QUESTION NO 25. GE140

 Volcano is the part of the Earth that erupt magma from the Earth’s chambers. The magma upon reaching the surface transforms into  ash, lava and volcanic gases. Over a long period of time with many such eruption a volcano is formed layer by layer until the magma in the chamber beneath is erupted. Also there are different features which formed due to volcanoes like composite volcano, ash and cinder cone, shield volcanoes plug domes, crater and caldera.

Shield volcano according to David A. William and Jan Redebaugh(2022), Are formed from effusive eruptions tha produce relatively low-viscosity lava flows forming of dume-like shape by the accumulation of thousands of layers of lava flows.

Oregen state  University(2003), Explained that shield volcano es are usually constructed almost entirely of basaltic and andesitic lava flows which were very fluid when erupted. They are built by repeated eruption of that occured intermedietly over vast period of time.

Also Walker(2000) Explained that shield volcanoes are formed when a centralized vent produces low viscosity   flows of lava and sread out in a wide area creating a broad, gentle sloping shape over a long period of time.

Generally shield volcano is a type of volcanic cone that is broad and gentle sloping with a shape resembling a worrior’s  shield. The shield is formed from a numerous fluid lava flows that spread out in all direction from the central vent. Shield volcanoes are typically composed of basaltic lava and have low silica content allowing the lava to flow easily. Some famous examples of shield volcanoes includes; Mauna Loa in Hawaii, wolf volcano in Galapagos Icelands, Nyamuna Gina in the Democratic Republic of Congo and Olympus Mons in Mars. The following are the characteristics of shield volcanoes;

1.The volcanoes are composed of basaltic magma which is high in tempereture, very low on silica and gas content, This means that through the presence of tempereture to be high and also the low amount of silica lead to make that magma which erupted outside the Earth surface to be inform of the liquid that can not be easily to be soldified when researched on the surface due to presence of high tempereture so, Through this tends to make the lava to spread far away rather than other features. So, Shield volcanoes are composed of basaltic magma due to the high temperature and low silica .

2.The lava erupted from the shield volcanoes are runny and non-acidic; This means that  through lava to be inform of liquid tends to runny far away, This is due to the absence of acid which can make a lava to be cooled and soldified easily so, Runny and non-acidic of the shield volcanoes , is among of the characteristics of the shield volcanoes.

3.It has a gentle slopes, Shield volcanoes have a low, broad shape with a gentle slope of about 5-10 degrees. They have a fluid lava flows, Shield volcanoes erupt fluid lava that spreads out in all directions, Creating  a broad shield-like shape.It has infrequent explosive eruptions, shield volcano generally have infrequent explosive eruptions and are not as explosive as sratovolcanoes but they can still pose a hazard to nearby communities due to the risk of lav flows. They lacks a central crater, unlike stratovolcanoes, Shield volcanoes lack a central crater and instead  have a broad summit area. Shield volcanoes are known also for producing Hawaiian-style eruption, Which are characterized by the emission of slow moving lava flows. Volcanoes are widely and recognized and studied type of volcanic landform, With different perspectives from geologists, Volcanologists and Earth scientists.

4.it is less violents.

5.short time between eruptions.

6.lava flows long distance before cooling.

See the diagrama(1:1)  below showing a shield volcanoes;

            1:1. A shield volcanoes

Composite volcanoes according to Sanjeel Kumar(2022), Explained as the type of volcano which exclude lava of intermediate silica content and medium to high viscosity known as andesite.

according to Pratic Santro(2020), Composite volcano is a conical volcano consisting of layers of solid lava flows mixed with layers of other volcanic rocks and with a steep-sided volcanocomposed of altenating layers of ash and lava, often with a creater at summit.

According to the internation Association of Volcanology and chemistry of the Earth's interior, Composite volcano is a steep sided volcano composed of explosive and effusive eruption of basic to intermediate magmas.

Generally composite volcano also known as stratovolcano are large, steep-sided volcanoes that are built up of altenating layers of ash, lava and volcanic rocks. Those volcanoes normally are active within a long period of time ten to hundreds of thousands of years and erupt periodically.A classic composite volcano is conical with a concave shape that is steeper near the top. These mountains commonly have snow-covered peaks standing high above the surounding mountainous terrain. The ccomposite volcanoes like those found along the pacific "Ring of fire" are usually found along the subduction zone. Examples kilimanjaro, Meru, Nyirangongo in Zaire and muhavuna composite cone in the east of virungo rangers.These definitions emphasize the key features of composite volcanoes, the following  are the characteristics of composite volcanoes.

1.Composite volcanoes have lava and ash deposite; Lava of intermediate silica and medium to high viscosity known as andesite are excluded. Ash is amixture of particles varying from tiny dust to large rock fragment so, Composite volcano produce both lava flows and ash deposits, Which build up over time to form a steep-sided cone shape.

2.Composite volcanoes have diverse range of eruption; Composite volcanoes can produce a wide range of eruption styles, Including explosive eruptions, Effusive eruptions and lava dome eruptions.The composite volcanoes are domant over a long period of time as they erupt, Lava and ash flow down the sides of the volcano at the speed of Avallanche.

3.Composite volcanoes have steep slopes, composite volcanoes have a steep cone shape, With slopes ranging from 30-40 degrees. have explosive eruptions, Composite  volcanoes are known for their explosive eruptions Which which result in the emission of ash, pumice and volcanic rocks. Have central crater composite volcanoes typically have a central crater at the summit, from which ash, pumice and lava can be erupted. Also composite volcanoes have common location, composite volcanoes are commonly found along tectonic plates boundaries, particularly at subduction zones where one plates is forced beneath another.

4.it is more violent.

5. Long time between eruption.

6.lava flows short distance due to its viscosity

The diagram (1:2) below showing  composite volcanoes;

Generally both composite volcanoes and shield volcanoes have more significances to the environment as well as in economic, socially and culturally levels in the development as shown as follow respectively; Are the source of tourism attraction, are the source of hills formation, are the source of minerals, are the source of soil fertility and are the source of employment to the people who are surrounding that areas and other people.

                REFERENCES

David A  William and Jan Redebaugh(2022), Chronology and dynamics of a large silicic magnetic system. Central Taupo volcanic zone,New Zealand Geology.

Oregon state University(2003), From surfetyan to an energetic maar eruption. J. volcanol Geothemal Res.

Patrick Santro(2020), Srombelian explosive style and source conditions; insight thermal(FLIR) video bull volcanol.

Walker(2000), Explosive volcanic eruptions, A new classification scheme.