High spring tides occur at new moon and full moon because the

High spring tides occur when the Sun, Earth, and Moon are aligned in a straight line, a configuration known as syzygy [1][t1][t5]. This alignment happens twice a month during the new moon and full moon phases [c1][t3]. During these periods, the gravitational forces of the Sun and the Moon act along a common line, reinforcing each other to exert a combined pull on the Earth's oceans [t4][t5][t8]. This results in the maximum tidal range, characterized by higher-than-normal high tides and lower-than-normal low tides [t3][t6]. In contrast, neap tides occur when the Sun and Moon are at right angles to each other relative to the Earth, causing their gravitational forces to partially counteract one another and resulting in a smaller tidal range [c2][t2].

Sources

1. [1] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 13: Movements of Ocean Water > Tides based on the Sun, Moon and the Earth Positions > p. 110