earth science

Sunda Arc

Sunda Arc is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Sunda Arc rather than just read about it. In short: The Sunda Arc is a volcanic arc forming the topographic spine of the islands of Sumatra, Nusa Tenggara, Java, the Sunda Strait, and the Lesser Sunda Islands. The Sunda Arc begins at Sumatra and ends at Flores, and is adjacent to the Banda Arc.

Key takeaways

Sunda Arc belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Sunda Arc to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sunda Arc from memory before moving on to harder problems.

Reference excerpt

The Sunda Arc is a volcanic arc forming the topographic spine of the islands of Sumatra, Nusa Tenggara, Java, the Sunda Strait, and the Lesser Sunda Islands. The Sunda Arc begins at Sumatra and ends at Flores, and is adjacent to the Banda Arc. The Sunda Arc is formed via the subduction of the Indo-Australian Plate beneath the Sunda and Burma plates at a velocity of 63–70 mm/year.

Formation and geologic setting Mid-oceanic ridge basalts (MORB) form most of the oceanic basin south of Sunda, according to geodynamic studies. These plates began to converge in the Early Miocene. The Indo-Australian Plate is subducting beneath the Eurasian Plate with a dip angle of 49–56 degrees. The slab subducting under Java is continuous down to the lower mantle. However, the slab appears to beak apart under Sumatra Island. Earthquake depth records indicate that there is no deep seismic activity in Sumatra, likely due to the age of the subducting complex. Two types of subductions have been identified along the Sunda Arc: 1) orthogonal subduction along Java and 2) oblique subduction on the Sumatra side. These subductions are separated by the Sunda Strait.

Notable seismic events With the ongoing magmatic activities and the nature of the subduction zone, Sunda Arc has experienced major seismic events throughout history. These events cost the loss of lives and vast destruction along the coast. These are some major seismic events that have been recorded.

Tsunami in December 2004, Indian Ocean In 2004, a tsunami in the Indian Ocean was triggered by an earthquake of 9.15 magnitude near Sumatra Island. In the Banda Aceh area, the tsunami height reached up to 35 meters, which surpassed the value recorded before this event.

Tsunami in July 2006, West Java and Central Java, Indonesia An earthquake and tsunami occurred on July 17, 2006, causing major destruction in West Java and Central Java. The Mw-7.7 earthquake-induced tsunami struck over 250 km of the coastline and caused more than 600 deaths. The approximate run-up height was about 4–6 meters.

Historic eruptions and arc volcanism The Sunda Arc is home to some of the world's most dangerous and explosive volcanoes. The 1815 eruption of Mount Tambora on Sumbawa and the 1257 eruption of Mount Samalas on Lombok were among the largest in the last two millennia, ranking 7 on the VEI scale. The Sunda Arc subduction zone was also the site of one of the largest known eruptions of the Cenozoic, the VEI 8 Toba supereruption on Sumatra, which expelled 2,800 km3 of magma c. 74,000 BP. The resulting caldera has become Lake Toba. The loudest noise in recorded history occurred during the 1883 eruption of Krakatoa and was heard 5,000 km (3,100 mi) away. Hundreds of thousands of people have been killed by these eruptions and by episodes of activity at other volcanoes, including Papandayan, Galunggung, Merapi, Kelud, Sinabung, and Agung.

Main-arc volcanism

The main-arc volcanism along Sunda is mainly derived from the interaction between the Indo-Australian Plate and the Eurasia Plate. Magma originates from the partial melting of the mantle wedge driven by the fluids from the subducting slab. In addition, volcanic rocks from the Quaternary generally show more enrichment in alkaline contents than those from the Tertiary age. The majority of basalts of the arc have calc-alkaline contents, except for some potassic lava production in East Java.

Back-arc volcanism The magmatic activities along the back-arc may or may not relate to the main arc materials. Magma and lava appear to have originated from molten materials at a deeper part of the mantle as supported by a higher K2O/Na2O ratio in comparison to other parts of Sunda Arc. The most salient volcanoes in the back-arc region are Lasem, Muria, and Bawean in which their volcanic rocks show complex patterns in terms of chemical signature.

Major islands

Java Java Island is located on the east side of the Sunda Arc, located between Sumatra and Bali. Its oceanic crust's thickness is approximately 20–25 kilometers. With the geological activities and the tectonic nature of Sunda Arc, megathrust earthquakes and volcanic activities are ubiquitous on Java island. Modern volcanoes at Java are formed during the Tertiary with typical products of andesitic composition and progressively get more alkali content during the Quaternary. Along the Java island, there are approximately 62 geothermal fields that can be utilized for further usages including producing electricity. Java is also a germinal center for supplying gold and copper in which the occurrences of these low-sulfidation (LS) epithermal deposits may associate with magmatic arc activities with the spatial relationship between the akaditic magma and porphyry Cu-Au deposits.

East Java Most volcanic activity in East Java is Plinian-type, which is very explosive and emits columns of hot volcanic debris. The adiakitic magma, which deviates from usual island-arc magma, is associated with porphyry deposits. There is evidence that the Ringgit-Beser volcanic complex also produces potassic and magnesian lava, which could be a result of the decreasing influence of subduction-related material. A major volcano in East Java is Mount Bromo.

Central Java There exist two main arcs at Central Java which are Southern Mountain Arc (SMA) and Modern Volcanic Arc (MVA) which give rise to frequent volcanic activities. Prior studies suggested that SMA was formed during the Middle Eocene, followed by the subduction that resulted in the formation of MVA in the Late Eocene. Central Java is home to one of the most notorious volcanoes, Merapi, as well as other major volcanoes such as Merbabu, Muria, and Slamet. Mount Merapi is the most active volcano in Indonesia which erupts periodically every 2–6 years and has shown perennial volcanic activities dating back roughly 2000 years ago based on carbon isotopic signatures. The earliest eruption has been approximated to be roughly 40,000 years ago. The most recent significant eruptions occurred in 1994, 2006, and 2010. Mount Merapi is a steep stratovolcano situated on Central Java Island with seismic and volcanic activities that could pose major threats to countless lives and infrastructures in its vicinity. Most recent volcanic activities are induced by the collapse of the lava dome, contributing to the highly explosive eruption of andesitic materials.

… excerpt ends here. Continue reading the full article.

Illustrations

Sunda Arc: A map showing chains of volcanoes in Indonesia — A map showing chains of volcanoes in Indonesia

Worked examples

Example 1 — a first encounter with Sunda Arc

Start with the simplest possible case. Write down what Sunda Arc claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sunda Arc before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sunda Arc ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sunda Arc

In research: Sunda Arc appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sunda Arc in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sunda Arc is common in secondary-school and first-year university syllabi. It links to neighbouring topics Arcs of Indonesia, Geology of Indonesia, Greater Sunda Islands, so understanding it makes those chapters shorter.
In everyday life: Look for Sunda Arc outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Sunda Arc in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sunda Arc means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Sunda Arc out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sunda Arc in simple terms?

Why does Sunda Arc matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sunda Arc?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sunda Arc.