the flowers, and the Latin name Digitalis (finger-like) is along similar lines. The curious part is the "fox" and many different suggestions have been made as to where it came from. It is possible that it is a corruption of another word. One suggestion is "folks" which was once used to mean "fairies".

Mosses are close relatives of the first plants to colonise the land 500 million years ago. They descended originally from freshwater algae but evolved an outer coating that protected them from the temperature changes and UV radiation that made life on the land more of a challenge than in the water. There are now estimated to be over 10,000 species of moss.

Mosses reproduce with tiny spores rather than seeds. Many mosses use wind to carry their spores and produce tiny stalks with the spore-releasing equipment on the top in order to catch the wind - these can be seen as thread-like structures standing up from the moss. These spore-releasing devices often have a ring of teeth around the edge (visible with a magnifying glass) to control the release of the spores, allowing them to be released gradually over a period of time to catch gusts of wind of different speeds and in different directions.

Sphagnum (peat) mosses use compressed air to launch their spores. To get an idea of the acceleration that the spores are launched with, an astronaut in a rocket launch experiences an acceleration g-force of about 3 g and the maximum in a fighter jet is about 9 g. Sphagnum moss spores are accelerated at 36,000 g!

Mosses don't have roots but instead have little rootlets known as rhizoids. Since there is no need to root into soil, mosses can grow on stones, tree trunks, buildings etc. This together with their wind-carried spores makes them excellent colonisers of barren land. The buildup of organic material from dead moss then provides an environment that other small plants can start to colonise.

Mosses' lack of deep roots mean they need to store their own supply of water during dry periods which is why they are found in shady places that are not dried-out by the sun. This also applies to moss on trees - it rarely grows on the south-facing part of the trunk which can be used as a crude form of compass when navigating.

Some mosses are able to absorb 20-30 times their own weight in liquid. Moss was used in several ancient cultures as nappies: babies were carried in a moss-lined bag to prevent leaks. Moss has also traditionally been used to line hanging baskets which are very prone to drying-out. Areas of moss help to protect soil from erosion by runoff and rivers from sediment and flooding by capturing rainfall and giving it chance to soak slowly into the soil.

The massive gain in efficiency by breaking rocks with explosives rather than hand tools resulted in increased profits for the mine owners but it was less good for the miners themselves. When gunpowder burns, it produces copious amounts of acidic sulphurous gasses which attack the respiratory system - far from ideal in the poorly-ventilated confined space of a mine. A quill or reed filled with gunpowder was used as a fuse which worked most of the time but burnt at an unpredictable rate, and burning material from the fuse could drop and prematurely ignite the main body of gunpowder. Consequently there were many horrific accidents and fatalities.

German miners (whose traditional outfits now appear on garden gnomes) introduced the use of gunpowder for mine blasting in Cornwall in 1689 (as well as gnomes). This was first carried out in one of the mines of the Godolphin estate, quite possibly Great Work Mine.

Gunpowder represented a great technological breakthrough, as beforehand, rocks had to be cracked by heating and rapid cooling, or by soaking wooden wedges in water. An amount of granite that would take 6 days of work to break with a pick could be broken in one blast.

The reason that mills were required for gunpowder manufacture is that the finer the particles of the three ingredients, the more explosive the mixture. An ultra-fine dry dust would be far too dangerous both to manufacture or use so the ingredients were ground down into a fine paste using water. The paste was then broken into granules before being dried out. Any dust was removed from the granules as it would have been disastrous to have suspended particles of gunpowder within the air of a mine where metal tools and candles were being used. Finally, the dried granules were coated in graphite to make them flow more easily and also more water-resistant.

Gunpowder was imported into Cornwall until 1808 when the first Cornish gunpowder factory opened at Cosawes Wood, Perranarworthal, about 5 miles from Falmouth, followed by another at nearby Kennall Vale in 1813. By 1836, the consumption of this was considerable with 30 tonnes being used in Cornish mines. By the 1860s the three largest mills were in Kennall Vale, Herodsfoot and the infamous Trago Mills.

Secluded river valleys were chosen as the sites for gunpowder mills for their distance from population, shielding provided by trees and the availability of water power. In the event of an explosion, the trees also shielded the process buildings and storage magazines from one another, reducing the chance of a chain reaction. The roofs of the buildings were also designed to blow off relatively easily so the force from the explosion (and any fragments of occupants) would be vented upwards, minimising the damage to the building.

Gunpowder was discovered by accident by Chinese Alchemists attempting to make an elixir of life to render themselves immortal. A text from the 9th Century documented the event which quite literally backfired:

smoke and flames result, so that their hands and faces have been burnt, and even the whole house where they were working burned down.

Lead was one of the earliest metals discovered by the human race and was already in use by the start of the Bronze Age - in fact part of the "Stone Age" probably should be called the "Lead Age". Not only was it abundant and relatively easy to extract, it was extremely versatile, being easily molten, moulded and was corrosion resistant.

Lead's major downside was discovered quite quickly - lead poisoning was well known about by Roman times. Nevertheless, lead's usefulness outweighed any scruples, particularly in times when there were lots of other things to die from.

The ancient Romans used lead for making water pipes and this continued until 1970. In hard water areas, limescale soon lined the pipes, preventing lead dissolving into the water. However, areas with acidic soils, such as Cornwall, would have been much more prone to lead poisoning from water pipes.

Since the 1970s, the use of lead has stopped for water pipes, paints, fuel additives and solder. By 2016, over half of the lead still produced was used for batteries, mostly for cars, and this is now in decline as new battery technologies are being developed.

The lead ore found in Cornwall is a form of lead sulphide known as galena which often contains an appreciable amount of silver. This was first smelted to produce "argentiferous lead" and then the silver was separated by a process known as "cupellation". The molten alloy of the 2 metals was placed in an oxygen rich furnace which caused the lead, but not the silver, to oxidise. The lead oxide was then absorbed into a calcium-rich material such as the ash from bones or seashells, leaving the liquid metal silver on the surface of the "cake". The lead oxide could later be converted back into lead by smelting it with charcoal.

You may remember from school geography lessons that the faster-flowing water around the outside of the bend causes a meander in a river to slowly grow as the outside edge is eroded and sediment is deposited on the inside by slower-moving water. At this point, your school geography teacher probably got excited about ox-bow lakes and never got around to explaining exactly why the water flows faster on the outside in the first place. So that you don't go to your grave feeling short-changed, an attempt at an explanation follows...

Flowing water piles into the outside of the bend and creates a higher pressure there. Close to the riverbed, water is moving very slowly so the high pressure pushes water across the bottom from the outside to the inside. This drags the faster-moving water across the top of the river to the outside to take its place. This spiralling current both erodes the outside edge with faster-moving water and also transports the sediment back across the bottom to the inside