How the Boston Harbor Islands formed and How they are changing today By:Nicolas Santiago

Glaciers  Millions of years ago, a glacier covered our continent. It retreated and recovered the continent several times.

Melting  As the glacier melted, it left rock and dirt debris called till. As till built up, it created many different landforms.

Drumlins  One landform that glaciers created are called drumlins. A drumlin is a pile of till shaped in the direction that the glacier traveled in. When the glacier melts, water covers the land surrounding the drumlin, creating one of only two drowned drumlin fields in the world.

Erratics  As glaciers move, they pick up large boulders. When the glacier melts the rocks are dropped in random places.

Erosion by waves  As days go by, the drumlins are eroded by waves. Because of the way the glacier traveled, one side of the island gets hit harder than the other.

Impact  One way the island is eroded by waves is from impact. The force of the waves hitting the shore break apart rocks. On one side of the island, the shore is in good condition. However on the other side, the rock is broken and scatered due to the fact that one side of the island is facing the open sea.

Abrasion  Another way the waves erode the island is by abrasion. Rock and sand and other debris are in waves. When waves hit the shore, they wear down and scrath rock making them smooth, much like the effect sandpaper has.

Deposition  Waves pick up debris as they travel. When the waves lose speed, they drop it, making several different types of landforms.

Beaches  One result of deposition is a beach. Beaches in Massachusetts are made from eroded rock. Most Boston harbor islands have a beach

Longshore Drift and Spits  When waves travel at an angle, they deposit sand at an angle as well. These can form landforms such as a spit. A spit is a “finger” of sand that sticks out into the water.

Wind Erosion  There are many ways wind can cause erosion. Wind by itself is very week eroding. When it blows and there is little vegetation, it picks up loose sand and dirt, or loess, either depositing it in a different location, making large piles of loess, also known as a sand dune. Also when there is loess in the wind, it can scrape a rock smooth, a form of abrasion. Because the Boston harbor islands are exposed in the open, they are eroded by wind everyday

Erosion by Water  Water is also a major factor in erosion. When it rains, the water can cause many types of things. One result of water erosion are rills and gullies. When rain hits a hill with little vegetation, it flows downhill, forming things called rills. Rills are little grooves in the soil were the water flowed down. When rills connect, they form gullies. Gullies are larger rills were water flows down. When water flows down, the sediment gets caught in the water. This is called runoff.