A summarization of volcanic geomorphologies

Volcanic and earthquake activities have been intensified all over the world since late 1990 s.Strong earthquakes are always accompanied by volcanic eruption that may cause severe damages and disasters.To make summarization of observed volcanic geomorphology and to learn lessons from it will certainly help people preventing volcanic disasters.Observed volcanos can be classified into three groups:1.Extinct Volcanoes.Take the volcanoes of the Datong Basin, Shanxi Province, China for examples, there are low volcanic cones distributed on the basin plain among mountains.The volcanic cones usually consist of naked basalt hills with craters on top.They were mainly erupted during middle to late Pleistocene, and became extinct 90 thousand year BP.It is a kind of inland volcanic eruption constrained by fault zones.Another example is the tableshaped hills of same age, called"Fangshan"by the local people, distributed in the lower reach plain of the Changjiang River surrounding the city of Nanjing, where basalt rocks occur on the top of Cretaceous sandstone.Further to the south of China, Cenozoic volcanoes are found along the subsidence zones of the Qiongzhou Strait and the Beibu Gulf along the northern side of Hainan Island, China.They erupted during 16.77±0.47 Ma, lasted to13000 aBP, and formed a lot of low hills with craters on top.2.Dormant Volcanoes.It is a transitional type of volcanoes between the active and extinct ones.In practice, it is always hard to define.A typical example is the Mt.Kilimanjaro, located along the marginal zone, 160 km away from theeast of the East African Rift.A group of volcanoes extended for 80 km in distance from east to west with multiple craters.The last eruption happened (15~20) ×10⁴ aBP.Most of the volcanoes are extinct except the Peak of Kibo, which still releases vapor and SO₂ gas.The Mount Fuji in Japan is also a famous volcano.It started eruption in early Quaternary, and became strong in the period of 11000 to8000 aBP, with a newest eruption in1707 AD.A4 cm thick layer of volcanic ashes is widely distributed in the Tokyo area which is 100 km away from Fuji.There were 5 times of eruption during late Pleistocene to middle Holocene on the northwest coast of Hainan Island.Eruption migrated gradually from the coast to the Beibu Gulf of South China Sea, and weakened in scale.The Weizhou Island located in the Beibu Gulf is in fact a group of submerged volcanic craters, consisting of basalt and volcanic debris erupted 1.42~0.49 MaBP, and 36~33 kaBP respectively, and finally submerged under the sea 7000 aBP.3.Active Volcanoes.1) The Sakurajima of Japan.The volcano started eruption annually3000 aBP.There are over 400 times of eruption annually since 1955.The deposited volcanic debris may reach several meters thick, and many houses and huge areas of farm land are buried under the ash.Geo-disaster of mudflow may cause severe damage during heavy raining season.2) The Tianchi volcano of the Changbai Mountain in China.Records indicate that a large eruption happened 1000 years ago.Up present there still erupts SO₂.3) Datun Volcano of Taiwan Island, China.The volcano started eruption 280×10⁴ aBP.as a result of the collision between the North Luzon Arc and the Eurasian continent.The volcano ceased eruption 20×10⁴ aBP, but still active with SO₂ gas and steam escape today.4) Mount Vesuvius in Italy.It was formed25000 aBP as a volcano.A serious disaster happened in79 AD The cities of Pompeii and Stabiae were buried by thick volcanic dusts.The eruption has continued up to present, and stopped sometimes which may last for 18 months or even7 years.An observation laboratory was set up on the half way of the main peak about 678 m above the sea level to collect the data of volcanic eruption, earthquake and gravity variation.5) Located along the Pacific coast, the St.Helens Volcano, after 123 years dormancy, erupted strongly on 27, March and continued until September of 1980.A huge new crater was formed on hilly mounts, and lava flows destroyed large areas of forests, farm land, villages and even people's life!Moreover, the Mauna Loa volcano of the Hawaii Islands, 4170 m above sea level with multiple craters, and the Kilauea volcano, 1222 m high and4027 m in diameter continues to erupt lava and steam.It is famous as a natural laboratory for people to learn the processes of volcanism.6) Volcanos on the mid-ocean ridges.In Iceland, volcanic processes offer enormous geothermal energy to benefit people there.Almost half of volcanos are located under lakes or modern glacial, forming an unusual environmental nature.To summarize, we may reach the following conclusions:1.Volcanic eruption, happened along the weak parts of thinner earth crust's fracture zone, provide channels to releases energy from lower mantle.As a result, it not only changes environment natures, and brings about severe disasters, but also provide a way to avoid long time energy accumulation and collapse of large area of crust.2.Volcanic eruptions are usually regional in nature. ①.At present, lavas erupt along the mid-ocean rift to produce or expand basalt islands, such as those discovered in Iceland. ②.Volcanic eruption often happens along plate margin or adjacent areas, for examples, the West Pacific marginal seas, and edges of the Arctic plate, the Eurasian continent, and Antarctic oceanic plates.In these areas, eruption is characterized by long period of lava flow, strong debris dropping and earthquake activities. ③.Hot spot under plate is active for volcanic eruption.While the plate moving away, new volcano will continuously form upon the hot spots.As the results, a series of islands will form, such as the case of Hawaii Islands.3.Volcanic eruption is major process to create land, and even continent.4.Volcanic eruption has a nature of migration from continental margin towards mid-ocean ridge except for hot spots.5.Monitoring the active volcanism is critical important for better understanding the deep process of the earth in particular in the areas of the mid-ocean ridges, continental margins, plate boundaries and Arctic and Antarctic Oceans.