Mud of the Earth: Composition, Mudflows, and Uses
A Friend and a Foe
Mud is a slimy or sticky mixture of soil or other fine-grained earth material and water. It's often a suprisingly useful material. Animals use mud to build shelters, obtain nutrients, and protect their bodies. Children often enjoy playing with and in mud. In some places, humans build their homes from the material. Some people apply mud packs to their body for the purported health or beauty benefits.
Mud is not always so benign, however. It can make surfaces slippery and dangerous for travellers. A large and rapid flow of the material can destroy life and property. In Indonesia, the Lusi mud volcano has been erupting since 2006 and has destroyed life and villages. Scientists predict that it will continue to erupt for twenty-five years or more.
Composition of Mud
Mud is often produced from a mixture of soil and water. The term "mud" isn't used unless the mixture is significantly thicker than pure water and has a slimy or sticky consistency, as shown in the photo above. The consistency depends on the contents of the soil as well as the amount of water that's been added.
According to the University of Hawaii, a typical soil contains 45% minerals, 25% water, 25% air, and 5% organic matter. The minerals consist of sand, silt, and clay, which differ in particle size. Sand has the biggest particles (2.00 mm to 0.05 mm), clay has the smallest (less than 0.002 mm), and silt particles fit in the middle with respect to size. The clay particles produce the sticky consistency in mud. The higher the clay content, the stickier the mud. Gumbo soil has such a high content of clay that it becomes sticky with very little addition of water.
Mud runs are becoming popular events in some places. There are risks to participating in one of these events, however. Mud is slippery. In addition, there is a danger of infection from mud that enters wounds, the eyes, or entrances to the body. This is especially true if the mud is contaminated with animal dung or urine or human body fluids.
A Mudflow in British Columbia (Raw Video)
Mudflows and Mudslides
Since mud has a higher liquid content than soil, it has a tendency to move under certain conditions. The term "mudflow" refers to this movement, as defined by the United States Geological Survey below. The organization says that the term "mudslide" for a downhill movement of mud is not technically correct, though it's often used by the media. It's used by some insurance companies, too. A homeowner should check how their company defines the terms and make sure that their policy covers damage from both mudflows and mudslides if these terms refer to different processes in the policy.
Mudflow: a general term for a mass-movement landform and process characterized by a flowing mass of fine-grained earth material with a high degree of fluidity.— USGS (United States Geological Survey)
A Dramatic View of the Lusi Mud Volcano and Mudflow
The Lusi, Sidoarjo, or Lapindo Mud Volcano
The Lusi mud volcano has been characterized as "the world's most destructive mud volcano". The name Lusi is a contraction of two words—lumpur, which is the Indonesian word for mud, and Sidoarjo, the city on the island of Java near where the eruption is occurring. The eruption is also known as the Sidoarjo or the Lapindo mud volcano.
The eruption began on May 29th, 2006, and killed thirteen people. The deaths were due to an explosion of an underground gas pipeline. The explosion is thought to have been triggered by the eruption. The mudflow has destroyed whole villages, including schools, mosques, businesses, and the dwellings of many thousands of people. The number of people reported to have lost their homes varies according to different sources, but it's between 40,000 and 60,000. The mud deposited by the eruption is up to 40 metres thick.
Mud is still flowing from the volcano today, though at a reduced rate. Scientists say that it will continue to erupt for many years to come. The mud consists mainly of a mixture of clay particles and water.
An Aerial View of the Mudflow
Cause of the Eruption
The cause of the mud eruption is unknown. Two theories attempt to explain the event. One involves a natural cause. On May 27th, 2006—just two days before the eruption— an earthquake with a magnitude of 6.3 on the Richter scale occurred 260 km away. According to the theory, vibrations from the earthquake liquified underground mud, forcing it to rise under pressure. The mud is located in the Kalibeng Formation, a notable feature of Java's geology that is rich in clay. Some researchers think that the earthquake was located too far away and was too weak to have much of an effect, however.
The second theory puts the blame for the eruption on humans. A gas exploration well was being drilled just 200 metres away from the site of the mud eruption. The well was 2,834 metres deep. Unlike the first section of the well, the last 1,743 metres weren't surrounded by a steel and cement casing at the time of the eruption. According to the theory, water from the bedrock flowed towards the bottom section of the well with such a high pressure that it created cracks in rocks or made existing fault lines bigger. As it flowed, it met the mud in the Kalibeng Formation, forcing it up to the surface through a fault line.
As the time of the eruption's first appearance retreats further into the past, it's becoming less likely that researchers will identify the cause of the event. Understanding the reason for the eruption might help us to better understand natural processes in the Earth or the ways in which we affect them.
Effects of the Eruption
Life is said to be financially hard for many of the people displaced by the mudflow. Some have finally received compensation after many years of wrangling by the powers-that-be. The gas company has denied any responsibility for the eruption and says that the earthquake was responsible for the event. The government has now become financially involved in the compensation.
According to one report (referenced below), many of the affected people have used the money to pay off the huge debts required to set up a new life and haven't become rich from the compensation. Some earn a small amount of money by acting as tour guides for the mudflow.
Some of the mud around the main vent has sufficiently hardened that it can now be walked on. Smaller vents have appeared. Tourists visit the area to walk on the mud and take photos. Statues of people partially submerged in the mud are a poignant reminder of disrupted lives. (The statues can be seen at the end of the first Lusi mud volcano video in this article.) Sights of protruding roofs and mud spurts from the ground attract visitors.
A university study has found that the mud entering rivers contains heavy metals, which could be affecting people far away from the eruption site. Fish caught for food may be absorbing the metals, as they have done in other polluted areas. This in turn could affect the health of people who eat them.
Animals That Use Mud
Many animals make use of mud in some way. They live in it, catch their prey on it, build their home with it, or coat themselves with it for protection of some kind. Some specific examples of how animals use the material are described below.
- Elephants appear to love wallowing in semi-liquid mud, which cools them down. The mud coats their skin and acts as a sunscreen. The coating also provides protection from biting insects.
- Some butterflies engage in a behaviour called mud-puddling. They land on mud (or another moist substance such as fresh dung) and drink fluid in order to absorb its minerals and perhaps other nutrients. The insects sometimes gather on mud in a group. Males appear to mud-muddle more than females.
- Mudflats or tidal fats are flat areas of mud deposited by the tide of the ocean or by a river. They are home to many burrowing animals, including worms, clams, and crabs. The animals breathe through a tube extending to the surface of the mud.
- Although mudskippers are fish, they are able to obtain oxygen and move on land and spend much of their time there. They not only build a burrow in the mud but also move over it to catch their prey, which includes worms and crustaceans.
- Mud dauber is the general name for multiple species of solitary wasps that build their nests from mud. The female collects the mud with her mandibles.
- The barn swallow is an example of a bird that builds nests made from mud. It comes to the ground to gather mud and grass for the nest construction. The bird almost always builds its nest on structures created by humans.
Mud Homes for Humans
In certain countries and cultures, some human homes are made of mud. A related structure is a cob house, though this isn't made of pure mud. The building material for a cob house consists of soil, clay, straw, and water.
One thing that has occurred to me and probably to many other people is whether human dwellings made of mud can withstand rain. From what I've read, a mud building can often withstand light rain following by a drying out period but not a heavy or continuous downpour unless it's protected in some way.
Some mud buildings have existed for hundreds of years, so the material can obviously be resilient in the right climate and circumstances. The proportions of different minerals in the mud as well as any other materials in the bricks, such as straw, play a role in building resilience. So does the way in which the bricks are dried. Some modern mud buildings have a foundation and/or deep, overhanging eaves made of another material to protect the walls. Another aid that's used is to add a little bit of concrete to the bricks (where it's available).
The ways in which humans and animals use mud are interesting. The material has a dark side, however. The destructive power of anything other than a minor mudflow should never be underestimated.
- Soil composition information from the University of Hawaii at Manoa
- Facts about the Lusi mud volcano and mudflow from The Conversation
- Life for the Lusi mud volcano survivers from the phys.org news service
- Elephants wallow in mud from the Oregon Zoo
- Butterly mud-puddling from the Central Sierra Environmental Resource Center
- Information about mudskippers from the Two Oceans Aquarium
- Black and yellow mud dauber information from the University of Florida
- Barn swallow facts from the Cornell Lab of Ornithology
- Information about building mud brick homes from the Australian government
Questions & Answers
© 2017 Linda Crampton