Shorelines geology

Summary

This video explores the dynamic nature of Southern California beaches, focusing on how sand moves throughout the year. It explains the seasonal changes where wide sandy beaches in summer give way to rocky shores in winter, driven by the size of the waves. The script delves into the processes of longshore drift and longshore currents, showing how sand moves along the coast and eventually gets carried away into submarine canyons. Viewers will gain an understanding of coastal erosion, sandbar formations, and the overall coastal ecosystem, all explained in an engaging and visually informative manner.

Takeaways

• 😀 Beaches in Southern California experience seasonal changes, with wide sandy beaches in summer and narrower, rockier beaches in winter.
• 😀 The key issue in winter is not the appearance of rocks, but the displacement of sand, which moves offshore into sandbars.
• 😀 In summer, small waves push sand toward the beach, creating wide sandy shorelines, while large waves in winter sweep the sand offshore.
• 😀 Coastal erosion and cliff failures are more common in the winter, as bigger waves reduce the width of beaches and expose cliffs to damage.
• 😀 Longshore drift (or transport) refers to the movement of sand along the beach in a zigzag pattern, driven by waves hitting the shore at an angle.
• 😀 The longshore current created by angled waves moves sand along the coast, not just on the beach but also within the surf zone before reaching shore.
• 😀 On both the East and West Coasts of the U.S., the net movement of sand is to the south, as most large waves come from the north (North Pacific or North Atlantic).
• 😀 In Southern California, sand moves southward due to longshore drift, but eventually it is funneled into submarine canyons.
• 😀 Submarine canyons like La Jolla Canyon drain sand into deeper waters, effectively removing it from the beach system and making it difficult to recover.
• 😀 The process of sand loss to submarine canyons contributes to coastal erosion, and once sand leaves the beach system, it is lost to the ocean floor.

Q & A

What causes the seasonal changes in Southern California beaches between summer and winter?

The seasonal changes are caused by the difference in wave size. In summer, smaller waves push sand toward the beach, creating wide sandy shores. In winter, larger waves push sand offshore, leading to narrower, rockier beaches.

Why does sand move offshore in the winter, and what happens to it?

In the winter, large waves break hard on the beach, sweeping the sand offshore into longshore bars or submarine canyons. This movement results in a loss of sand from the beach, which cannot easily be returned.

What is 'longshore drift,' and how does it affect sand movement?

Longshore drift, or longshore transport, is the movement of sand along the beach due to waves hitting the shore at an angle. This causes the sand to move in a zigzag pattern along the coastline, generally in the direction of the wave's travel.

What causes sand to move south along both the East and West Coasts of the U.S.?

Most of the waves that impact both coasts come from the north—North Pacific for the West Coast and North Atlantic for the East Coast. As the waves approach at an angle, they push the sand from north to south along the coastline.

How does 'longshore drift' impact the sand on Southern California beaches?

Longshore drift causes the sand on Southern California beaches to move south, where it eventually drains into submarine canyons, such as Redondo, Newport, and La Jolla canyons, thus leaving the beach system.

What is a 'beach compartment'?

A 'beach compartment' refers to an area where sand arrives at the beach, moves along it, and eventually leaves the beach through a submarine canyon, often to the ocean floor.

How do submarine canyons like La Jolla Canyon affect sand movement in Southern California?

Submarine canyons like La Jolla Canyon drain sand that moves along the beach, leading to the loss of sand from the beach system. Once sand reaches the canyon, it cannot easily be returned to the beach.

What role does wave size play in beach erosion during the winter?

During winter, larger waves contribute to beach erosion by breaking hard on the shore and sweeping sand offshore. This results in narrower beaches and exacerbates coastal erosion and cliff failures.

Why is it difficult to restore sand once it drains into a submarine canyon?

Once sand reaches a submarine canyon and drains onto the ocean floor, it is very challenging to return it to the beach system due to the depth and location of the canyon.

What personal experience does the speaker share about La Jolla Canyon?

The speaker, a scuba diver, shares that they have swum out to La Jolla Canyon, where they observed sand draining away from the beach into the canyon, noting that the sand once belonged to the beach and is now lost to the system.