Geography · Rivers & mountains
Volcanoes & lakes
How the land can shape a place.
How volcanoes shape the land
A volcano is a mountain that can explode with hot melted rock. This melted rock is called lava when it comes out. When lava cools down, it turns into hard black rock. Over many years, volcanoes grow taller as more lava piles up. Some volcano mountains are very wide and gentle like a hill. Others are steep and pointy like a cone. The shape depends on the lava. Runny lava spreads far and makes flat volcanoes. Thick lava piles up and makes steep volcanoes. Countries like Iceland and Japan have lots of volcanoes.
How volcanoes can create lakes
Sometimes a volcano explodes so hard that the top falls in. This leaves a big bowl shape called a crater. Rain fills the crater over time and becomes a lake. Crater Lake in America is a famous example of this. Some volcanic lakes are very round and deep. The water can be bright blue or green. Volcanic rock around the lake is usually dark grey or black. These lakes are special because the land beneath is still hot.
Mountains and valleys shape where rivers flow
Rivers cannot flow uphill, so mountains guide where they go. Water always travels downhill to the lowest place it can find. Mountains act like walls that rivers must flow around. Valleys are low spaces between mountains where rivers often run. Deep valleys were carved by rivers over millions of years. The river cuts into rock like a knife cutting through butter. Some valleys are narrow and steep. Others are wide and flat. The shape tells us about the river that made it.
How lakes form in different ways
Not all lakes are made by volcanoes. Some form when rivers get blocked by fallen rocks or landslides. Glaciers are huge rivers of ice that carve bowl shapes in mountains. When the ice melts, these bowls fill with water and become lakes. Some lakes form in flat land where rainwater collects in dips. The Great Lakes in North America were made by ancient glaciers. Each type of lake has a different shape and depth. The land around decides what the lake looks like.
Worked examples
1. A new volcano has runny lava that spreads far. What shape will it be?
- Runny lava flows a long way before it cools down.
- It spreads out wide instead of piling up high.
- This makes a flat, gentle volcano shaped like a shield.
2. Why do most rivers flow through valleys instead of over mountain tops?
- Water always flows downhill because of gravity.
- Valleys are the low spaces between mountains.
- Rivers follow the easiest downhill path through valleys.
3. A volcano's top collapses and leaves a deep hole. What might happen next?
- The hole is called a crater and it is shaped like a bowl.
- Rain and melted snow collect in the crater over time.
- Eventually the crater fills with water and becomes a crater lake.
Try it yourself
You see a round, deep lake surrounded by dark volcanic rock. How was it likely formed?
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