Designed by architect Alfred Waterhouse, the town hall was completed in 1877. The building, facing Albert Square, contains offices and grand ceremonial rooms such as the Great Hall which is decorated with Ford Madox Brown's imposing Manchester Murals illustrating the history of the city. The entrance and Sculpture Hall contain busts and statues of influential figures including Dalton, Joule and Barbirolli. The exterior is dominated by the clock tower which rises to 87 metres (285 feet) and houses Great Abel, the clock bell.
The exterior, faced with the light brown Spinkwell stone (a hard sandstone quarried near Bradford in Yorkshire) is decorated with sculptures of important figures in Manchester's history. It was thought at the time that the dark coloured Spinkwell stone would be most likely to resist discolouration from the foul fumes of industry.
Manchester is not only one of the cradles of the Industrial Revolution, it is also the home of acid rain. It was first described here in 1852 by the pioneering chemist, Robert Angus Smith, who coined the evocative phrase. Six years later he reported how "stones and bricks crumble more rapidly due to the slow, but constant, action of the acid rain" caused by the industrial pollution of the time.
Scientists now agree that the crumbling of Britain's historic buildings has accelerated over the last few decades even though emissions from factories have greatly declined. The main culprit is thought to be pollution from car exhausts.
Weathering and erosion are often confused. Weathering is the wearing away of rocks. Erosion is the movement of the broken pieces away from the site of weathering.
Chemical Weathering
The weathering of rocks by chemicals is called chemical weathering. Rainwater is naturally slightly acidic because carbon dioxide from the air dissolves in it. Minerals in rocks may react with the rainwater, causing the rock to be weathered. Some types of rock are not easily weathered by chemicals. For example, granite and gabbro are hard rocks that are weathered only slowly. Still some of their minerals do react with the acids in rainwater to form new, weaker substances that crumble and fall away.
When fossil fuels such as coal, oil and natural gas are burned, carbon dioxide and sulphur dioxide escape into the air. These dissolve in the water in the clouds and make the rainwater more acidic than normal. When this happens, we call the rain 'acid rain'.
Acid rain makes chemical weathering happen more quickly. Buildings and statues made from rock are damaged as a result. This is worse when the rock is limestone rather than granite.
Physical Weathering
Physical weathering is caused by physical changes such as changes in temperature, freezing and thawing, and the effects of wind, rain and waves.
When a rock gets hot it expands a little, and when a rock gets cold it contracts a little. If a rock is heated and cooled many times, cracks form and pieces of rock fall away.
Wind, rain and waves can all cause weathering. The wind can blow tiny grains of sand against a rock. These wear the rock away and weather it. Rain and waves can also wear away rock over long periods of time.
Water expands slightly when it freezes into ice. If water gets into a crack in a rock and then freezes, it expands andpushes the crack further apart. When the ice melts later, water can get further into the crack. When the rock freezes again, it expands and makes the crack even bigger. This process of freezing and thawing can continue until the crack becomes so big that a piece of rock falls off.
Your Tasks at GZ
- Damage to the building stone has been caused by WWII bombs but most damage to the building is done over time. Is this long term damage caused by erosion or weathering?
- Look up at the gargoyles and statues on the front of the building. Describe what you see and explain why they have changed over time.
- Pollution from factories in Manchester is much less than it once was yet the building stone is still suffering. What is the main reason for this?
- As an optional extra post a picture of yourself and or your GPSr in front of the building as proof of your visit.
To log this cache, you will need to complete the tasks above by visiting GZ. You can use information from the cache page as well as your observations at GZ to do this. Please message us with the info (rather than post it on your log). You can log a find once we have been sent a message; there is no need to wait for a reply. We may delete your log if your answer is way off the mark or if you do not email us with your answers.