Explanation

(a) Landforms associated with extrusive volcanic action:

- Lava plain
- Lava plateau
- Acid lava cone
- Basic lava cone/shield volcano.
- Basaltic plateau
- Parasitic cones
- Lava tongues ( in lava dammed lakes)
- Crater
- Conposite cones ( strata volcanoes)
- Volcanic plug
- Ash and cinder cone
- Pillow lava.

(b) Characteristics and mode of formation of laccoliths:

(i) Characteristics:

1. Found in areas of volcanic activity
2. Mushroom-shaped
3. It extends for several kilometers
4. it is often less than l6 km in diameters
5. An igneous rock
6. Usually has a flat base and a round top
7. Fed by pipe-like conduit from below
8. Forms base of many great mountains
9. Lies concordant or horizontal to the bedding plane
10. lt forms a mountain when exposed
11. It is resistant to erosion
12. Arches the overlying rock stratum
13. Examples are El-Koubra Djauf in Algeria, Black hills of south Dakota, Fonjay Massif in Madagascar, and Henry mountains of south Utah in USA 

(ii) Mode of Formation:

1. Formed in areas of volcanicity
2. Formed when pressure on molten magma under the earth is released into the crust
3. Thick (viscous) magma is released from the interior of the earth.
4. Magma freed through earth's movement
5. If line of weakness is obstructed by a thick layer of rock strata, upward movement stops.
6. Rising magma may come across a hard layer on its way.
7. As it cannot penetrate it, it forces the overlying layer of rock to arch upwards.
8. Causing the layer to form a great oval or semi-circular shape.
9. Magma then squeezes beneath the pushed-up/semi-circular-shaped rock.
10. This cools and solidifies to form a dome-line feature resembling a mushroom.
11. Denudation may expose it to form an upland. 

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