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배주은쌤의 토플배경지식
학원명 : YBM 강남

게시일 : 2020.02.05

[강남YBM토플] 배주은쌤의 토플 배경지식 - 화산활동


Prediction of volcanic activity

여러분 안녕하세요~

오늘은 토플의 또다른 빈출 토픽인 화산활동 예측에 대한 얘기를 해볼까 합니다.

화산을 예측하는 방법은 여러가지가 있지만, 결론적으로 말씀드리자면 현존하는 어떤 테크톨로지로도 정확하게 예측할 수는 없습니다.

토플에서 가장 자주 나오는 화산은 미국 워싱턴에 위치한 Mount St. Helens입니다. St Helens의 경우 1980년에 작은 지진이 시작되어 화산 밑의 마그마가 움직인다는 사실이 관찰되었습니다. 또한 마그마가 지하에서 위로 올라옴에 따라 북쪽지역이 융기했습니다. 그 후 몇 차례 작은 화산 폭발을 일으켰으나 전문가들은 이것이 일반적인 수직폭발이라고 예측했습니다. 그러나 예상과 다르게 1980 5 18, 갑자기 측면폭발(lateral blast)이 일어나 600㎢에 달하는 지역이 폐허로 변했으며 57명이 사망했습니다.

이렇듯 지진의 예측은 중요한 사안이 되어왔는데요, 그와 관련된 토플에 자주 나오는 개념들을 살펴보도록 하죠.


1. 지진활동도 (seismicity)

지하의 마그마가 지표로 올라오기 위해 암석을 밀면서 생기는 균열로 인한 short-period earthquake, 화산 내부의 가스 압력이 증가하면서 발생하는 long-period earthquake 그리고 지속적이고 주기적으로 발생하는 harmonic tremor로 구분

Seismic Waves (Seismicity)

[edit] General principles of volcano seismology

Seismic activity (earthquakes and tremors) always occurs as volcanoes awaken and prepare to erupt and are a very important link to eruptions. Some volcanoes normally have continuing low-level seismic activity, but an increase may signal a greater likelihood of an eruption. The types of earthquakes that occur and where they start and end are also key signs. Volcanic seismicity has three major forms: short-period earthquake, long-period earthquake, and harmonic tremor.


2. 가스 분출 (Gas emissions)

마그마가 지표면 가까이로 올라오고, 압력이 하강하면 가스가 분출되기 시작

Gas emissions

Gas and ash plume erupted from Mount Pinatubo, Philippines.
As magma nears the surface and its pressure decreases, gases escape. This process is much like what happens when you open a bottle of soda and carbon dioxide escapes. Sulphur dioxide is one of the main components of volcanic gases, and increasing amounts of it herald the arrival of increasing amounts of magma near the surface. For example, on May 13, 1991, an increasing amount of sulphur dioxide was released from Mount Pinatubo in the Philippines. On May 28, just two weeks later, sulphur dioxide emissions had increased to 5,000 tonnes, ten times the earlier amount. Mount Pinatubo later erupted on June 12, 1991. On several occasions, such as before the Mount Pinatubo eruption and the 1993 Galeras, Colombia eruption, sulphur dioxide emissions have dropped to low levels prior to eruptions. Most scientists believe that this drop in gas levels is caused by the sealing of gas passages by hardened magma. Such an event leads to increased pressure in the volcano's plumbing system and an increased chance of an explosive eruption.


3. 지형 변형 (Ground deformation)

마그마가 지표면에 가까이 올라오면서 화산지대가 융기하게 된다. 이 경사면 기울기를 관찰하여 마그마의 움직임을 예측

Ground deformation

Swelling of the volcano signals that magma has accumulated near the surface. Scientists monitoring an active volcano will often measure the tilt of the slope and track changes in the rate of swelling. An increased rate of swelling, especially if accompanied by an increase in sulphur dioxide emissions and harmonic tremors is a high probability sign of an impending event. The deformation of Mount St. Helens prior to the May 18, 1980 eruption was a classic example of deformation, as the north side of the volcano was bulging upwards as magma was building up underneath. Most cases of ground deformation are usually detectable only by sophisticated equipment used by scientists, but they can still predict future eruptions this way. The Hawaiian Volcanoes show significant ground deformation; there is inflation of the ground prior to an eruption and then an obvious deflation post-eruption. This is due to the shallow magma chamber of the Hawaiian Volcanoes; movement of the magma is easily noticed on the ground above.


4. 온도 관찰 (Thermal monitoring)

마그마의 변화에 따라 화산 표면의 온도 방사율이 변화

Thermal monitoring

Both magma movement, changes in gas release and hydrothermal activity can lead to thermal emissivity changes at the volcano's surface. These can be measured using several techniques:
•forward looking infrared radiometry (FLIR) from hand-held devices installed on-site, at a distance, or airborne;
•Infrared band satellite imagery;
•in-situ thermometry (hot springs, fumaroles)
•heat flux maps
•geothermal well enthalpy changes