There are two main types of melanoma: radial and nodular. The radial type will grow near the skin surface and can be easy to see. They will often be raised, bumpy and irregular in shape with a mix of colours. This upwards growth is usually quite obvious.
A nodular melanoma will begin its growth stage beneath the skin with downward growth coming first. That means it can be more difficult to see changes in the mole during the early stages.
Example image of nodular melanoma: