Which of the following is not an intrusive volcanic landform ?

Question

Accepted Answer

Option 3, Caldera, is the correct answer because it is not an intrusive volcanic landform. To understand why this is the case, let's explore the nature of volcanic landforms and the distinctions between intrusive and extrusive types.

1. **Explanation for Option 3 (Caldera):**
   - A caldera is a large, basin-like depression that forms when a volcano erupts and collapses. This process is extrusive, meaning it occurs on the Earth's surface. Calderas are typically formed after the magma chamber beneath a volcano is emptied during an eruption, causing the ground above to collapse. Therefore, calderas are not formed by the intrusion of magma into existing rock layers, which is characteristic of intrusive landforms.

2. **Explanation for why other options are incorrect:**

- **Option 1 (Batholith):**
     - A batholith is a large mass of intrusive igneous rock that forms from cooled magma deep in the Earth's crust. Batholiths are created when magma intrudes into surrounding rock and solidifies before reaching the surface. They are typically exposed at the surface only after extensive erosion removes the overlying material. Thus, batholiths are classic examples of intrusive volcanic landforms.

- **Option 2 (Lacolith):**
     - A laccolith is another type of intrusive volcanic landform. It forms when magma intrudes between layers of sedimentary rock, creating a dome-like structure. The pressure from the magma causes the overlying rock layers to bulge upwards. Laccoliths are formed beneath the Earth's surface, making them intrusive.

- **Option 4 (Phacolith):**
     - A phacolith is an intrusive igneous rock formation that occurs in the crests and troughs of folded sedimentary layers. Like batholiths and laccoliths, phacoliths are formed by the intrusion of magma into existing rock formations. They are typically found in association with anticlines and synclines, which are types of folds in the Earth's crust.

In summary, the correct answer is Option 3, Caldera, because it is an extrusive volcanic landform, unlike the other options, which are all intrusive.