START WITH A QUESTION
Will the path you used on the way out still be there on the way back?
LOOK CLOSELYFind the same rock in the low- and high-water views. The rock stays put, but the water covers different parts of it.
One coast, different water levels
Low tide
The low-water turning point.
High tide
The high-water turning point.
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High and low tide are turning points
NOTICE THISIs low tide the same as a tide that is still falling?
WHAT THIS TELLS USLow tide is the low-water turning point. An ebbing tide is still falling.
A rising tide has not yet reached high tide.
Tides are the periodic rise and fall of sea level. High tide is the turning point from rising to falling; low tide is the turning point from falling to rising.
Move the water level in the diagram. The coastline stays the same, but the area covered by water changes. High and low tide describe water levels. They do not tell you whether you can walk or swim somewhere.
Go deeper: twice a day, at the same time?
Many coasts have roughly two high and two low tides a day. The pattern varies by location and date, and two high tides need not have the same height. Times shift as the Moon moves around Earth. Do not plan by adding a fixed number of minutes to yesterday’s tide time: check a tide table for the day and place of your visit.
Think it through: the same height can lead to different changes
The same water level can occur on a rising tide or a falling tide. The next change will be different. Follow the sequence over time instead of looking at just one height.
Sources for this explanation: G1
The Moon’s pull is not equal everywhere
NOTICE THISDoes the Moon pull equally on the near and far sides of Earth?
1. The Moon pulls on the whole Earth
All parts are pulled towards the Moon, but the nearer side is pulled more strongly.
2. Compare the pull with Earth’s centre
The far side is not repelled by the Moon. It is pulled less strongly than the centre.
WHAT THIS TELLS USDifferences in the Moon's pull create a stretching effect across Earth.
The whole Earth is pulled towards the Moon. Differences in that pull help cause tides.
The side closer to the Moon is pulled more strongly than Earth’s centre. The far side is also pulled towards the Moon, but less strongly than the centre. Relative to the centre, these differences act to stretch Earth along the Earth–Moon line.
This difference is the tide-generating effect of gravity. The Sun has a similar effect. Pictures of two bulges on opposite sides of Earth simplify this principle.
Go deeper: is high tide when the Moon is overhead?
Real oceans have continents, uneven seabeds, different depths and differently shaped bays. Their response takes time and varies from place to place, so the Moon’s position alone cannot tell you a coast’s high-tide time. The model’s two bulges do not simply sweep around the real Earth unchanged.
Sources for this explanation: G1
Spring and neap tides describe the range
NOTICE THISWhat are we comparing in spring and neap tides?
Spring tide: larger range
New Moon alignment. Around full Moon, the lunar and solar effects also reinforce each other along the same line.
Neap tide: smaller range
Around the first and last quarters, the combined effects produce a smaller tidal range.
WHAT THIS TELLS USWe are comparing the difference between high and low water.
Spring tides have a larger tidal range; neap tides have a smaller range.
Around new and full Moon, the Moon’s and Sun’s tide-generating effects reinforce one another along the same line. The difference between high and low tide is larger: a spring tide. Around the first and last quarters, that difference is smaller: a neap tide.
High tide describes a turning point within a tidal cycle. Spring tide describes a period of larger tidal range. Spring tides still have low tides, and neap tides still have high tides.
Go deeper: can you plan from the Moon’s phase alone?
A spring tide is not limited to the exact day of a new or full Moon. The pattern spans nearby days, and actual times and heights vary locally. Neither ‘spring’ nor ‘neap’ means swimming is permitted. Check that day’s tide table, weather information and local instructions.
Sources for this explanation: G1
Read the place, date, time and height
NOTICE THISDoes a tide height of 100 cm mean the water is 100 cm deep?
Tide height and depth start from different levels
Fictional teaching data · Not a local forecast
09:00: low tide, 40 cmThe water begins to rise.
12:00: 100 cmStill rising; not yet high tide.
15:00: high tide, 160 cmThe water begins to fall.
WHAT THIS TELLS USTide height is measured from a reference level. Water depth is measured from the seabed to the surface.
Follow the changes between high and low tide, too.
Time runs along the horizontal axis. The vertical axis shows sea level measured above a reference level, or datum. A rising curve means the water level is going up; a falling curve means it is going down. Follow the curve through your whole visit, including your return.
The Japan Meteorological Agency’s tide tables show predicted astronomical tides. Air pressure, wind and other conditions can make the actual level different. A tide height of 100 cm does not mean the water at your feet is 1 m deep: the ground and seabed also have their own heights.
Go deeper: using an official tide table
Check the station, date, units and height datum. JMA times are Japan Standard Time. You cannot directly compare numbers that use different reference levels. An hourly graph uses hourly values; consult the high- and low-tide table as well for the predicted turning-point times and heights.
Try the numbers: one surface, different depths
In this teaching example, the reference is 0 cm and the surface is 100 cm. At A, the bottom is 40 cm above the reference, so depth is 100 − 40 = 60 cm. At B it is 60 cm below the reference, so depth is 160 cm. These invented numbers explain the terms; they are not depths or access advice for a real coast.
Sources for this explanation: G2
Your route back may disappear first
NOTICE THISCan a path disappear before high tide?
1. Lower water
Low ground is visible above water.
2. Rising water
More of the ground goes underwater.
3. The path is covered
The rocks are dry, but the path to land is gone.
WHAT THIS TELLS USLow paths can be covered before the tide reaches its highest point.
Dry rocks do not guarantee a dry route back to land.
A low path can go underwater while a higher rocky outcrop remains exposed. The Japan Coast Guard describes incidents in which people crossed to rocks at low tide and could not return as the tide rose.
Before setting out, check tide changes, weather, access restrictions and local instructions. Conditions change: a tide-table number alone cannot tell you when a route is passable.
Go deeper: is watching the high-tide time enough?
A low route may be covered before high tide. Waves can reach beyond the still-water edge, and wind or low pressure can raise water levels. Low tide is no guarantee of safety. These diagrams cannot give you safe crossing times for a real coast.
Sources for this explanation: G3
CONNECT THE PICTURE AND THE WORD
Words to remember
- Tide height
- The height of the sea surface above a specified reference level.
- Tidal range
- The difference in height between high and low tide.
- Water depth
- The vertical distance from the surface to the bottom.
CAN YOU EXPLAIN IT IN YOUR OWN WORDS?
Check your understanding
Think first, then open each question to read the explanation. You can look back at the diagrams.
Q1If the height is the same, will a rising and falling tide behave the same next?
Explanation: No. One is rising and the other is falling. Read the time and direction of change together.
Q2Does a neap tide mean it is safe to visit the shore?
Explanation: No. It means the tidal range is relatively small. Waves, wind, local terrain and instructions still matter.
LET’S THINK
A question to explore further
In our fictional chart, low tide is at 09:00 and high tide at 15:00. Can you assume a path to the rocks is passable at 12:00 because high tide has not arrived?
Show a hint and explanation
No. At 12:00 the water is already rising. A low path may be covered before high tide. The graph is also fictional. Real decisions need information about the local terrain, that day’s tide and weather, and instructions at the site.
Explore together, at home or in class
Start with the coastal comparison, then compare 09:00, 12:00 and 15:00 on the chart. Separate what the diagrams show from what requires real local information.
Sources & further reading
We developed our own explanations, diagrams and learning questions using these sources. Inclusion does not imply review or endorsement by the source organisation. Links marked “Japanese” lead to Japanese-language material.
Sources for the added diagrams and explanations
Additional sources checked: 2026-09-21. Numerical diagrams use invented teaching values.
- [G1] JMA: how tides work (Japanese) ↗High and low tides, the Moon and Sun, spring and neap tides.
- [G2] JMA: reading tide tables (Japanese) ↗Tide-height reference levels and predictions. Depth calculations use invented teaching values.
- [G3] Japan Coast Guard: precautions at the beach (Japanese) ↗Changing access as the tide rises.
Original lesson sources
- [1] JMA: how tides work (Japanese) ↗Tidal cycles, the Moon and Sun, spring and neap tides.
- [2] JMA: tide-table guide (Japanese) ↗Predictions, datums, time, hourly graphs and high/low tide tables.
- [3] JMA: tidal terminology (Japanese) ↗Tide height, tidal forces and unequal daily tides.
- [4] NOAA: What Causes Tides? ↗Differences in the Moon’s gravitational pull and the limits of simplified models.
- [5] NOAA: Is high tide when the Moon is overhead? ↗How geography and ocean depth affect local tides.
- [6] JMA: tide tables (Japanese) ↗Official predictions selected by location and date.
- [7] Japan Coast Guard: precautions at sea (Japanese) ↗People cut off by a rising tide and checks before a visit.
- [8] JMA: storm surges (Japanese) ↗Water-level changes caused by pressure and wind; why low tide is no guarantee of safety.
First published: 2026-09-20 · Updated: 2026-09-21 · Original sources checked: 2026-09-20 · Editorial policy